CVE-2018-7751 in FFmpeg
Summary
by MITRE
The svg_probe function in libavformat/img2dec.c in FFmpeg through 3.4.2 allows remote attackers to cause a denial of service (Infinite Loop) via a crafted XML file.
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Analysis
by VulDB Data Team • 03/07/2023
The vulnerability identified as CVE-2018-7751 represents a critical denial of service flaw within the FFmpeg multimedia framework that affects versions through 3.4.2. This issue resides in the svg_probe function located within the libavformat/img2dec.c source file, which is responsible for detecting and processing image format files including scalable vector graphics. The vulnerability manifests when FFmpeg encounters a specially crafted XML file that triggers an infinite loop during the format detection phase, effectively consuming system resources and rendering the application unresponsive.
The technical implementation of this vulnerability exploits a flaw in the format probing mechanism where the svg_probe function fails to properly validate XML structure and content during the initial detection process. When processing maliciously constructed XML data, the function enters a condition where it repeatedly iterates through a loop without proper termination conditions, causing the application to hang indefinitely. This behavior constitutes a classic infinite loop vulnerability that falls under CWE-835, which specifically addresses the issue of loops without proper exit conditions. The flaw demonstrates how improper input validation can lead to resource exhaustion and system instability.
From an operational perspective, this vulnerability presents significant risks to systems that rely on FFmpeg for multimedia processing, particularly in environments where untrusted input is processed such as content management systems, media servers, or web applications. Attackers can exploit this vulnerability by uploading or transmitting a crafted XML file that appears legitimate but contains malformed structures designed to trigger the infinite loop. The impact extends beyond simple service disruption as the infinite loop can consume CPU resources and memory, potentially leading to system crashes or denial of service for legitimate users. This vulnerability aligns with ATT&CK technique T1499.001 which covers network denial of service attacks, and represents a critical weakness in the input validation and resource management controls of multimedia processing frameworks.
The mitigation strategy for CVE-2018-7751 requires immediate patching of FFmpeg installations to versions 3.4.3 or later where the vulnerability has been addressed through proper loop termination conditions and enhanced input validation. Organizations should also implement additional defensive measures including input sanitization, rate limiting, and resource monitoring to detect and prevent exploitation attempts. Network administrators should consider implementing intrusion detection systems that can identify patterns associated with this specific vulnerability and block suspicious XML content. The fix implemented in the patched versions addresses the root cause by introducing proper boundary checks and termination conditions within the svg_probe function, preventing the infinite loop condition from occurring while maintaining legitimate functionality for valid SVG files.