CVE-2026-94287 in libXpm
Summary
by MITRE • 09/28/2026
A denial of service via unsigned underflow in libXpm's write path in libXpm before 3.5.19 could be used by local attackers to cause unbounded CPU usage and memory exhaustion.
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Analysis
by VulDB Data Team • 09/28/2026
The vulnerability identified within the X PixMap library, specifically prior to version 3.5.19, represents a critical flaw in the image writing subsystem that stems from improper handling of integer arithmetic operations during data serialization processes. This defect is classified under CWE-190 as an Integer Overflow or Wraparound issue, which manifests here through unsigned underflow conditions when processing specific malformed input files. The root cause lies in the failure to validate bounds and perform proper type checking before executing subtraction operations on size variables that are declared as unsigned integers. When a crafted XPM file contains dimensions or data lengths that result in a value smaller than zero during calculation, the unsigned integer wraps around to a very large positive number due to two's complement arithmetic rules inherent in C programming languages. This mathematical anomaly transforms what should be an error condition into a valid but catastrophically incorrect size parameter for subsequent memory allocation and copy operations.
From an operational perspective, this flaw allows local attackers with access to the system to trigger a denial of service against applications that utilize libXpm for rendering or manipulating X PixMap images. By supplying a specially crafted image file containing manipulated header values, an attacker can force the application to allocate excessive amounts of memory based on the wrapped-around size value rather than the actual data length. This leads directly to memory exhaustion as the system attempts to fulfill requests for buffers that are orders of magnitude larger than available resources. Concurrently, the processing loop associated with writing this oversized buffer consumes unbounded CPU cycles attempting to process or copy non-existent or garbage data until the operating system intervenes by terminating the application due to resource limits or out-of-memory conditions. This effectively renders any service relying on libXpm unavailable for legitimate users, disrupting workflows that depend on image processing capabilities within X11 environments.
The attack vector is primarily local, requiring an attacker to have user-level access to execute code or place files in directories accessible by the target application. While remote exploitation via network services displaying images would be ideal for attackers, the current description emphasizes local impact through file manipulation. This aligns with MITRE ATT&CK technique T1496, Resource Hijacking, where resources are consumed to degrade service availability rather than stealing data or gaining unauthorized access. The vulnerability highlights a common class of bugs in legacy graphics libraries that prioritize performance over rigorous input validation, particularly when dealing with binary formats like XPM that rely on precise header integrity for correct parsing.
Mitigation strategies must focus on immediate patching and defensive programming practices. Organizations should upgrade libXpm to version 3.5.19 or later where these integer underflow checks have been implemented by the maintainers. For systems unable to update immediately, runtime monitoring tools can be deployed to detect abnormal memory spikes associated with image processing applications. Additionally, developers integrating this library into custom software should implement strict input validation at the application layer before passing data to libXpm functions, ensuring that all dimension and length parameters are within expected bounds for standard XPM files. Security audits of legacy codebases using older versions of graphics libraries are recommended to identify similar unsigned integer arithmetic flaws across other image processing modules.