CVE-2018-6952 in Patch
Summary
by MITRE
A double free exists in the another_hunk function in pch.c in GNU patch through 2.7.6.
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Analysis
by VulDB Data Team • 02/06/2023
The vulnerability identified as CVE-2018-6952 represents a critical double free condition within the GNU patch utility version 2.7.6 and earlier. This flaw exists in the another_hunk function located in the pch.c source file, which is part of the patch command-line tool used extensively for applying diffs to files. The double free vulnerability occurs when memory allocated for processing patch hunks is freed twice during the execution flow, creating a potential for arbitrary code execution or denial of service conditions. This issue is particularly concerning because GNU patch is a fundamental utility present in virtually all Unix-like operating systems and is frequently used in automated build processes, package management systems, and security updates.
The technical nature of this vulnerability stems from improper memory management within the patch utility's hunk processing logic. When GNU patch encounters a patch file with specific characteristics, the another_hunk function fails to properly track memory allocations, leading to a scenario where the same memory block gets deallocated twice. This double free condition can be exploited by an attacker who crafts a malicious patch file that triggers this specific code path. The vulnerability is classified under CWE-415 as Double Free, which is a well-known memory safety issue that can lead to heap corruption and potentially arbitrary code execution. The flaw is particularly dangerous because it occurs during the normal patch application process, meaning legitimate patch operations could be exploited without requiring special privileges or unusual circumstances.
The operational impact of CVE-2018-6952 extends far beyond simple denial of service, as it can enable remote code execution when GNU patch is used in automated environments or when users apply untrusted patches. Attackers could craft specially formatted patch files that, when processed by vulnerable versions of GNU patch, would trigger the double free condition and potentially allow for privilege escalation or system compromise. This vulnerability affects systems where GNU patch is used in package management, security update mechanisms, and continuous integration pipelines. The risk is heightened because patch utilities are often invoked with elevated privileges during system updates, making successful exploitation potentially catastrophic. The vulnerability also aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter, as it could enable attackers to execute arbitrary commands through compromised patch processing.
Mitigation strategies for this vulnerability primarily focus on immediate patching of affected GNU patch versions to 2.7.7 or later, which contain the necessary memory management fixes. System administrators should prioritize updating all instances of GNU patch across their infrastructure, particularly in environments where untrusted patch files might be processed. Additional protective measures include implementing strict input validation for patch files, using sandboxed environments for patch application, and monitoring for unusual patch processing activities. Organizations should also consider implementing automated patch management systems to ensure timely deployment of security updates. The fix typically involves proper memory allocation tracking and ensuring that freed memory blocks are not reused in the same execution path, preventing the double free condition from occurring. Security teams should also conduct vulnerability assessments to identify systems running vulnerable versions of GNU patch and prioritize remediation efforts based on risk exposure and system criticality.