CVE-2020-20892 in FFmpeg
Summary
by MITRE • 09/20/2021
An issue was discovered in function filter_frame in libavfilter/vf_lenscorrection.c in Ffmpeg 4.2.1, allows attackers to cause a Denial of Service or other unspecified impacts due to a division by zero.
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Analysis
by VulDB Data Team • 09/29/2021
The vulnerability identified as CVE-2020-20892 represents a critical denial of service weakness within the FFmpeg multimedia framework version 4.2.1. This issue resides in the filter_frame function located within the libavfilter/vf_lenscorrection.c module, which handles lens correction filtering operations for video processing. The flaw manifests when the software encounters specific input parameters that trigger a division by zero error during the lens correction algorithm execution. This particular vulnerability falls under the CWE-369 category of Divide by Zero, which is classified as a common weakness in software security practices. The affected component specifically processes video frames through lens correction filters, making it a potential target for attackers seeking to disrupt multimedia processing services.
The technical implementation of this vulnerability occurs when the filter_frame function attempts to perform mathematical operations on input parameters that result in a zero denominator during calculations. The lens correction filter processes video data to compensate for optical distortions introduced by camera lenses, requiring precise mathematical computations involving ratios and geometric transformations. When malformed or specially crafted input data is processed through this filter, the algorithm fails to properly validate denominator values, leading to the division by zero condition. This error causes the application to terminate abruptly or enter an unstable state, effectively rendering the multimedia processing service unavailable to legitimate users. The vulnerability is particularly concerning as it can be triggered through normal video processing workflows without requiring special privileges or complex attack vectors.
From an operational perspective, this vulnerability poses significant risks to systems that rely on FFmpeg for video processing tasks, including content delivery networks, media servers, and streaming platforms. Attackers can exploit this weakness by providing malicious video files or manipulating input parameters to trigger the division by zero condition, resulting in service disruption and potential denial of service for legitimate users. The impact extends beyond simple service interruption as the vulnerability can potentially be leveraged in more sophisticated attack scenarios where multiple service disruptions could be orchestrated. The ATT&CK framework categorizes this type of vulnerability under the T1499.004 technique of Network Denial of Service, making it a valuable target for attackers seeking to compromise system availability. Organizations using FFmpeg in production environments face potential business disruption and reputation damage if this vulnerability is exploited.
The recommended mitigation strategy involves upgrading to FFmpeg version 4.3 or later, where the division by zero issue has been resolved through proper input validation and error handling mechanisms. System administrators should prioritize patching affected installations and implementing monitoring protocols to detect potential exploitation attempts. Additionally, input validation should be enhanced at the application level to prevent malformed data from reaching the vulnerable filter functions. Security teams should consider implementing network segmentation and access controls to limit exposure of FFmpeg-based services to untrusted inputs. The vulnerability highlights the importance of thorough input validation in multimedia processing libraries and demonstrates how seemingly minor mathematical errors can lead to significant security implications. Organizations should also conduct regular security assessments of their multimedia processing pipelines to identify and remediate similar weaknesses before they can be exploited by malicious actors.