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Archive for the ‘Advanced Persistent Threats’ Category

Shell Team Six:Zero Day After-Party (Part VI)

Monday, April 27th, 2015

This is the final part of a six-part blog based on the paper submitted by my colleague Gregory and myself on Advanced Persistent Threats (APT), for AVAR 2014. Continuing from the fifth part of our paper…

Data Exfiltration and Cleanup



This stage of the APT involves the assailants collecting the sensitive data and transmitting it stealthily to a remote location. Data extraction can either be a one-time event or spread over a period of time, followed by constant snooping of the victim, all the while remaining hidden.

Once the objective of an APT campaign is achieved, the attackers exit the network in a phased manner after covering their tracks and clearing all the potential evidence of an intrusion.  The attackers could also plant or manipulate data in the target’s environment in an effort to create misdirection.

Extraction methodology

Confidential data that is collected during the period of the APT is copied to a staging server, compressed, encrypted and kept ready for transfer. Outbound sessions are then established that resemble legitimate traffic thereby attempting to fly under the security radar. The confidential data is thus extracted possibly in small chunks over a period of time.

The bad actors could exfiltrate data using any/all of the following methods:

HTTP/FTP/Cloud Storage Uploads

An HTTP/FTP upload or a cloud transfer is initiated by an application which is already approved by the firewall. Additionally, the packets could be SSL or custom encrypted making it difficult for security solutions to sniff.

Outgoing Emails with Password Protected Attachments

Sensitive contents are password protected and then transmitted using either a compromised employee’s email credentials, or by using a custom SMTP server.

Customized DNS Queries

Small chunks of data such as user credentials may be sent as custom DNS requests to DNS servers controlled by the attackers. The packets are then reassembled as required at the attackers end.

Fig.14. shows encrypted data sent as a DNS query

VPN/IPv6 Tunnels

VPN and IPv6 tunnels are created from the staging server to a remotely controlled machine. The contents are then securely transmitted through these tunnels.


The hacking outfit commonly known in computer security circles as Comment Crew [13] has been observed using the above data exfiltration techniques. Sensitive data which could potentially be Gigabytes in size would first be collected in a centralized location & compressed in a password-protected RAR file. The final archives would be split into chunks and uploaded using FTP, custom file transfer tools, etc.

Cleanup Methodology

The attackers tend to delete their malicious code and its associated components by remotely issuing self-destruct commands from their C2C server. A time/event bound kill switch built into the malicious code could also be automatically triggered to avoid being caught.

System logs that maintain login attempts, security logs that maintain protection status, audit files that track system changes, etc. are modified by the attackers to make a forensic reconstruction of the attack impossible.

Indicators of Compromise

Capturing and transmitting confidential data is the raison d’etre of any APT. In order to facilitate this transmission, the attacker must contact external servers from inside the victim’s network.

Here are some of the common symptoms that indicate suspicious activity within the organization’s network:

Wrong Data in the Wrong Place

Movement of encrypted or confidential data from a machine containing sensitive information to a potential upload server with Internet access, all within the organizations internal network could indicate that something is wrong.

Similarly, availability of large quantities of known-encrypted or sensitive data on a machine it’s not supposed be on could also indicate that something is amiss.

Anomalous Traffic


The following anomalies could indicate a compromise:

  1. Connections made directly to IP addresses
  2. HTTP/FTP connections on non-standard ports
  3. Connections to previously unused or high risk geo locations
  4. Accessing algorithmically generated domain names (DGA)

Other Indicators

Inconsistent events in audit logs maintained at network and endpoint level, changes in the system drivers list without an application uninstallation progress, etc. can also be used as indicators of compromise.

Prevention/Detection

Confidential information is the crown jewel of any company and typically it is this information that the attacker is focused on stealing. The following solutions can be involved in protecting the exfiltration of this confidential data:

Hardened DNS Servers


Outgoing DNS queries should be logged and monitored extensively for anomalies. Organizations could also create and maintain their own hardened DNS servers.

Security Solutions

Data aware technologies like Data Leakage Prevention (DLP) can be added to the organization’s existing layer of defense. Once critical and confidential data is identified, DLP solutions track and prevent this data from falling into the wrong hands.

