CVE-2012-2796 in FFmpeg
Summary
by MITRE
Unspecified vulnerability in the vc1_decode_frame function in libavcodec/vc1dec.c in FFmpeg before 0.11 and Libav 0.8.x before 0.8.4 has unknown impact and attack vectors, related to inconsistencies in "coded slice positions and interlacing" that trigger "out of array writes."
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Analysis
by VulDB Data Team • 12/13/2021
The vulnerability identified as CVE-2012-2796 represents a critical memory corruption flaw within the FFmpeg multimedia framework's video decoding component. This issue specifically affects the vc1_decode_frame function located in libavcodec/vc1dec.c, which processes VC-1 video streams. The vulnerability exists in FFmpeg versions prior to 0.11 and Libav versions prior to 0.8.4, making it a widespread concern across numerous multimedia applications that rely on these libraries for video processing capabilities. The flaw stems from inconsistencies in how the decoder handles coded slice positions and interlacing parameters during video frame reconstruction, creating a scenario where the decoder fails to properly validate input data boundaries.
The technical nature of this vulnerability manifests as out-of-bounds memory writes that occur when the VC-1 decoder encounters malformed or maliciously crafted video data. During the decoding process, the function fails to properly validate the relationship between coded slice positions and interlacing information, allowing attackers to manipulate the decoder's internal state through carefully constructed input streams. This inconsistency creates a condition where the decoder attempts to write data beyond the allocated memory boundaries of its internal buffers, potentially leading to memory corruption that can be exploited for arbitrary code execution. The vulnerability operates at the intersection of multiple CWE categories including CWE-121 heap-based buffer overflow and CWE-787 out-of-bounds write, making it particularly dangerous in multimedia processing environments where untrusted input is commonly processed.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can potentially enable remote code execution when exploited in applications that process untrusted video content. Attackers can craft malicious VC-1 video streams that trigger the out-of-bounds write conditions, potentially allowing them to overwrite critical memory locations including return addresses, function pointers, or other control structures. This vulnerability is particularly concerning in web browsers, media players, and server applications that automatically decode video content from untrusted sources. The attack vectors are diverse and include web-based exploitation through embedded video content, email attachments, or streaming media services that utilize FFmpeg or Libav for video processing. The vulnerability's exploitation requires careful crafting of input data to trigger the specific conditions that lead to memory corruption, making it a sophisticated target for advanced persistent threats.
Mitigation strategies for CVE-2012-2796 primarily involve immediate software updates to patched versions of FFmpeg and Libav where the vulnerability has been addressed through proper input validation and boundary checking mechanisms. Organizations should implement comprehensive patch management procedures to ensure all systems utilizing these libraries receive updates promptly. Additional protective measures include input validation at application level, sandboxing of multimedia processing components, and network segmentation to limit exposure to potentially malicious content. Security researchers have noted that this vulnerability aligns with ATT&CK techniques related to code injection and memory corruption attacks, emphasizing the need for defensive measures that focus on input sanitization and runtime protection. The fix typically involves implementing proper bounds checking for slice position calculations and ensuring that interlacing parameters are validated before being used in memory allocation operations, thereby preventing the out-of-bounds writes that lead to exploitable conditions.