CVE-2011-3973 in FFmpeg
Summary
by MITRE
cavsdec.c in libavcodec in FFmpeg before 0.7.4 and 0.8.x before 0.8.3 allows remote attackers to cause a denial of service (incorrect write operation and application crash) via an invalid bitstream in a Chinese AVS video (aka CAVS) file, related to the decode_residual_block, check_for_slice, and cavs_decode_frame functions, a different vulnerability than CVE-2011-3362.
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Analysis
by VulDB Data Team • 11/21/2021
The vulnerability identified as CVE-2011-3973 represents a critical denial of service flaw within the FFmpeg multimedia framework's libavcodec library. This issue specifically affects the Chinese AVS video codec implementation and manifests when processing malformed bitstream data within CAVS video files. The vulnerability exists in versions prior to 0.7.4 for the 0.7.x release line and before 0.8.3 for the 0.8.x release line, making it a widespread concern affecting numerous systems that rely on FFmpeg for video processing operations.
The technical root cause of this vulnerability lies within three specific functions: decode_residual_block, check_for_slice, and cavs_decode_frame. These functions process different aspects of the CAVS video decoding pipeline and contain insufficient input validation mechanisms. When an attacker crafts a malicious CAVS video file with invalid bitstream data, the decoding functions attempt to perform incorrect write operations to memory locations that have not been properly allocated or validated. This incorrect memory manipulation leads to application crashes and system instability, effectively enabling a remote denial of service attack. The flaw operates at the codec level where the software fails to properly sanitize input data before processing, creating a condition where malformed data can trigger unexpected program behavior.
From an operational perspective, this vulnerability poses significant risks to systems that process multimedia content from untrusted sources. Web applications, media servers, content delivery networks, and any system that accepts user-uploaded video files become vulnerable to this attack vector. An attacker could exploit this vulnerability by uploading a malicious CAVS video file that, when processed by an affected FFmpeg installation, would cause the application to crash or become unresponsive. This type of attack could be particularly devastating in environments where multimedia processing is critical, such as streaming services, content management systems, or digital media applications. The vulnerability is classified under CWE-121 as a buffer overflow condition, specifically involving incorrect memory operations during video decoding processes.
The attack surface for this vulnerability extends beyond simple service disruption to potentially enable more sophisticated exploitation techniques. While the primary impact is denial of service, the incorrect write operations could theoretically be leveraged to execute arbitrary code under certain conditions, particularly if the affected system is running with insufficient memory protection mechanisms. Security researchers have noted that this vulnerability is distinct from CVE-2011-3362, indicating that it represents a separate code path with its own unique exploitation characteristics. The ATT&CK framework categorizes this vulnerability under the T1499.004 technique for 'Endpoint Denial of Service' and may also relate to T1595.001 for 'Network Denial of Service' when considering the broader impact on networked multimedia services.
Mitigation strategies for CVE-2011-3973 primarily focus on immediate version updates to FFmpeg releases that contain the necessary patches. System administrators should prioritize upgrading to FFmpeg versions 0.7.4 or 0.8.3 and later, which contain the specific fixes for the decode_residual_block, check_for_slice, and cavs_decode_frame functions. Additionally, implementing proper input validation and sanitization at the application level can provide defense-in-depth measures. Organizations should consider deploying intrusion detection systems that can identify and block suspicious multimedia file uploads, while also implementing content filtering mechanisms that validate file integrity before processing. Network-level mitigations include configuring firewalls to restrict access to multimedia processing services and implementing rate limiting to prevent abuse of video processing capabilities. The vulnerability underscores the importance of regular security updates and proper software maintenance practices, as well as the necessity of conducting thorough security testing on multimedia processing components to identify similar flaws in other codec implementations.