URL scanners with built-in reputation intelligence can be used to detect:

  1. Access to subdomain/domains which are not popular or appear suspicious
  2. Repeated attempts to connect to domains which no longer resolve
  3. Attempts to connect to blacklisted or malicious IP addresses/domains
  4. Newly registered domains

Network scanners with Deep Packet Inspection and machine learning capabilities can be used to build a knowledge base of general network usage trends. Alarms are raised when deviations exceed pre-defined thresholds. This knowledge base includes:

  1. Commonly used protocols with source and destination information
  2. Common geo locations contacted
  3. Number of connections and the length of connections made depending on the time of the day

Software that take disk backups and dump physical memory images at regular intervals are of great help during incident response and forensic analysis of a potential APT attack.

Conclusion

The implications of the complexity and perseverance of Advanced Persistent Threats are of major significance to the existing security infrastructure. The evasion techniques discussed in this paper have exerted colossal pressure on the current methods used to detect and report these threats, especially where the human element is involved.

Safeguarding oneself against APTs requires more than just traditional security solutions. The need of the hour is a comprehensive, holistic security plan that intelligently integrates events reported from numerous forms of security established at various levels of the organization. This solution should be able to handle massive volumes of logs and spot patterns of an attack, find sources of a breach and stop new threats in their tracks.

Things are about to get a whole lot more difficult with compromised mobile devices joining the fray. Strategies to identify and stop sophisticated, multi-pronged APT attacks have been discussed; however coordinated implementation is far from straightforward. We live in interesting times.

References:

[13] http://intelreport.mandiant.com/Mandiant_APT1_Report.pdf

Lokesh Kumar
K7 Threat Control Lab

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Shell Team Six:Zero Day After-Party (Part V)

Friday, April 10th, 2015

This is the fifth part of a six-part blog based on the paper submitted by my colleague Gregory and myself on Advanced Persistent Threats (APT), for AVAR 2014.

Continuing from the fourth part of our paper

Expanding Access and Strengthening Foothold

The device that falls first is usually not the primary target of the APT. This backdoored computer is instead used as a base to search and compromise more devices that likely contain credentials to other workstations, application servers, etc. The assailants move laterally within the network, gaining access to these machines, strengthening their foothold, all the while hunting for valuable target information which was the objective of the attack.

Expansion Methodology

The initial infected host connects back to a command and control (C2C) infrastructure controlled by the bad actors. It sends critical information such as password details, privileges of the currently logged user, mapped drive information, etc. and awaits further instructions. The following techniques are used by the attackers to expand their access:

Privilege Escalation

The attackers exploit privilege escalation vulnerabilities to escape the confines of a limited user’s account. The objective here is to gain “root” on the infected machine which enables them to perform tasks that require elevated privileges such as creating/deleting system services, accessing critical process’ memory space, mapping internal networks, etc.

Fig.13: Privilege escalation code used from the Council for Foreign Relations Watering Hole attack

Remote Exploitation

Malware components can exploit network vulnerabilities to compromise systems accessible in the local network. The Stuxnet malware exploited a 0day Print Spooler (CVE-2010-2729) remote code execution vulnerability to propagate itself into new machines.

Installing More Tools

During the initial compromise, the malware authors use custom zero-day code that exploits vulnerabilities in common applications. In the expansion stage of the APT though, to avoid having to re-write code, the bad actors tend to use standard tools.

These tools could include system utilities like PsExec [9], network packet sniffers like tcpdump [10], password extracting tools like gsecdump [11], Cain&Abel [12], etc.

Obtain Credentials

With the help of the tools installed, the attackers brute-force login credentials to workstations and servers that likely contain sensitive data.

They could establish remote desktop sessions to these machines and eventually make their way onto domain controllers that have unrestricted access to the entire network.  They then begin their hunt for the target data to be extracted, if they haven’t found it already, that is.

