CVE-2014-6277 in Mac OS X
Summary
by MITRE
GNU Bash through 4.3 bash43-026 does not properly parse function definitions in the values of environment variables, which allows remote attackers to execute arbitrary code or cause a denial of service (uninitialized memory access, and untrusted-pointer read and write operations) via a crafted environment, as demonstrated by vectors involving the ForceCommand feature in OpenSSH sshd, the mod_cgi and mod_cgid modules in the Apache HTTP Server, scripts executed by unspecified DHCP clients, and other situations in which setting the environment occurs across a privilege boundary from Bash execution. NOTE: this vulnerability exists because of an incomplete fix for CVE-2014-6271 and CVE-2014-7169.
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Analysis
by VulDB Data Team • 11/18/2024
The vulnerability described in CVE-2014-6277 represents a critical security flaw in GNU Bash that emerged from an incomplete remediation of previously discovered vulnerabilities. This issue affects Bash versions through 4.3 bash43-026 and stems from improper parsing of function definitions within environment variable values, creating a fundamental weakness in how the shell handles untrusted input. The vulnerability specifically exploits the way Bash processes environment variables that contain function definitions, leading to potential code execution or denial of service conditions. The flaw manifests when environment variables containing specially crafted function definitions are processed by Bash, particularly in contexts where environment setting occurs across privilege boundaries, making it particularly dangerous in server environments and network services.
The technical implementation of this vulnerability involves uninitialized memory access and untrusted pointer read and write operations that occur during Bash's environment variable parsing process. When Bash encounters an environment variable containing a function definition, it fails to properly validate or sanitize the input before executing the code within that definition. This improper parsing creates a situation where maliciously crafted environment variables can trigger arbitrary code execution, effectively allowing remote attackers to execute commands with the privileges of the affected process. The vulnerability is particularly insidious because it operates at the shell level, meaning that any application or service that invokes Bash with untrusted environment variables becomes susceptible to exploitation.
The operational impact of CVE-2014-6277 extends across multiple critical systems and services that rely on Bash for command execution. The vulnerability has been demonstrated to affect OpenSSH sshd through the ForceCommand feature, where maliciously crafted environment variables can be used to execute arbitrary commands on target systems. Additionally, the flaw impacts Apache HTTP Server modules mod_cgi and mod_cgid, where CGI scripts can be exploited to execute malicious code. DHCP clients that invoke Bash also present potential attack vectors, as these clients often execute scripts with environment variables set by network infrastructure. The vulnerability's widespread applicability stems from Bash's prevalence in Unix-like systems and the common practice of using Bash to execute scripts in environments where environment variables may contain untrusted data, creating a significant attack surface that spans from network services to system utilities.
The remediation of this vulnerability requires comprehensive patching of affected Bash versions, with particular attention to the incomplete fix that was initially applied to address CVE-2014-6271 and CVE-2014-7169. Organizations must ensure that all systems running Bash versions through 4.3 bash43-026 are updated to patched versions that properly handle environment variable parsing and function definition validation. System administrators should also implement strict environment variable validation and sanitization practices, particularly for applications that set environment variables in contexts where privilege escalation could occur. The vulnerability aligns with CWE-122 (Heap Overflow) and CWE-787 (Out-of-bounds Write) categories, representing a classic case of improper input validation leading to arbitrary code execution. From an ATT&CK framework perspective, this vulnerability maps to T1059.001 (Command and Scripting Interpreter: Bash) and T1068 (Exploitation for Privilege Escalation), emphasizing its role in both command execution and privilege escalation scenarios that attackers can leverage for persistent access to compromised systems.