CVE-2026-54240 Overview
CVE-2026-54240 is an integer overflow vulnerability in libde265, an open source implementation of the H.265/HEVC video codec. Versions prior to 1.1.1 use signed 32-bit arithmetic to compute pixel offsets during decoding. A crafted HEVC stream with large image dimensions triggers the overflow and causes out-of-bounds heap reads or writes in the decoder. Successful exploitation can disclose memory contents, corrupt heap data, or crash applications that embed the library. The maintainers released 1.1.1 to address the issue. The weakness is tracked under CWE-190 (Integer Overflow or Wraparound).
Critical Impact
A malicious HEVC video processed by an application linked against libde265 can trigger heap memory corruption or information disclosure without user interaction beyond opening the file.
Affected Products
- libde265 versions prior to 1.1.1
- Applications and media pipelines that embed libde265 for HEVC decoding
- Downstream distributions packaging vulnerable libde265 releases
Discovery Timeline
- 2026-09-11 - CVE-2026-54240 published to the National Vulnerability Database
- 2026-09-14 - Last updated in NVD database
Technical Details for CVE-2026-54240
Vulnerability Analysis
The defect resides in libde265's pixel offset computation logic. The decoder uses signed 32-bit integers to calculate byte offsets into heap-allocated pixel buffers. When an HEVC stream declares large width, height, or stride values, the intermediate multiplication overflows the int32_t range and wraps around to a small or negative value. The decoder then treats the wrapped result as a valid offset and issues read or write operations against the pixel buffer.
Because the miscalculated offset points outside the intended allocation, the decoder accesses adjacent heap memory. Reads can leak sensitive process memory to attacker-influenced output, while writes can corrupt heap metadata or neighboring objects. The condition sits on the parsing path for standard HEVC frames, so no authentication is required to reach the vulnerable code.
Root Cause
The root cause is the use of signed 32-bit arithmetic for offset calculations that can legitimately exceed INT32_MAX for high-resolution HEVC content. The code lacks range checks and does not promote intermediate values to a wider integer type before multiplication. This matches the classic [CWE-190] pattern where attacker-controlled dimensions drive an unchecked arithmetic operation.
Attack Vector
Exploitation requires delivering a crafted HEVC bitstream to a target that decodes it with libde265. Delivery paths include websites that autoplay HEVC video, email attachments, messaging platforms, thumbnail generators, and media servers that transcode user-supplied content. The attack complexity is high because the attacker must shape dimensions and buffer layout to reach a useful memory corruption primitive, but no privileges or user interaction beyond media handling are required.
See the GitHub Security Advisory GHSA-ccfw-29x7-rrx3 for the maintainer's technical description and patch reference.
Detection Methods for CVE-2026-54240
Indicators of Compromise
- Crashes or segmentation faults in processes linked against libde265.so when processing untrusted HEVC content
- Heap corruption reports from AddressSanitizer or hardened allocators during video decoding
- HEVC files with anomalously large declared picture dimensions that exceed typical broadcast or streaming profiles
Detection Strategies
- Inventory all software using libde265 by scanning for the shared object and static links, then compare installed versions against 1.1.1
- Instrument media processing services with AddressSanitizer or MemorySanitizer in staging to catch out-of-bounds accesses on fuzzed HEVC input
- Monitor endpoint telemetry for unexpected child processes, crashes, or memory faults originating from video players, browsers, and thumbnail services
Monitoring Recommendations
- Alert on repeated decoder crashes tied to HEVC MIME types or .hevc, .h265, and .mp4 file handling
- Log and review HEVC transcoding jobs in server-side media pipelines for abnormal input dimensions
- Correlate media application crashes with subsequent process creation or network activity to identify post-exploitation behavior
How to Mitigate CVE-2026-54240
Immediate Actions Required
- Upgrade libde265 to version 1.1.1 or later across all endpoints, servers, and container images
- Rebuild and redeploy applications that statically link libde265 against the patched release
- Restrict HEVC decoding of untrusted content in server-side media pipelines until patches are deployed
Patch Information
The libde265 maintainers released version 1.1.1, which corrects the pixel offset arithmetic to prevent the integer overflow. Refer to the GitHub Security Advisory GHSA-ccfw-29x7-rrx3 for commit references and release notes. Linux distribution users should track their vendor's security tracker for backported package updates.
Workarounds
- Disable HEVC decoding in applications that expose the codec to untrusted input when patching is not immediately feasible
- Sandbox media decoding processes using seccomp, AppArmor, or SELinux profiles to limit the impact of memory corruption
- Enforce input size limits on uploaded media in transcoding services to reject streams with dimensions that trigger the overflow
# Verify installed libde265 version on Debian/Ubuntu
dpkg -l | grep libde265
# Verify installed libde265 version on RHEL/Fedora
rpm -q libde265
# Upgrade to a patched release (example, Debian/Ubuntu)
sudo apt update && sudo apt install --only-upgrade libde265-0
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