Indicators of Compromise

Once the assailants possess domain level credentials, their movement within the network resembles that of legitimate traffic and so becomes very difficult to track. The following behaviors on the other hand could indicate a compromise and are relatively easy to track:

Presence of Unwarranted Files

Unauthorized use of kernel modules to elevate ones privileges could imply a compromise. The presence of unapproved software, modified versions of existing drivers containing trojanized code, tools like port scanners, password crackers, network sniffers, etc. could also indicate a compromise.

Login Irregularities

Repeated failed login attempts using non-existent user accounts, successful login attempts to machines that deviate from established baseline logins, login activity at odd hours, etc. could mean something is amiss.

Anomalies in Security Settings

Unauthorized disabling of security software, tampering of exclusion lists in firewalls and Anti-Virus, even for a brief period of time, could indicate a compromise.

Anomalies in User Account Activity

Changes in behavior of a user account such as time of activity, type of information accessed, systems accessed, etc. could indicate a compromise.

Prevention/Detection

Along with multi-factor authentication for sensitive accounts, updated Anti-Virus software that detects unwanted tools, a strong password policy, etc. the following solutions can be implemented to augment the network’s security:

Unified Extensible Firmware Interface (UEFI) and Secure-Boot

Privilege escalation attempts can be significantly reduced by using UEFI/secure-boot enabled machines that provide a level of trust from boot-up time.

Early Launch Anti-Malware (ELAM)

Security solutions with early loading components that are capable of detecting and blocking unauthorized kernel code should be installed throughout the network.

Click here to read the final part of this blog

References:

[9] http://technet.microsoft.com/en-us/sysinternals/bb897553
[10] http://www.tcpdump.org
[11] http://www.truesec.com/Tools/Tool/gsecdump_v2.0b5
[12] http://www.oxid.it/cain.html

Lokesh Kumar
K7 Threat Control Lab

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Shell Team Six:Zero Day After-Party (Part IV)

Friday, March 13th, 2015

This is the fourth part of a six-part blog based on the paper submitted by my colleague Gregory and myself on Advanced Persistent Threats (APT), for AVAR 2014.

Continuing from the third part of our paper…

Security Solutions Bypass

The next layer of defense that an attacker confronts is the end point security provided by third party vendors. Host Intrusion Prevention Systems (HIPS) for example, detect ROP exploitation and prevent shell code execution by injecting their modules into commonly exploited applications and placing hooks at various operating system APIs. However, these inline hooks meant to monitor suspicious activities and detect exploitation attempts are placed under the same privilege as the rest of the code in the process, thereby undermining the security solution’s ability to maintain and intercept all the required APIs.

Hook Hopping

This technique involves the attackers executing standard function prologues of intercepted APIs within self and then transferring control just past the JMP instruction intended to intercept the call.

Fig.10: Control flow depicting bypass of JMP instruction in a hooked API

The DeputyDog campaign [6] which exploited the CVE-2013-0389 vulnerability, employed the above technique to bypass the interception of WinExec() API calls by security software.

Direct SYS Calls

These are a sequence of CPU instructions that transfer control to the kernel directly from the application code instead of using the OS provided user mode APIs.

Payload Delivery via Documents or Sparse Encrypted Fetches

Shell code used as part of the exploitation chain may need to execute a larger payload to establish a backdoor on the machine. To prevent this payload from being detected by security scanners, the attackers can:

  • Embed the payload in popular document formats like PDF, DOC, etc. The shell code when run, locates this payload in the document by scanning for specific magic markers, extracts it and executes it, or
  • Download smaller encrypted chunks of the larger payload stealthily onto the victim’s machine. These chunks are later reassembled and executed on the victim’s machine.

Anti-Virus Bypassing

The attackers use custom cryptors to encrypt their malicious code and attempt to defeat traditional signature based Anti-Virus scanners. At times, these files are digitally signed using trusted stolen certificates to appear legitimate and to circumvent local system policies.

The notorious Stuxnet malware for instance used malicious kernel drivers signed with valid stolen digital certificates to bypass Anti-Virus scanners.

Equipped with information about the security solutions installed in the organization’s end point, these payloads are often tested for detection by the vendor’s security scanner before they are deployed onto the victim’s machine.

