CVE-2011-3937 in libav
Summary
by MITRE
The H.263 codec (libavcodec/h263dec.c) in FFmpeg 0.7.x before 0.7.12, 0.8.x before 0.8.11, and unspecified versions before 0.10, and in Libav 0.5.x before 0.5.9, 0.6.x before 0.6.6, 0.7.x before 0.7.5, and 0.8.x before 0.8.1 has unspecified impact and attack vectors related to "width/height changing with frame threads."
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Analysis
by VulDB Data Team • 12/21/2021
The vulnerability identified as CVE-2011-3937 represents a critical security flaw within the H.263 video codec implementation in both FFmpeg and Libav multimedia frameworks. This issue specifically affects versions prior to the mentioned secure releases, creating a potential attack surface that could be exploited by malicious actors. The vulnerability manifests in the handling of width and height parameters during frame processing when frame threading is enabled, creating a scenario where the codec's internal state management becomes inconsistent. The unspecified impact and attack vectors suggest that this weakness could potentially lead to various security consequences including denial of service, memory corruption, or even arbitrary code execution depending on the specific implementation details and exploitation conditions.
The technical root cause of this vulnerability lies in the improper handling of video frame dimensions when multiple threads process video frames simultaneously. When frame threading is enabled in the H.263 decoder, the codec must manage shared resources and state information across multiple execution threads. The flaw occurs during dynamic width and height parameter changes within the decoding process, where the thread synchronization mechanisms fail to properly account for these dimension changes. This creates a race condition or state inconsistency that can lead to memory access violations or buffer overflows. The vulnerability specifically affects the libavcodec/h263dec.c file in FFmpeg and similar implementations in Libav, where the codec's frame processing logic does not adequately protect against concurrent modification of frame dimension parameters. This issue falls under the CWE-367 weakness category, which describes Time-of-Check to Time-of-Use (TOCTOU) vulnerabilities, as the codec's behavior changes between the time when frame dimensions are checked and when they are actually used for processing.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, potentially enabling more sophisticated attacks depending on the execution environment. When exploited, this vulnerability could allow attackers to cause applications using these codecs to crash or behave unpredictably, effectively creating a denial of service condition that could affect media players, streaming servers, or any application that processes H.263 video content. In more severe cases, the memory corruption resulting from improper dimension handling could potentially be leveraged to execute arbitrary code, especially when the affected applications process untrusted video content from external sources. The vulnerability affects a wide range of multimedia applications and systems that rely on FFmpeg or Libav for video processing, making it particularly dangerous in environments where these libraries are widely deployed. The attack vectors are diverse and could include malicious video files, network-based streaming attacks, or even file upload vulnerabilities in web applications that process user-uploaded video content.
Mitigation strategies for this vulnerability should focus on immediate version updates to the patched releases of FFmpeg and Libav, as these contain the necessary fixes for the frame threading and dimension handling issues. Organizations should implement comprehensive patch management processes to ensure all systems using these libraries are updated promptly. Additionally, administrators should consider implementing input validation measures that restrict the types of video files processed, particularly those with dynamic dimension changes, and monitor for unusual resource consumption patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper thread synchronization in multimedia codecs and highlights the need for thorough testing of concurrent processing scenarios in media handling libraries. Security teams should also consider implementing sandboxing techniques for video processing applications and establishing network monitoring rules to detect potential exploitation attempts targeting this specific vulnerability. The ATT&CK framework categorizes this vulnerability under the T1203 - Exploitation for Client Execution tactic, as exploitation could lead to arbitrary code execution in vulnerable applications.