CVE-2016-6881 in FFmpeg
Summary
by MITRE
The zlib_refill function in libavformat/swfdec.c in FFmpeg before 3.1.3 allows remote attackers to cause an infinite loop denial of service via a crafted SWF file.
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Analysis
by VulDB Data Team • 10/12/2022
The vulnerability identified as CVE-2016-6881 represents a critical denial of service flaw within the FFmpeg multimedia framework, specifically affecting the zlib_refill function located in libavformat/swfdec.c. This issue enables remote attackers to trigger an infinite loop condition by crafting malicious SWF files that exploit the decompression logic within the software. The flaw manifests when FFmpeg processes specially constructed Shockwave Flash files, which can cause the application to enter an indefinite loop during the decompression phase, ultimately consuming excessive system resources and rendering the application unresponsive.
The technical root cause of this vulnerability stems from inadequate input validation and error handling within the SWF file parser's decompression routines. When the zlib_refill function processes compressed data from a malformed SWF file, it fails to properly validate the decompression parameters or detect abnormal decompression sequences that could lead to infinite iteration. This condition falls under the CWE-835 category of infinite loops and represents a classic example of improper handling of compressed data streams. The vulnerability demonstrates how compressed data processing can become a vector for resource exhaustion attacks, particularly when the decompression algorithm does not implement proper termination conditions or iteration limits.
From an operational perspective, this vulnerability poses significant risks to systems that process untrusted SWF content, including web servers, media processing platforms, and content delivery networks that handle user-uploaded Flash files. The infinite loop condition can be exploited by attackers to consume CPU cycles indefinitely, potentially leading to system resource exhaustion and service disruption. The impact extends beyond simple denial of service as it can affect the availability of multimedia processing services, potentially causing cascading failures in systems that rely on FFmpeg for video and audio processing tasks. This vulnerability specifically affects versions of FFmpeg prior to 3.1.3, making it a critical concern for organizations that have not yet updated their multimedia processing infrastructure.
Organizations affected by this vulnerability should prioritize immediate patching of their FFmpeg installations to version 3.1.3 or later, which contains the necessary fixes to prevent the infinite loop condition in the zlib_refill function. Additionally, implementing content validation measures such as strict file format checking, size limitations, and decompression timeout mechanisms can provide additional layers of protection. Security monitoring should include detection of unusual CPU usage patterns that might indicate exploitation attempts, and network-based intrusion detection systems should be configured to flag suspicious SWF file processing activities. The ATT&CK framework categorizes this vulnerability under the T1499.004 technique for network denial of service, highlighting the importance of proper input validation and resource management in multimedia processing applications to prevent exploitation through compressed data manipulation.