Volatile Threats

The attackers execute their malicious payloads directly on the victim’s machine without ever writing the file on the machine’s disk. Traditional security solutions that scan only files on the disk in real-time cannot see these malicious payloads that are directly written and executed in memory. Behavioral analysis systems do not intercept these operations either fearing additional performance overheads.

In the BaneChant APT campaign [7], the shell code downloaded an innocuous XOR encoded binary as the first level payload. This binary in turn downloaded a second level payload which was an executable impersonating an image file meant to bypass security scanners. Once downloaded, this binary was executed directly in memory.

Indicators of Compromise

The initial compromise stage of an APT represents an attacker’s attempts to gain entry into the target organization’s network.  In an environment defended by multiple layers of logging and security, it becomes quite a challenge for an attacker to be successful without leaving behind digital footprints. Provided below are some symptoms that could indicate a compromise in an organization’s network:

Suspicious System Changes

The presence of unauthorized applications that start from uncommon auto-start locations could indicate a compromise. Files names that resemble popular/operating system files like svchost.exe, acrord32.exe, etc. and dwell in unusual locations should also raise suspicion levels.

Fig.11: System file name present in an unusual auto-startup location

Hidden instances of popular applications like Internet Explorer, code-injection attempts into trusted operating system related processes, installation of unauthorized software, loading of driver files without an entry in the Service Control Manager, etc. could also indicate compromise.

Unusual Disk Activity

Exploitation attempts using heap spray techniques tend to use significant amounts of memory.

At times this can lead to high disk activity due to frequent page-file access. Attempts to sweep a user’s profile area for personal or confidential data could also result in increased disk activity, which could indicate compromise.

Compromised Security Components

Partially enabled security features or completely disabled security solutions on endpoints, even for a brief period of time, could indicate that something is wrong.

Loading of Unsigned Drivers in x64 Systems

x64-based Microsoft Windows verifies and allows only digitally signed driver binaries to load during system boot-up. Unsigned malware that want to load early on during the boot process will have to disable this verification process.

Boot kits for instance, tend to bypass the driver signing policy by making persistent system wide changes. Successful loading of a custom unsigned “test” driver on a machine infected with such a boot kit could indicate a compromise.

Fig.12: Windows alerting on loading an unsigned driver

Prevention/Detection

Mock Phishes

Since human behaviour is manipulated to the attacker’s advantage during this stage of an APT, training programs should be conducted at regular intervals to educate the users on the latest intrusion techniques. These programs should aim at explaining the importance of security along with adequate examples, as well as changing user behaviour such that they follow security policies correctly.

Pen test emails mimicking a spear phishing attack could be used to improve the employees’ resilience towards such attacks [8].

Virtualization

Email applications and web browsers could be run in a virtualized environment that is automatically reverted during startup.


Malicious email attachments and drive by downloads would be contained within this environment and reboot resilient code would not survive a revert-to-clean-snapshot assuming that the malware cannot escape the guest VM and infect the host.

Intent to View

Suspicious or unknown email attachments should explicitly be stripped by security solutions.

These attachments should be released to a user only if he/she explicitly requests them.

Detecting Bypassing Attempts

Evasion techniques such as hook-hopping can be identified by breaking some basic assumptions made by the attacker. The security solution can replace the random number of instructions from the function prologue with its own code sequence. This way, shell code that attempts to bypass the initial JMP instruction would still land on the code sequence controlled by the security solution.

Few security solutions use multiple int 0×3 instructions past the initial JMP instruction to trigger a debug exception when executed, breaking the flow of execution.

Hook bypass attempts using direct system calls from user-mode processes can be flagged using a kernel module, if this user-mode to kernel-mode transition does not originate from the native layer.

Click here to read the fifth part of this blog

References:

[6] http://www.fireeye.com/blog/technical/cyber-exploits/2013/09/operation-deputydog-part-2-zero-day-exploit-analysis-cve-2013-3893.html
[7] http://www.fireeye.com/blog/technical/malware-research/2013/04/trojan-apt-banechant-in-memory-trojan-that-observes-for-multiple-mouse-clicks.html
[8] http://phishme.com/product-services/what-is-phishme

Lokesh Kumar
K7 Threat Control Lab

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Shell Team Six:Zero Day After-Party (Part III)

Monday, February 23rd, 2015

This is the third part of a six-part blog based on the paper submitted by my colleague Gregory and myself on Advanced Persistent Threats (APT), for AVAR 2014.

