External risk intelligence

GNU Bash Remote Code Execution Vulnerability.

CVE advisoryKnown Exploit

CVE-2014-6271

The vulnerability exists in Bash, a core component often invoked by internet-facing services such as web servers (via CGI/mod_cgi) and remote access gateways (via sshd/ForceCommand). Because these services are commonly deployed as edge-facing entry points, the vulnerable execution path is frequently reachable from the public internet.

OS Command Injection

Gnu Bash

4.3 and earlier4.9.0 to before 4.9.124.10.0 to before 4.10.94.11.0 to before 4.11.114.12.0 to before 4.12.94.13.0 to before 4.13.94.14.0 to before 4.14.4f456before 4.1.14.1.1;...

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This vulnerability affects the GNU Bash shell, a common command-line interpreter. It allows attackers to execute arbitrary code by manipulating environment variables. This can lead to unauthorized access and control over affected systems.

Vulnerable: GNU Bash shell
Flaw: Allows arbitrary code execution
Impact: System compromise

Attack Path

How an attacker could exploit the issue

Bash versions through 4.3 contain a flaw in how they process environment variables. This allows attackers to execute arbitrary code by sending specially crafted environment variables. Systems using Bash in certain configurations, such as web servers with CGI or SSH servers with ForceCommand, are particularly susceptible.

Exposure condition: Network access to vulnerable Bash.
Attacker starting point: Unauthenticated network access.
Trigger and result: Crafted environment variable; arbitrary code execution.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability, discovered in GNU Bash, allows remote attackers to execute arbitrary code by exploiting how Bash processes environment variables. This could lead to unauthorized access and control of affected systems. The broad impact and ease of exploitation make this a significant risk.

Attacker skill level: Low
Access required: Network access
Business risk or urgency: High

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability allows for arbitrary code execution due to how GNU Bash processes environment variables. Organizations may face risks to systems, data, and operations if this vulnerability is exploited. A systematic approach is recommended to address the potential impact.

Find affected assets.
Reduce exposure or isolate risk.
Fix, verify, and monitor.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

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Frequently asked questions

What is the GNU Bash Remote Code Execution Vulnerability?

The GNU Bash Remote Code Execution Vulnerability, also known as "ShellShock," is a critical flaw in the Bash shell (versions through 4.3). It allows remote attackers to execute arbitrary code by crafting environment variables. This can lead to unauthorized access and control over affected systems by exploiting configurations like web servers or SSH.

How does the GNU Bash vulnerability (CVE-2014-6271) allow for code execution?

This vulnerability stems from how GNU Bash (versions through 4.3) processes trailing strings after function definitions within environment variable values. By providing a specially crafted environment variable, an attacker can trick Bash into executing arbitrary commands. This is often seen in scenarios where environment variables are set before Bash executes a script or command, such as through web server CGI scripts or SSH's ForceCommand feature.

What is the impact of the ShellShock vulnerability on systems?

The ShellShock vulnerability allows for arbitrary code execution, which can lead to a complete compromise of the affected system. Attackers can potentially gain unauthorized access, steal sensitive data, disrupt operations, or use the compromised system to launch further attacks. Its broad reach across many Linux and Unix-like systems makes it a significant threat.

What is the relevance of the "ShellShock" vulnerability (CVE-2014-6271) to internet-facing systems?

This vulnerability is highly relevant to internet-facing systems because Bash is often utilized by services that process external input, such as web servers via CGI and remote access solutions like SSH. Attackers can reach vulnerable Bash instances over the network, making systems exposed to the internet prime targets.

What steps should be taken to address the GNU Bash vulnerability?

To mitigate the risks associated with this vulnerability, it is crucial to apply updates to the GNU Bash shell provided by your operating system vendor. Regularly review system configurations for potential exposure points, especially those involving CGI scripts or SSH's ForceCommand. Implementing a robust vulnerability management program is essential for ongoing protection.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.