CVE-2017-7866 in FFmpeg
Summary
by MITRE
FFmpeg before 2017-01-23 has an out-of-bounds write caused by a stack-based buffer overflow related to the decode_zbuf function in libavcodec/pngdec.c.
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Analysis
by VulDB Data Team • 11/29/2022
The vulnerability identified as CVE-2017-7866 represents a critical stack-based buffer overflow in the FFmpeg multimedia framework that was disclosed in early 2017. This flaw exists within the decode_zbuf function located in the libavcodec/pngdec.c file, which is responsible for decoding PNG (Portable Network Graphics) image files. The issue arises when FFmpeg processes specially crafted PNG files that contain malformed zbuf (zlib compressed buffer) data, creating conditions where the application writes beyond the bounds of allocated stack memory. Such out-of-bounds write vulnerabilities are particularly dangerous because they can lead to arbitrary code execution when exploited by malicious actors who craft specific input files designed to trigger the overflow condition.
The technical implementation of this vulnerability stems from inadequate bounds checking within the PNG decompression routine. When FFmpeg encounters a PNG file with malformed zbuf data, the decode_zbuf function fails to properly validate the size of data being written to stack buffers, allowing attackers to overwrite adjacent memory locations. This memory corruption can potentially overwrite return addresses, function pointers, or other critical program state information, providing attackers with opportunities to redirect program execution flow. The vulnerability specifically affects versions of FFmpeg released prior to January 23, 2017, indicating that the fix was implemented in response to this particular flaw. The root cause aligns with CWE-121, which describes stack-based buffer overflow conditions where insufficient bounds checking allows data to be written beyond the boundaries of stack-allocated buffers.
The operational impact of CVE-2017-7866 extends across numerous applications and systems that rely on FFmpeg for multimedia processing, including media players, content management systems, web applications, and digital asset management platforms. Attackers can exploit this vulnerability by delivering malicious PNG files through various attack vectors such as email attachments, web downloads, or file sharing platforms, making it particularly dangerous in environments where users may encounter untrusted multimedia content. The vulnerability's exploitation potential aligns with ATT&CK technique T1203, which covers exploitation of software vulnerabilities, and T1059, covering command and scripting interpreter usage, as successful exploitation could enable attackers to execute arbitrary code on affected systems. Organizations using FFmpeg-based applications are at risk of complete system compromise, data theft, or denial of service conditions when this vulnerability is successfully exploited.
Mitigation strategies for CVE-2017-7866 primarily focus on immediate version updates to FFmpeg releases that contain the necessary patches addressing the stack buffer overflow. System administrators should prioritize upgrading to FFmpeg versions released after January 23, 2017, which include fixes specifically targeting the decode_zbuf function in pngdec.c. Additionally, implementing input validation measures such as PNG file format verification, size limitations on uploaded files, and sandboxed processing environments can help reduce the attack surface. Organizations should also consider deploying network-based intrusion detection systems that can identify suspicious PNG file patterns and implement strict content filtering policies for multimedia files. The vulnerability demonstrates the importance of maintaining up-to-date multimedia libraries and frameworks, as it represents a classic example of how seemingly benign file format processing can become a critical security risk when proper bounds checking is absent from the implementation.