Continuing from the second part of our paper…

Exploiting Popular Applications

Popular applications such as web browsers, word processors, etc. in an attempt to provide rich functionality, at times fail to handle untrusted data properly. The attackers probe these applications with a variety of mechanisms such as fuzzing, reverse-engineering, study of any stolen code, etc. in order to discover bugs that allow them to execute malicious code without any user interaction.

Lack of buffer boundary checks in the application’s code is exploited, critical memory area is over written to hijack the control flow of the program and  execute the attacker’s shell code.

Likewise, bugs in handling multiple references to the same object have lead to Use-After-Free class of vulnerabilities which after seeding memory areas with malicious code can be exploited to execute the attacker’s shell code.

Data Execution Prevention (DEP) Bypass

DEP is a security feature provided by the operating system to thwart buffer overflow attacks that store and execute malicious code from a non-executable memory location. The OS leverages the No-eXecute technology in modern day CPUs to enforce hardware assisted DEP that prevents memory areas without explicit execute-privilege from executing. Attempts to transfer control to an instruction in a memory page without execute-privilege will generate an access fault, thereby rendering the attack ineffective.

Bypassing the DEP feature in a process involves locating already existing pieces of executable code from process memory space and manipulating them to use attacker controlled data to achieve arbitrary code execution. This is accomplished using one of the following techniques:

  • Return-to-libc
  • Branch Oriented Programming (BOP)
    • Return Oriented Programming (ROP)
    • Jump Oriented Programming (JOP)

Return-to-libc

This evasion technique involves replacing the return address on the call stack with that of an existing routine in a loaded binary. The parameters/arguments that are passed to such routines are controlled by the exploit data strategically placed on the stack.  A system function like WinExec() can be invoked to load and run a malicious component without running non-executable exploit data.


Fig.6: The stack layout when using return-to-libc attack to invoke system() in GNU Linux (32-bit).

Branch Oriented Programming

This bypassing method involves an attacker gaining control of the call stack and executing carefully stitched pieces of executable code called “gadgets”. These gadgets contain one or two instructions which typically end in a return instruction (ROP) or a jump instruction (JOP) and are located in a subroutine within an existing program or a shared library. Chained together, these gadgets allow an attacker to perform arbitrary operations on a machine.

Fig.7: ROP gadget execution sequence based on exploit controlled stack layout

Address Space Layout Randomization (ASLR) Bypass

In order to thwart BOP attacks, the concept of randomizing executable code locations, by randomizing the base address of the loaded binary, on every system reboot was introduced. This security measure known as ASLR made it difficult for the attacker to predict where the required gadget sequence resides in memory. However, APTs have been observed bypassing this protection using the following techniques:

Loading Non-ASLR modules

Dynamic-Link Libraries compiled without the dynamic-base option cannot take advantage of the protection offered by ASLR and as a result, are usually loaded at a fixed memory space. For example, Microsoft’s MSVCR71.DLL shipped with Java Runtime Environment 1.6 is usually loaded at a fixed address in the context of Internet Explorer making it easy to construct the required gadget chain in memory.

Fig.8: An ASLR incompatible version of MSVCR71.dll

DLL Base Address calculation via Memory Address Leakage

This technique involves determining the base address of any loaded ASLR-compatible DLL based on any leaked address of a memory variable or API within that DLL. Based on the address of this known entity, the relative addresses of all the required gadgets can be calculated and a ROP attack constructed.

Attack techniques such as modifying the BSTR length or null termination allows access to memory areas outside the original boundaries, leading to the memory address of known items being revealed to the exploit code. This can then be used to pinpoint the DLL’s location to use ROP gadgets within it. Array() object also has a length component that can be overwritten to leak memory addresses beyond its bounds.

