CVE-2021-38094 in FFmpeg
Summary
by MITRE • 09/20/2021
Integer Overflow vulnerability in function filter_sobel 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 • 08/30/2025
The integer overflow vulnerability identified as CVE-2021-38094 resides within the FFmpeg multimedia framework's libavfilter component, specifically in the filter_sobel function located in the vf_convolution.c file. This flaw affects FFmpeg version 4.2.1 and represents a critical security concern that can be exploited by malicious actors to disrupt system operations. The vulnerability manifests when the function processes image convolution operations, particularly those involving Sobel edge detection filters that are commonly used in video processing pipelines. The integer overflow occurs during the calculation of buffer sizes or loop counters, where maliciously crafted input parameters can cause arithmetic operations to exceed the maximum representable value for signed integers.
The technical implementation of this vulnerability stems from insufficient input validation and boundary checking within the filter_sobel function. When processing video frames through the convolution filter, the function performs mathematical operations that assume certain parameters will remain within expected ranges. However, an attacker can manipulate input values to cause integer overflow conditions that result in unexpected memory allocation behaviors. This flaw operates under CWE-190, which classifies integer overflow conditions as a fundamental weakness in software design. The vulnerability can be triggered through various attack vectors including malformed video files, crafted image sequences, or manipulated filter parameters that are passed to the affected function. The specific nature of the integer overflow creates a scenario where legitimate operations become corrupted, potentially leading to buffer overflows, memory corruption, or unexpected program termination.
The operational impact of CVE-2021-38094 extends beyond simple denial of service conditions, as it can potentially enable more sophisticated attack scenarios. Systems utilizing FFmpeg for video processing, content management, or media transcoding are at risk when they process untrusted input data. The vulnerability can be exploited in environments where FFmpeg serves as a backend component for web applications, media servers, or content delivery networks. Attackers may leverage this flaw to cause service disruption by forcing application crashes or system hangs, which can result in significant downtime and operational losses. Additionally, the vulnerability may create opportunities for information disclosure or privilege escalation in certain configurations where FFmpeg operates with elevated permissions. The impact is particularly concerning in cloud environments or multi-tenant systems where resource exhaustion could affect other services running on the same infrastructure, aligning with ATT&CK technique T1499.1 for resource hijacking and system disruption.
Mitigation strategies for CVE-2021-38094 should prioritize immediate patching of affected FFmpeg installations to version 4.4 or later, where the integer overflow has been addressed through proper input validation and boundary checking mechanisms. Organizations should implement comprehensive input sanitization protocols for all media processing workflows, particularly those involving untrusted user uploads or third-party content. Network segmentation and access controls should be enforced to limit exposure of FFmpeg-based services to potentially malicious inputs. Security monitoring should include detection of unusual resource consumption patterns or process termination events that may indicate exploitation attempts. Regular vulnerability assessments and penetration testing should be conducted to identify similar integer overflow conditions within other multimedia processing libraries and components. The fix implemented by FFmpeg developers addresses the core mathematical operations in the filter_sobel function by introducing proper bounds checking and overflow detection mechanisms that prevent malicious inputs from causing arithmetic overflows. System administrators should also consider implementing automated patch management processes to ensure rapid deployment of security updates across all affected systems and applications that depend on FFmpeg for multimedia processing capabilities.