CVE-2020-21690 in FFmpeg
Summary
by MITRE • 08/11/2021
A memory leak in the grow_array function in cmdutils.c og Ffmpeg 4.2 allows attackers to cause a denial of service (DOS) via a crafted ogg file.
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Analysis
by VulDB Data Team • 08/15/2021
The vulnerability identified as CVE-2020-21690 represents a critical memory management flaw within the FFmpeg multimedia framework version 4.2. This issue resides in the grow_array function located within the cmdutils.c source file, demonstrating a classic memory leak condition that can be exploited to execute denial of service attacks. The flaw specifically manifests when processing crafted ogg multimedia files, which are commonly used for audio and video streaming applications. FFmpeg, being a widely deployed multimedia framework used across numerous applications and platforms, makes this vulnerability particularly concerning for system administrators and security professionals.
The technical implementation of this vulnerability stems from improper memory allocation handling within the grow_array function. When FFmpeg processes an ogg file containing maliciously crafted data structures, the function fails to properly manage memory resources during array expansion operations. This memory leak occurs because allocated memory blocks are not correctly deallocated or recycled, leading to progressive memory consumption that eventually exhausts available system resources. The vulnerability operates at the core level of FFmpeg's command utility processing, making it difficult to detect and isolate through standard runtime monitoring mechanisms. According to CWE classification, this represents a CWE-401: Improper Release of Memory Before Removing Last Reference, which directly relates to memory management errors in software applications. The specific nature of the flaw allows attackers to repeatedly trigger the memory allocation path through carefully constructed ogg file payloads, amplifying the impact of each individual request.
The operational impact of CVE-2020-21690 extends beyond simple service disruption, creating potential cascading effects within systems that rely on FFmpeg for multimedia processing. Attackers can exploit this vulnerability by simply providing a maliciously crafted ogg file to any application that utilizes FFmpeg for media handling, including content management systems, media servers, and streaming platforms. The denial of service condition can be achieved with minimal computational resources, making it particularly dangerous in environments where resource constraints are already present. This vulnerability affects systems across multiple operating environments including Linux, Windows, and macOS, as FFmpeg is cross-platform. The attack vector is particularly insidious because ogg files are commonly used in web applications, making this vulnerability exploitable through web-based attack surfaces. From an ATT&CK framework perspective, this vulnerability maps to T1499.004: Endpoint Denial of Service, where the adversary leverages application-level flaws to consume system resources and render services unavailable.
Mitigation strategies for CVE-2020-21690 should prioritize immediate patching of affected FFmpeg installations to version 4.3 or later, where the memory leak has been corrected. System administrators should implement input validation and sanitization measures for all multimedia file processing pipelines, particularly those handling ogg format files. Network-level protections can include implementing file type filtering and content inspection mechanisms to prevent malicious ogg files from reaching vulnerable applications. Organizations should also consider deploying intrusion detection systems that can identify patterns associated with memory leak exploitation attempts. The fix implemented in newer FFmpeg versions addresses the root cause by ensuring proper memory deallocation in the grow_array function, preventing the accumulation of unreleased memory blocks. Additionally, application developers should review their FFmpeg integration code to ensure proper error handling and resource management practices are implemented. Regular security assessments and vulnerability scanning should be conducted to identify any potential exposure to similar memory management flaws within the broader multimedia processing stack.