Browser Security Bypass

Leveraging the operating system’s security, popular web browsers run certain parts of their code, JavaScript execution and HTML rendering for example, as a sandboxed background process. This process runs with limited privileges and has restricted access to the file system, network, etc.  A master controller acting as an intermediary interacts with the user and manages these sandboxed processes. By using this master-slave architecture and providing a controlled environment, users are protected from exploit attempts by limiting a shell code’s capability to access host system resources and confining its damage to within the sandbox.

Since these browsers rely on the operating system’s security model, exploiting unpatched kernel vulnerabilities will result in the malicious code escaping its confined environment. The infamous Duqu malware relied on vulnerability (CVE-2011-3402) in the Win32k.sys driver that improperly handles specially crafted True Type Font (TTF) files. This allowed the malware to escape a user-mode sandboxed environment implemented by the Microsoft Word process and compromise the host.

Fig.9: Vulnerable code snippet from win32k.sys that lead to the Duqu TTF exploit

Enhanced Mitigation Experience Toolkit (EMET) Bypass

EMET is a Microsoft tool that provides additional security to commonly-exploited third-party applications such as web browsers, word processors, etc. It extends the operating system’s protection mechanisms to these vulnerable applications and makes exploitation attempts extremely difficult.

The following table lists the protections offered by EMET and known bypassing techniques [4]:

Click here to read the fourth part of this blog

References:
[4] http://bromiumlabs.files.wordpress.com/2014/02/bypassing-emet-4-1.pdf
[5] http://0xdabbad00.com/wp-content/uploads/2013/11/emet_4_1_uncovered.pdf

Lokesh Kumar
K7 Threat Control Lab

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Shell Team Six:Zero Day After-Party (Part II)

Wednesday, February 11th, 2015

This is the second part of a six-part blog based on the paper submitted by my colleague Gregory and myself on Advanced Persistent Threats (APT), for AVAR 2014.

Continuing from the first part of our paper

Initial Compromise

Armed with information obtained from the previous stage, the perpetrators may adopt several techniques to sneak into the organization. Traditional attacks involve actively targeting vulnerable applications and exploiting Internet facing resources like webservers, SQL servers, FTP servers, etc. As log analysis and security around these external resources have caught on, the attackers have had to evolve their tactics in order to be successful.

Infiltration Methodology

The attackers now target the most vulnerable element of any organization – the human. Social engineering tactics are used to entice an individual or a group of users into running code, which will allow the attackers to introduce their malware into the organization’s network. The most commonly used attack techniques are:

  • Spear Phishing
  • Watering Hole

Spear Phishing

Spear phishing involves the attacker compromising a machine by sending a well-crafted email to a targeted user and convincing him/her to:

  • Open an embedded link that points to a website loaded with zero-day exploits, or
  • Open a malicious attachment (EXE, PDF, DOCX etc.)

both of which exploit the rendering application to drop or download, and execute a payload with backdoor capabilities

Watering Hole

 

Watering hole attack involves the attacker placing exploits, possibly zero-day in nature, on a trusted website which is frequented by the users of the organization.  When a targeted user visits the site, the exploit code is automatically invoked and the malware installed on his/her machine.

Case Study

The U.S. Veterans of Foreign Wars’ website was recently compromised to serve a zero-day exploit (CVE-2014-0322). A similar watering hole attack exploiting zero-day vulnerabilities has occurred in the past targeting a specific group of people by compromising the website of the Council for Foreign Relations.

Fig.2 shows publicly available website access logs of users along with their non-routable IP addresses. This information can be used to evaluate the browsing habits of individuals in the company and eventually to execute a watering hole attack.


 
Fig.2: Publicly available map of internal IP addresses and their website logs

Security Bypassing

Email attachments, file downloads, HTTP requests, etc. originating from users undergo rigorous checks at various layers that include:

  • Network/Gateway layer scanners
    • Email/File/URL scanners
    • Sandboxed file analysis
  • Endpoint/Desktop layer scanner
    • Anti-Virus/HIPS/firewall
    • Application security features
    • Operating system security features

Once the human element falls prey to social engineering, and is coaxed into downloading a file/email or visiting an exploit site, the attackers are faced with challenge of defeating a series of network and end point security solutions before conquering the victim’s machine. Listed below are some of the tactics used by the perpetrators to bypass these layers of security.

