CVE-2020-20897 in FFmpeg
Summary
by MITRE • 09/20/2021
Buffer Overflow vulnerability in function filter_slice in libavfilter/vf_bm3d.c in Ffmpeg 4.2.1, allows attackers to cause a Denial of Service or other unspecified impacts.
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Analysis
by VulDB Data Team • 09/29/2021
The buffer overflow vulnerability identified as CVE-2020-20897 resides within the ffmpeg media processing library, specifically in the filter_slice function located in the libavfilter/vf_bm3d.c file. This flaw manifests in version 4.2.1 of the ffmpeg software, representing a critical security weakness that can be exploited by malicious actors to disrupt system operations. The vulnerability stems from inadequate input validation within the video filtering component that processes motion compensation and noise reduction operations using the BM3D algorithm. When ffmpeg processes video streams containing specially crafted malicious input data through the affected filtering function, the software fails to properly bounds-check array allocations and memory operations, creating opportunities for buffer overflow conditions to occur.
The technical implementation of this vulnerability involves the filter_slice function failing to validate the size parameters of input data structures before performing memory operations. This function processes video frames during the BM3D denoising process where it handles temporal filtering operations across multiple video frames. The flaw occurs when the software attempts to allocate memory buffers based on user-supplied parameters without proper verification of their legitimacy. According to CWE-121, this represents a classic stack-based buffer overflow condition where insufficient bounds checking allows attackers to overwrite adjacent memory locations. The vulnerability can be triggered through various attack vectors including malicious video files, malformed media streams, or crafted input parameters passed to ffmpeg during video processing operations.
The operational impact of CVE-2020-20897 extends beyond simple denial of service conditions to potentially enable more severe consequences including arbitrary code execution and system compromise. When exploited successfully, this vulnerability can cause ffmpeg processes to crash and terminate unexpectedly, leading to service disruption for applications relying on the media processing capabilities. However, the potential for more sophisticated exploitation exists, as the buffer overflow condition may allow attackers to manipulate program execution flow through stack corruption. Systems utilizing ffmpeg for video processing, transcoding, or streaming operations become vulnerable to this attack vector, particularly those processing untrusted media content from external sources. The vulnerability affects various deployment scenarios including web applications, media servers, content management systems, and video processing pipelines that depend on ffmpeg's filtering capabilities.
Mitigation strategies for CVE-2020-20897 should prioritize immediate software updates to versions of ffmpeg that have addressed this vulnerability through proper bounds checking and memory validation. Organizations should implement comprehensive input validation measures for all media processing workflows and consider deploying sandboxed execution environments for video processing tasks. Network-based mitigations including content filtering and media validation procedures can help reduce exposure to malformed input streams. Security monitoring should be enhanced to detect unusual ffmpeg process behavior, memory allocation patterns, or unexpected termination events that may indicate exploitation attempts. Additionally, implementing principle of least privilege access controls for ffmpeg processes and regular security assessments of media processing workflows will help reduce the attack surface. According to ATT&CK framework, this vulnerability maps to T1203 - Exploitation for Client Execution and T1499 - Endpoint Termination, highlighting the need for both defensive measures and incident response capabilities. Regular patch management programs should be established to ensure all ffmpeg installations remain current with security fixes, particularly in environments processing external media content where the risk of exploitation is highest.