CVE-2025-27091
Published: 20 February 2025
Summary
CVE-2025-27091 is a high-severity Heap-based Buffer Overflow (CWE-122) vulnerability in Cisco Openh264. Its CVSS base score is 8.6 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Client Execution (T1203); ranked in the top 14.4% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and SI-10 (Information Input Validation).
Deeper analysis
OpenH264 is a codec library supporting H.264 encoding and decoding in both SVC and AVC modes. CVE-2025-27091 is a heap overflow vulnerability in its decoding functions that stems from a race condition between Sequence Parameter Set memory allocation and subsequent non-IDR NAL unit memory usage. The flaw affects all releases through 2.5.0 and is assigned CVSS 8.6 under CWE-122 and CWE-787.
A remote unauthenticated attacker can exploit the issue by crafting a malicious bitstream and inducing a victim to process it in an affected decoder client. Successful exploitation can produce an unexpected crash or allow arbitrary commands to be executed on the victim host through abuse of the heap overflow.
The official Cisco OpenH264 security advisory and release notes for version 2.6.0 state that the vulnerability is resolved in that and later releases, with no known workarounds available. Users are directed to upgrade, and further details are available via the project GitHub repository or by contacting oss-security@cisco.com and psirt@cisco.com.
EPSS remains flat at a low value of 0.0247 with no material increase after disclosure.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-5088
Vulnerability details
OpenH264 is a free license codec library which supports H.264 encoding and decoding. A vulnerability in the decoding functions of OpenH264 codec library could allow a remote, unauthenticated attacker to trigger a heap overflow. This vulnerability is due to a…
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race condition between a Sequence Parameter Set (SPS) memory allocation and a subsequent non Instantaneous Decoder Refresh (non-IDR) Network Abstraction Layer (NAL) unit memory usage. An attacker could exploit this vulnerability by crafting a malicious bitstream and tricking a victim user into processing an arbitrary video containing the malicious bistream. An exploit could allow the attacker to cause an unexpected crash in the victim's user decoding client and, possibly, perform arbitrary commands on the victim's host by abusing the heap overflow. This vulnerability affects OpenH264 2.5.0 and earlier releases. Both Scalable Video Coding (SVC) mode and Advanced Video Coding (AVC) mode are affected by this vulnerability. OpenH264 software releases 2.6.0 and later contained the fix for this vulnerability. Users are advised to upgrade. There are no known workarounds for this vulnerability. ### For more information If you have any questions or comments about this advisory: * [Open an issue in cisco/openh264](https://github.com/cisco/openh264/issues) * Email Cisco Open Source Security ([oss-security@cisco.com](mailto:oss-security@cisco.com)) and Cisco PSIRT ([psirt@cisco.com](mailto:psirt@cisco.com)) ### Credits: * **Research:** Octavian Guzu and Andrew Calvano of Meta * **Fix ideation:** Philipp Hancke and Shyam Sadhwani of Meta * **Fix implementation:** Benzheng Zhang (@BenzhengZhang) * **Release engineering:** Benzheng Zhang (@BenzhengZhang)
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Heap overflow in OpenH264 decoder enables remote code execution via crafted malicious video bitstream processed by victim client application, directly mapping to Exploitation for Client Execution.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly requires timely remediation of known software flaws by patching OpenH264 to version 2.6.0 or later, eliminating the heap overflow race condition.
Implements memory safeguards such as address space layout randomization and non-executable heap to mitigate exploitation of the heap overflow for arbitrary command execution.
Validates malformed H.264 bitstreams containing crafted SPS and non-IDR NAL units before decoding to prevent triggering the race condition.