Attachment Archive File Format Abuse

Discrepancies in the way in which a security product handles a compressed file versus that of an un-archiving application has led to abuse of the popular ZIP file format.  Un-archiving apps identify ZIP file types by scanning the last 64KB of the file for a special magic marker. Security scanners on the other hand, with a need for speed, identify the file type by inspecting only the first few bytes from the beginning of the file.

An attacker abuses this disparity by creating a malicious ZIP file and manipulating its headers by adding junk data at the beginning of the ZIP file. This specially crafted file deceives security scanners into thinking that it is of an unknown type and escapes detection, but un-archiving applications are able to successfully extract the malicious code at the end point.

Fig.3 shows a Proof-of-Concept [2] archive file that is capable of evading security scanners

Fig.3: Crafted ZIP file with NULL data prefixed.

Gateway Sandboxing Bypass

Suspicious files that match certain criteria are typically executed within a sandboxed environment for a short period of time. Depending on their behavior, the files are either blocked from the user or released to him/her.

Attackers can craft malicious files which detect such controlled settings by looking for specific registry keys, in-memory code changes, mouse pointer movement, etc.

For example if the malicious file identifies that it is being executed in a sandboxed environment, it stays idle without performing any activity thereby bypassing this check. The Up-Clicker Trojan [3] attempts to evade sandbox analysis by staying idle and waiting for a mouse click before activating itself.

Fig.4: Code showing Up-Clicker Trojan set to activate on mouse click

Browser Multi-Purpose Internet Mail Extensions (MIME) Sniffing

This attack exploits differences in the way in which security scanners and web browsers identify the content returned by an HTTP server.

Security scanners parse the magic headers available at the beginning of a file returned by the web server, to identify the file type. This means that a specially crafted malicious HTML file containing the magic marker commonly found in a GIF image will be identified by the scanner as an image file, exempted from scanning and let through into the network.

Web browsers on the other hand, depend on the MIME type in the HTTP response header returned by the web server to identify the file type. When this information is absent as is the case of a response from an attacker controlled web server, the web browser resorts to content sniffing to determine the MIME type. So, the same malicious HTML containing the GIF magic marker will now be identified as HTML content by the user’s browser and rendered accurately to execute the exploit code.

Fig.5: Malicious script containing bogus RAR and GIF magic markers.

Click here to read the third part of this blog

References:
[2] http://www.reversinglabs.com/news/vulnerability/reversinglabs-vulnerability-advisories.html
[3] http://www.infosecurity-magazine.com/news/trojan-upclicker-ties-malware-to-the-mouse

Lokesh Kumar
K7 Threat Control Lab

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Shell Team Six:Zero Day After-Party (Part I)

Wednesday, January 21st, 2015

This is the first part of a six-part blog based on the paper submitted by my colleague Gregory and myself on Advanced Persistent Threats (APT), for AVAR 2014. This first part introduces the reader to the different phases of an APT and discusses the methodology, prevention and detection techniques of the initial phase of an attack in detail.

The IT security industry is faced with the challenge of dealing with old invasion tactics that have been reborn in new avatars as Advanced Persistent Threats (APTs). APT attacks are tenacious at pursuing their targets and are played out in stages, possibly over a long period of time. With financial backing from state actors and criminal rings, APTs tend to be compound, sophisticated and difficult to detect. Each facet of the intrusion, in an idealist scenario, may be refined to such an extent that the end goal is achieved without a trace before, during or after the event.

Despite the complexity of these types of attacks, certain parameters always need to be satisfied to deliver the payload and retrieve the expected results, leading to the emergence of an attack pattern which may be placed under the microscope and flagged. These parameters include executing arbitrary code by invoking zero-day exploits for popular software, defeating security measures such as DEP & ASLR, e.g. via heap spray and ROP/JOP chains, exploiting EoP vulnerabilities, establishing remote C&C communication channels to issue commands or to exfiltrate stolen data in encrypted form, etc.

