CVE-2020-20898 in FFmpeg
Summary
by MITRE • 09/20/2021
Integer Overflow vulnerability in function filter16_prewitt in libavfilter/vf_convolution.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 CVE-2020-20898 vulnerability represents a critical integer overflow flaw within the FFmpeg multimedia framework's libavfilter component, specifically in the filter16_prewitt function located in vf_convolution.c. This vulnerability arises from improper input validation and arithmetic handling when processing convolution operations, particularly affecting the prewitt edge detection filter. The flaw manifests when the application processes malformed input data that triggers integer overflow conditions during calculation of filter parameters. The vulnerability is classified under CWE-190 as an integer overflow error, which occurs when a program performs arithmetic operations on signed integers without proper bounds checking, leading to unexpected behavior when the result exceeds the maximum value that can be represented by the data type. This particular implementation within FFmpeg's video processing pipeline exposes the system to potential exploitation through crafted media files that trigger the overflow condition during filter application.
The technical exploitation of this vulnerability occurs when an attacker submits specially crafted video content that forces the filter16_prewitt function to perform calculations resulting in integer overflow. The overflow can occur during the computation of filter dimensions or coefficients, where the mathematical operations exceed the capacity of the integer variables used to store intermediate results. When this happens, the program may allocate insufficient memory, cause buffer overflows, or trigger unexpected program behavior that can lead to application crashes. The vulnerability is particularly dangerous because it can be triggered through normal media processing workflows, meaning that any application using FFmpeg's libavfilter component could be affected when processing untrusted input. This makes the impact widespread across various software systems that rely on FFmpeg for video processing, including media servers, content management systems, and streaming platforms.
The operational impact of CVE-2020-20898 extends beyond simple denial of service, as it can potentially enable more sophisticated attacks depending on the execution context. While the primary effect is a denial of service through application crashes, the integer overflow could theoretically be leveraged to cause memory corruption or information disclosure if the overflowed values are used in subsequent operations without proper validation. Attackers could potentially craft media files that, when processed by vulnerable systems, cause the application to crash repeatedly, effectively creating a persistent denial of service condition. The vulnerability's exploitation is relatively straightforward, requiring only the creation of a malformed video file that triggers the specific filter path. This makes it particularly attractive to threat actors seeking to disrupt services, as the attack vector is accessible through standard media file handling channels without requiring advanced exploitation techniques or specialized knowledge of the underlying system architecture. The vulnerability's presence in FFmpeg 4.2.1 indicates a persistent issue that affects numerous downstream applications, making it a significant concern for system administrators and security professionals.
Mitigation strategies for CVE-2020-20898 should focus on immediate patching of affected FFmpeg installations to the latest stable versions that contain the fix for this integer overflow condition. System administrators should implement input validation and sanitization measures for all media processing workflows, particularly when handling untrusted content from external sources. The implementation of proper bounds checking and integer overflow detection mechanisms within the application code can help prevent exploitation of similar vulnerabilities in other components. Organizations should also consider implementing network-level protections such as content inspection and filtering to prevent malicious media files from reaching systems that process video content. Additionally, regular security audits of multimedia processing pipelines and dependency updates can help identify and remediate similar vulnerabilities before they can be exploited. The ATT&CK framework categorizes this vulnerability under T1499.004 as a denial of service attack, emphasizing the importance of protecting against resource exhaustion and application stability issues. Organizations should also monitor for related vulnerabilities in the same codebase and ensure that their security monitoring systems can detect anomalous behavior patterns that may indicate exploitation attempts.