CVE-2014-7187 in Mac OS X
Summary
by MITRE
Off-by-one error in the read_token_word function in parse.y in GNU Bash through 4.3 bash43-026 allows remote attackers to cause a denial of service (out-of-bounds array access and application crash) or possibly have unspecified other impact via deeply nested for loops, aka the "word_lineno" issue.
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Analysis
by VulDB Data Team • 11/30/2024
The vulnerability identified as CVE-2014-7187 represents a critical off-by-one error within the GNU Bash shell's parsing mechanism, specifically in the read_token_word function located in the parse.y file. This flaw exists in bash versions through 4.3 bash43-026 and demonstrates how seemingly minor programming errors can lead to significant security implications. The issue stems from improper boundary checking when processing nested loop structures, creating a scenario where array access operations exceed their allocated memory boundaries.
The technical implementation of this vulnerability exploits the word_lineno variable handling within bash's parser to create a condition where deeply nested for loops can trigger an out-of-bounds array access. When bash encounters extremely nested loop constructs, the parser fails to properly manage the line number tracking mechanism, causing it to access memory locations beyond the allocated array bounds. This error manifests as a segmentation fault or application crash, effectively enabling a denial of service attack against systems running vulnerable bash versions.
From an operational perspective, this vulnerability presents a substantial risk to system availability and stability. Attackers can remotely trigger the flaw by crafting specially formatted shell scripts containing deeply nested for loops, leading to service disruption across affected systems. The impact extends beyond simple denial of service as the vulnerability may potentially enable arbitrary code execution depending on the system configuration and memory layout. The vulnerability aligns with CWE-129, which addresses improper validation of array indices, and represents a classic example of how buffer overflows can occur in parsing contexts.
The attack vector for CVE-2014-7187 typically involves remote exploitation through crafted input that gets processed by bash, making it particularly dangerous in web applications, automated systems, or any environment where bash processes untrusted input. Systems running vulnerable bash versions are susceptible to this attack regardless of network exposure, as the vulnerability is triggered during shell parsing operations. The flaw's classification under the ATT&CK framework would fall under T1059.001 for Command and Scripting Interpreter, specifically targeting bash execution environments.
Mitigation strategies for this vulnerability require immediate patching of affected bash installations to version 4.3 bash43-026 or later, which contains the necessary fixes for the boundary checking logic. Organizations should also implement input validation measures to prevent processing of suspiciously nested loop structures, particularly in environments where bash handles untrusted user input. Network segmentation and access controls can help limit the potential impact of exploitation attempts, while regular security audits should verify that all bash installations are properly updated and monitored for similar parsing vulnerabilities. The fix implemented in patched versions addresses the core issue by correcting the array boundary validation in the word_lineno tracking mechanism, preventing the out-of-bounds access condition that previously enabled the denial of service and potential code execution scenarios.