Drawing on evidence from documented real-world case studies, this paper details techniques that assist an assailant during the different phases of an APT, bypassing protection mechanisms like application-sandboxing, EMET, IDS, etc. thus attempting to fly under the defense radar at all times. Equipped with this information, we hope to explore methods of discovering each part of the life-cycle of a targeted attack as it is in progress or in the post mortem, thus reducing their efficacy and impact.

Introduction

“If you know your enemies and know yourself, you will not be imperiled in a hundred battles… if you do not know your enemies nor yourself, you will be imperiled in every single battle.” Sun Tzu

As technologies implemented in organizations are becoming advanced, the threats are rapidly evolving too. Through tenacious and coordinated attacks on one’s infrastructure, APTs are able to infiltrate and overwhelm the organization.

The threat landscape has changed. But the general principles of war remain the same.  Knowing the modus-operandi of your faceless attackers helps one evaluate, and harden one’s security measures, and gear up towards facing the attackers head on.  This paper aims to help you do just that.

APT Life-Cycle

The stages of an APT can broadly be classified as follows:

•   Target reconnaissance
•   Initial compromise
•   Expanding access and strengthening foothold
•   Data exfiltration and cleanup

 

 Target Reconnaissance

The reconnaissance phase of a targeted attack sets the stage for the rest of the threat campaign and therefore involves a high degree of planning. The perpetrators spend significant amounts of time learning about their target, collecting as much information as possible about the human, physical and virtual resources of the organization. The intelligence garnered during this stage not only helps the assailants determine key points of entry into the target network but also empowers them to navigate the victim’s network once inside more effectively & efficiently.

Reconnaissance Methodology

The target’s virtual network is plotted using publicly available resources. These resources include:

•   DNS records
•   WHOIS information
•   Email messages
•   Inadequately protected network logs
•   Misconfigured servers, etc.

The organizational structure is also studied to determine employees and their organizational access levels, using social media, search engines and the target’s own website. Profile intelligence gathered could include potential passwords, personal and official email addresses, whether the user is a regular employee, a SOHO user, or a contractor.

Based on this harvested intelligence the infrastructure needed for the attack will be acquired, the course of action to successfully execute the campaign will be determined & evasion techniques that could be followed during the attack will be planned. New domains may be registered, command and control servers set up, exploits crafted, vulnerable employees identified, custom social engineering schemes plotted for these target employees, malicious files created, etc.
 
Recently, US airport workers from over 75 airports were targeted via malicious emails based on information such as their names, titles, and email addresses that were harvested via publicly-available documents [1].

Fig.1 shows how a simple search engine query can divulge information like emails exchanged between personnel in public forums which may seem innocuous, but can be used to launch a spear phishing attack. Popular mailing lists mask this sensitive information to avoid it from being scraped and abused by bots. Valid users on the other hand are allowed access after solving a simple CAPTCHA.

Fig.1: Search result revealing email addresses and other information about employees of an organization.

Prevention/Detection

Most of the intelligence collected by the assailants during this stage is publicly available and in general doesn’t involve the attackers touching any of the internal systems. Information that was gathered from previous APT campaigns but applicable to the current one could also be reused. This makes detecting an APT during these early stages of the attack challenging.

Usual best security practices such as conducting periodic penetration tests, hardening the applications & the operating systems, etc. are still relevant, but these measures by themselves don’t stand a chance against this adversary.

Organizations should take care to both restrict the amount of information that is flowing outside and be aware of publicly available sensitive information which could potentially be used against them.

Profile Scraper

Automated bots can be used to collect publicly available information on the company, the employees, etc. from popular social networking sites and search engines, etc. The data collected can automatically be analyzed for potential sensitive leaks.

Honey Profiles

Fake profiles at different organizational levels meant to be trip wires can be set up on popular social networking sites and connection attempts and profile hits can be analyzed. This could allow organizations to both recognize if they are being targeted and predict which individual or group of individuals are being targeted.

Click here to read the second part of this blog.

References:
1] http://www.seculert.com/blog/2014/07/extended-apt-campaign-targeted-us-airports.html

Images courtesy of google.com

Lokesh Kumar
Manager, K7 Threat Control Lab

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