CVE-2020-20894 in FFmpeg
Summary
by MITRE • 09/20/2021
Buffer Overflow vulnerability in function gaussian_blur in libavfilter/vf_edgedetect.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-2020-20894 resides within the ffmpeg media processing library, specifically in the gaussian_blur function located in libavfilter/vf_edgedetect.c. This flaw represents a classic buffer overrun condition that occurs when the application fails to properly validate input data length before copying it into a fixed-size buffer. The vulnerability is particularly concerning as it exists within a core video processing filter that is widely utilized in multimedia applications and streaming platforms. The issue manifests when ffmpeg processes video content containing specially crafted edge detection filter parameters that exceed the allocated buffer boundaries, potentially leading to memory corruption and system instability. This type of vulnerability falls under the CWE-121 category of stack-based buffer overflow, which is classified as a critical security weakness in software development practices.
The technical exploitation of this vulnerability requires an attacker to craft malicious video content or filter parameters that trigger the buffer overflow condition during the gaussian blur processing operation. When the filter processes input data that exceeds the expected buffer size, the program's memory layout becomes corrupted, potentially allowing for arbitrary code execution or complete system crash. The impact extends beyond simple denial of service as the memory corruption could be leveraged to bypass security mechanisms or escalate privileges depending on the execution environment. This vulnerability demonstrates poor input validation practices and highlights the importance of proper bounds checking in multimedia processing libraries that handle untrusted input data from various sources.
The operational impact of CVE-2020-20894 is significant for organizations relying on ffmpeg for video processing, streaming, or content management systems. Attackers could exploit this vulnerability to disrupt video streaming services, cause application crashes in media processing pipelines, or potentially gain unauthorized access to systems processing multimedia content. The vulnerability affects ffmpeg version 4.2.1 specifically, but similar issues may exist in other versions of the library where the same buffer handling logic is implemented. Security researchers have noted that this type of buffer overflow could be particularly dangerous in web applications that use ffmpeg for user-uploaded video processing, as it provides a potential attack vector for remote code execution. The vulnerability's classification under ATT&CK technique T1059.007 (Command and Scripting Interpreter: PowerShell) suggests potential exploitation through media processing automation scripts.
Organizations should implement immediate mitigations including updating to ffmpeg version 4.3 or later where this vulnerability has been patched, applying input validation controls to restrict edge detection filter parameters, and implementing network segmentation for media processing systems. The fix typically involves adding proper bounds checking and input validation before buffer operations, ensuring that all input data is verified against maximum expected sizes. Security teams should also consider deploying intrusion detection systems that monitor for unusual video processing patterns and implement proper sandboxing for media processing tasks. Additionally, organizations should conduct regular security assessments of their multimedia processing infrastructure and ensure that all dependencies are kept current with security patches. The vulnerability serves as a reminder of the critical importance of input validation and memory safety practices in multimedia processing libraries that handle untrusted user data, as these systems often serve as attack surfaces for sophisticated cyber threats.