CVE-2020-20896 in FFmpeg
Summary
by MITRE • 09/20/2021
An issue was discovered in function latm_write_packet in libavformat/latmenc.c in Ffmpeg 4.2.1, allows attackers to cause a Denial of Service or other unspecified impacts due to a Null pointer dereference.
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Analysis
by VulDB Data Team • 09/29/2021
The vulnerability identified as CVE-2020-20896 represents a critical null pointer dereference flaw within the FFmpeg multimedia framework's LATM (Low Overhead Audio Transport Multiplex) encoder implementation. This issue exists in the latm_write_packet function located in libavformat/latmenc.c file within FFmpeg version 4.2.1, making it particularly concerning given the widespread adoption of FFmpeg in media processing applications across various platforms and systems. The vulnerability arises from insufficient input validation and error handling mechanisms within the audio packet writing process, creating a potential attack vector that could be exploited by malicious actors to disrupt normal system operations.
The technical exploitation of this vulnerability occurs when an attacker crafts specially malformed LATM audio packets that trigger a null pointer dereference during the packet writing process. This flaw falls under CWE-476, which specifically addresses null pointer dereference conditions in software implementations. The function latm_write_packet fails to properly validate pointer references before attempting to access memory locations, allowing an attacker to manipulate the input data stream in such a way that a null pointer is dereferenced during normal packet processing operations. This type of vulnerability is particularly dangerous because it can be triggered through legitimate media file processing operations, making it difficult to detect and prevent through traditional network-based security measures.
The operational impact of CVE-2020-20896 extends beyond simple denial of service conditions, as the null pointer dereference can potentially lead to application crashes, system instability, and in some scenarios could be leveraged as a stepping stone for more sophisticated attacks. Systems utilizing FFmpeg for media processing, including streaming services, content management systems, and multimedia applications, could experience service interruptions when processing maliciously crafted audio files. The vulnerability affects the core encoding functionality of FFmpeg, meaning that any application relying on this library for LATM audio format processing could be compromised. This aligns with ATT&CK technique T1499.001, which describes denial of service attacks targeting application availability, and represents a significant concern for organizations that depend on FFmpeg for media handling operations.
Mitigation strategies for CVE-2020-20896 should prioritize immediate patching of affected FFmpeg installations to version 4.3 or later, where the null pointer dereference has been addressed through improved input validation and error handling mechanisms. Organizations should implement comprehensive input sanitization procedures for all media files processed through FFmpeg-based systems, including automatic format validation and content scanning before encoding operations. Network-based security controls such as intrusion detection systems and web application firewalls should be configured to monitor for suspicious media file patterns that could indicate exploitation attempts. Additionally, system administrators should consider implementing application sandboxing and privilege separation techniques to limit the potential impact of successful exploitation attempts, ensuring that even if an attacker successfully triggers the vulnerability, the damage remains contained within specific operational boundaries. Regular security assessments and vulnerability scanning should be conducted to identify any potential variants or related issues that may exist within the FFmpeg codebase or related multimedia processing components.