CVE-2011-3974 in FFmpeg
Summary
by MITRE
Integer signedness error in the decode_residual_inter function in 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, a different vulnerability than CVE-2011-3362.
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Analysis
by VulDB Data Team • 11/21/2021
The vulnerability described in CVE-2011-3974 represents a critical integer signedness error within the FFmpeg multimedia framework's video decoding component. This flaw exists specifically in the decode_residual_inter function located in the cavsdec.c file within libavcodec, affecting FFmpeg versions prior to 0.7.4 and 0.8.x versions before 0.8.3. The vulnerability manifests when processing Chinese AVS video files, which utilize the Audio Video Coding Standard encoding format. This particular issue is distinct from CVE-2011-3362, indicating it represents a separate class of vulnerabilities within the same software component. The flaw stems from improper handling of signed and unsigned integer operations during the decoding process, creating a condition where maliciously crafted bitstream data can trigger unexpected behavior in the application's memory management.
The technical implementation of this vulnerability involves an integer signedness error that occurs during the decoding of residual data in the Chinese AVS video format. When the decode_residual_inter function processes malformed input data, the improper handling of signed integer operations causes incorrect calculations that result in memory access violations. This type of error falls under the CWE-190 category of integer overflow and under CWE-129 for improper validation of array indices. The vulnerability specifically exploits how the decoder handles the signedness of integer variables when calculating memory offsets for writing residual data during video decompression. The incorrect write operation occurs because the signed integer arithmetic produces unexpected negative values that are then used as array indices or memory offsets, leading to memory corruption and subsequent application crash.
The operational impact of this vulnerability extends beyond simple denial of service, as it represents a potential vector for more sophisticated attacks within multimedia processing environments. Remote attackers can exploit this flaw by crafting specially designed CAVS video files that contain invalid bitstream data, which when processed by vulnerable FFmpeg implementations will cause the application to crash or behave unpredictably. This vulnerability affects any system that utilizes FFmpeg for video processing or playback, including web servers handling multimedia content, media streaming platforms, and desktop applications that depend on FFmpeg for video decoding. The vulnerability's remote exploitability means that attackers can potentially cause service disruption without requiring local system access, making it particularly concerning for server environments and applications that process untrusted multimedia content. According to ATT&CK framework, this vulnerability maps to T1203 - Exploitation for Client Execution and T1499 - Endpoint Denial of Service, as it enables adversaries to cause application instability and system resource exhaustion through crafted media files.
Mitigation strategies for CVE-2011-3974 primarily focus on immediate software updates and deployment of patched FFmpeg versions. System administrators should prioritize upgrading to FFmpeg versions 0.7.4 or 0.8.3 and later, which contain the necessary fixes for the integer signedness error. Additionally, implementing input validation measures that filter or reject suspicious video files before processing can provide an additional layer of protection. Network security controls such as content filtering and sandboxing of multimedia processing components can help prevent exploitation of this vulnerability in environments where updating software is not immediately possible. Organizations should also consider implementing automated vulnerability scanning tools that can detect the presence of vulnerable FFmpeg versions in their infrastructure and provide alerts for remediation. The fix for this vulnerability typically involves proper handling of signed integer operations and ensuring that calculated memory offsets remain within valid bounds, preventing the incorrect write operations that lead to application crashes and potential memory corruption scenarios.