CVE-2025-68973 in GnuPG
Summary
by MITRE • 12/28/2025
In GnuPG before 2.4.9, armor_filter in g10/armor.c has two increments of an index variable where one is intended, leading to an out-of-bounds write for crafted input. (For ExtendedLTS, 2.2.51 and later are fixed versions.)
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Analysis
by VulDB Data Team • 01/25/2026
The vulnerability identified as CVE-2025-68973 affects GnuPG versions prior to 2.4.9, specifically within the armor_filter function located in g10/armor.c. This flaw represents a classic buffer management error that could potentially allow attackers to execute arbitrary code or cause denial of service conditions. The issue manifests as an out-of-bounds write operation that occurs when processing crafted input data through the armor filtering mechanism used in GnuPG's handling of OpenPGP messages.
The technical root cause involves a programming error where an index variable undergoes two increment operations instead of the intended single increment during the processing of armored data. This type of flaw falls under CWE-129, which addresses insufficient validation of length of input buffers, and more specifically relates to CWE-787, which covers out-of-bounds write conditions. The vulnerability is particularly concerning because it occurs within the core armor processing functionality that handles the conversion of binary OpenPGP data into ASCII-armored format, a fundamental operation in GnuPG's message handling pipeline.
When an attacker crafts malicious input data designed to exploit this double increment flaw, the system processes the data through the armor_filter function where the index variable becomes misaligned with the actual buffer boundaries. This misalignment results in writing data beyond the allocated memory space, potentially corrupting adjacent memory regions or allowing for memory corruption that could be exploited to execute arbitrary code. The vulnerability affects not only the standard 2.4.9 release but also the ExtendedLTS branch where versions 2.2.51 and later have been patched to address this specific issue.
The operational impact of this vulnerability extends beyond simple memory corruption as it could enable attackers to manipulate the execution flow of GnuPG applications. The out-of-bounds write condition creates opportunities for attackers to inject malicious code into memory locations adjacent to the affected buffer, potentially leading to privilege escalation or complete system compromise. Given that GnuPG is widely used for email encryption and digital signatures across enterprise and individual security implementations, this vulnerability poses a significant risk to organizations relying on proper cryptographic operations. The attack vector requires the victim to process crafted OpenPGP data through GnuPG, making it a targeted vulnerability that could be exploited in scenarios involving untrusted message processing.
Mitigation strategies should prioritize immediate deployment of patched versions, specifically GnuPG 2.4.9 or later for standard releases and 2.2.51 or later for ExtendedLTS installations. System administrators should implement strict input validation procedures for any OpenPGP data processing, particularly when handling untrusted messages from external sources. Additional defensive measures include deploying network segmentation to limit exposure, implementing sandboxing for GnuPG operations, and establishing monitoring procedures to detect anomalous memory access patterns. The vulnerability demonstrates the critical importance of thorough code review processes, particularly for memory management operations, and aligns with ATT&CK technique T1059.007 for executing commands through scripting languages where the memory corruption could be leveraged for command execution. Organizations should also consider implementing automated patch management systems to ensure rapid deployment of security updates and maintain updated threat intelligence feeds to monitor for related exploitation attempts.