CVE-2011-3946 in FFmpeg
Summary
by MITRE
The ff_h264_decode_sei function in libavcodec/h264_sei.c in FFmpeg before 0.10 allows remote attackers to have an unspecified impact via crafted Supplemental enhancement information (SEI) data, which triggers an infinite loop.
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Analysis
by VulDB Data Team • 01/11/2022
The vulnerability identified as CVE-2011-3946 represents a critical security flaw within the FFmpeg multimedia framework that affects the handling of H.264 video streams. This issue resides in the ff_h264_decode_sei function located within the libavcodec/h264_sei.c file, which processes Supplemental Enhancement Information data that is commonly embedded within H.264 video streams. The vulnerability manifests when maliciously crafted SEI data is processed by the decoder, leading to an exploitable condition that can be leveraged by remote attackers to disrupt normal system operations. The flaw specifically creates an infinite loop condition that can cause denial of service scenarios, making it particularly dangerous in environments where continuous media processing is required.
The technical implementation of this vulnerability stems from inadequate input validation within the SEI processing logic of the H.264 decoder. When the ff_h264_decode_sei function encounters malformed SEI data, it fails to properly handle the edge cases that would normally be caught during standard parsing procedures. This failure results in the decoder entering an infinite loop where it continuously processes the same invalid data without proper termination conditions. The vulnerability is classified under CWE-835, which specifically addresses the issue of infinite loops in software implementations. The attack vector requires an attacker to craft specially designed SEI data that, when embedded in an H.264 stream, will trigger the problematic code path in the decoder. This type of vulnerability is particularly concerning because SEI data is often used for various purposes including frame timing information, user data, and other enhancement features that are routinely processed by video decoders.
The operational impact of CVE-2011-3946 extends beyond simple denial of service scenarios to potentially affect critical multimedia applications and services. Systems that rely on FFmpeg for video processing, streaming services, media servers, and content delivery networks become vulnerable to exploitation. When an attacker successfully triggers this infinite loop condition, the affected system may consume excessive CPU resources, leading to system instability, performance degradation, or complete service unavailability. The vulnerability can be particularly devastating in server environments where multiple concurrent video streams are processed, as it can effectively render the entire system unusable. Additionally, this vulnerability aligns with ATT&CK technique T1499.004, which covers "Utilities: System Shutdown/Reboot" through resource exhaustion attacks that can be achieved via denial of service conditions. The impact is further amplified because many applications and services automatically process video content from untrusted sources, making exploitation relatively straightforward for attackers who can craft malicious media files.
Mitigation strategies for this vulnerability require immediate application of security patches and updates to FFmpeg versions that address the specific infinite loop condition in the SEI processing code. Organizations should prioritize updating their FFmpeg installations to versions 0.10 or later, which contain the necessary fixes to properly validate SEI data and prevent the infinite loop scenario. Additionally, implementing input validation measures at the application level can provide an additional layer of protection by filtering or rejecting suspicious SEI data before it reaches the vulnerable decoder functions. Network-level controls such as content filtering and media validation can also help prevent malicious SEI data from reaching vulnerable systems. Security monitoring should include detection of abnormal CPU usage patterns that may indicate exploitation attempts, and system administrators should implement proper resource limits and timeouts to prevent complete system exhaustion. The vulnerability demonstrates the importance of robust input validation in multimedia processing libraries and highlights the need for comprehensive testing of edge cases in codec implementations. Organizations should also consider implementing network segmentation and access controls to limit exposure to potentially malicious media content, particularly in environments where untrusted users can upload or stream content.