CVE-2021-45261 in Patch
Summary
by MITRE • 12/22/2021
An Invalid Pointer vulnerability exists in GNU patch 2.7 via the another_hunk function, which causes a Denial of Service.
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Analysis
by VulDB Data Team • 02/17/2026
The vulnerability CVE-2021-45261 represents a critical invalid pointer dereference issue within GNU patch version 2.7 that manifests through the another_hunk function. This flaw constitutes a denial of service vulnerability that can be exploited by malicious actors to disrupt the normal operation of systems relying on patch processing. The GNU patch utility serves as a fundamental tool for applying software patches and modifications, making this vulnerability particularly concerning for system administrators and security professionals who depend on reliable patch management processes. The vulnerability arises from improper memory handling within the patch processing logic, specifically when the utility encounters certain malformed patch files or edge cases during the hunk application process.
The technical implementation of this vulnerability stems from inadequate input validation and memory management within the another_hunk function which processes patch hunks during the patch application. When GNU patch encounters malformed input or specific combinations of patch data, the function fails to properly validate pointer references before dereferencing them, leading to a crash condition. This invalid pointer dereference can be triggered through carefully crafted patch files that exploit the boundary conditions within the patch processing engine. The vulnerability falls under the CWE-476 category of NULL Pointer Dereference, which is classified as a common weakness in software security practices. Attackers can leverage this weakness by providing malicious patch files that cause the application to crash, effectively rendering the patch utility unusable and potentially disrupting system update processes.
The operational impact of CVE-2021-45261 extends beyond simple denial of service, as it can significantly compromise system integrity and availability within environments that rely heavily on automated patch management. Systems utilizing GNU patch for regular updates, including enterprise environments, open source projects, and automated deployment pipelines, may experience service disruptions when encountering vulnerable patch files. The vulnerability can be particularly problematic in continuous integration environments where patch application is automated, as a single malicious patch could cause cascading failures across multiple systems. Additionally, the vulnerability may be exploited as part of broader attack chains where attackers first gain access to systems and then use the patched utility to maintain persistence or escalate privileges. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving privilege escalation and defense evasion, as it can be used to disrupt system operations and potentially hide malicious activities.
Mitigation strategies for CVE-2021-45261 should prioritize immediate patching of affected GNU patch installations to the latest available versions that contain the necessary fixes for the invalid pointer dereference. System administrators should implement strict input validation for all patch files before processing them through the GNU patch utility, particularly in automated environments where patch files may originate from untrusted sources. Network segmentation and access controls should be implemented to limit exposure of systems running GNU patch to potentially malicious inputs. Organizations should also consider implementing monitoring solutions that can detect abnormal patch utility behavior or crashes that may indicate exploitation attempts. The vulnerability highlights the importance of maintaining up-to-date software libraries and the necessity of thorough security testing for core system utilities. Regular security assessments of patch management processes and automated update systems are essential to prevent exploitation of similar vulnerabilities in other system components.