CVE-2020-20893 in FFmpeg
Summary
by MITRE • 09/20/2021
Buffer Overflow vulnerability in function activate in libavfilter/af_afade.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-2020-20893 resides within the FFmpeg multimedia framework's audio filtering component, specifically in the activate function located in libavfilter/af_afade.c. This flaw represents a critical security weakness that can be exploited by malicious actors to disrupt the normal operation of applications relying on FFmpeg for audio processing tasks. The vulnerability manifests when the software processes audio filter parameters without proper bounds checking, creating an opportunity for attackers to manipulate memory structures through crafted input data. Such buffer overflow conditions typically arise when programs write more data to a fixed-length buffer than it can accommodate, potentially leading to memory corruption and unpredictable system behavior. The affected version FFmpeg 4.2.1 demonstrates this weakness in its audio fade filter implementation, where the activate function fails to validate input parameters before processing them, creating a pathway for exploitation.
The technical implementation of this vulnerability stems from inadequate input validation within the audio filtering pipeline of FFmpeg. When the activate function processes audio fade parameters, it does not properly verify the size or content of incoming data structures, allowing attackers to supply malformed input that exceeds allocated buffer boundaries. This particular flaw falls under the CWE-121 CWE category, which specifically addresses stack-based buffer overflow conditions, though the actual memory corruption may occur in heap or other memory regions depending on the implementation details. The vulnerability's exploitation requires careful crafting of audio filter parameters that trigger the buffer overflow during the audio processing workflow, making it particularly dangerous in environments where FFmpeg is used to process untrusted media content from various sources. The attack surface expands when considering that many applications and services utilize FFmpeg as a core component for multimedia processing, including content management systems, streaming platforms, and media editing software.
The operational impact of CVE-2020-20893 extends beyond simple denial of service scenarios to potentially enable more sophisticated attack vectors within the broader ATT&CK framework. While the immediate effect may be system instability or application crashes, the underlying buffer overflow creates opportunities for privilege escalation or code execution in certain contexts. Attackers can leverage this vulnerability to cause service disruption across multiple applications that depend on FFmpeg, particularly in server environments where media processing is a common operation. The vulnerability's exploitation can result in complete system unavailability, data corruption, or in more severe cases, allow attackers to execute arbitrary code with the privileges of the affected process. This makes the vulnerability particularly dangerous in cloud environments, content delivery networks, or any infrastructure where FFmpeg is deployed to handle large volumes of incoming media data, as the impact can cascade across multiple services and users.
Mitigation strategies for CVE-2020-20893 should prioritize immediate software updates to FFmpeg versions that have addressed this buffer overflow vulnerability through proper input validation and memory boundary checks. Organizations should implement comprehensive patch management protocols to ensure all systems utilizing FFmpeg are updated with the latest security patches released by the FFmpeg development team. Additionally, input sanitization measures should be implemented at application layers that interface with FFmpeg, including parameter validation and length checking before passing audio filter data to the vulnerable function. Network-level protections such as intrusion detection systems can help identify exploitation attempts by monitoring for anomalous audio processing patterns or malformed input sequences. The implementation of memory protection mechanisms including stack canaries, address space layout randomization, and data execution prevention can provide additional defense-in-depth measures against exploitation attempts. Security teams should also consider implementing application whitelisting and sandboxing techniques to limit the potential impact of successful exploitation attempts, particularly in environments where FFmpeg is used to process untrusted user content. Regular security assessments and vulnerability scanning should be conducted to identify any remaining instances of the vulnerable FFmpeg versions within the organization's infrastructure.