CVE-2012-3410 in ILOM
Summary
by MITRE
Stack-based buffer overflow in lib/sh/eaccess.c in GNU Bash before 4.2 patch 33 might allow local users to bypass intended restricted shell access via a long filename in /dev/fd, which is not properly handled when expanding the /dev/fd prefix.
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Analysis
by VulDB Data Team • 03/05/2019
The vulnerability identified as CVE-2012-3410 represents a critical stack-based buffer overflow within the GNU Bash shell utility affecting versions prior to 4.2 patch 33. This flaw resides in the lib/sh/eaccess.c source file and specifically targets the handling of filenames that begin with the /dev/fd prefix. The issue arises from inadequate input validation when Bash processes file paths that reference the /dev/fd filesystem interface, which provides access to file descriptors through symbolic links. When a malicious user supplies an excessively long filename in the /dev/fd path, the shell fails to properly validate the length of the expanded path, leading to a buffer overflow condition on the stack.
The technical implementation of this vulnerability demonstrates a classic stack overflow scenario where the program writes data beyond the bounds of a fixed-size buffer allocated on the stack. The /dev/fd filesystem interface in Unix-like operating systems allows processes to access file descriptors through symbolic links, with /dev/fd/n representing file descriptor n. When Bash encounters a path beginning with /dev/fd, it attempts to expand this prefix into an actual file path, but the expansion process does not properly enforce length limits on the resulting path string. This oversight creates an opportunity for attackers to craft malicious input that exceeds the buffer capacity, potentially leading to arbitrary code execution or system compromise.
The operational impact of this vulnerability extends beyond simple privilege escalation as it specifically targets restricted shell environments where users should be limited in their system access. In restricted shell contexts, users are typically confined to specific commands and directories to prevent unauthorized system access. However, this buffer overflow allows local users to bypass these intended restrictions by exploiting the flawed path expansion mechanism. The vulnerability is particularly dangerous in environments where restricted shells are used for security purposes, such as in chroot jails, limited user accounts, or when implementing security controls around sensitive system areas. Attackers can leverage this flaw to gain elevated privileges or execute arbitrary commands within the restricted environment, effectively neutralizing the security controls that were designed to prevent such access.
The exploitation of this vulnerability aligns with several ATT&CK framework techniques including privilege escalation and defense evasion. Specifically, it maps to techniques such as T1068 (Local Privilege Escalation) and T1059 (Command and Scripting Interpreter) where attackers can leverage shell vulnerabilities to execute malicious commands. From a CWE perspective, this vulnerability corresponds to CWE-121, Stack-based Buffer Overflow, which describes a condition where a program writes data past the end of a buffer allocated on the stack. The flaw also relates to CWE-20, Improper Input Validation, as it demonstrates inadequate validation of input parameters during path expansion. Additionally, this vulnerability exemplifies the broader category of CWE-787, Out-of-bounds Write, where programs write data beyond the boundaries of allocated memory regions. The remediation approach for this vulnerability involves applying the official patch from GNU Bash version 4.2 patch 33, which implements proper bounds checking during /dev/fd path expansion. Organizations should also implement comprehensive patch management procedures to ensure all systems running Bash are updated promptly, as this vulnerability affects a core system component with widespread deployment across Unix-like operating systems.