CVE-2026-66040 in FFmpeg
Summary
by MITRE • 07/24/2026
FFmpeg through 8.1.2, fixed in commit b506faf, contains a heap out-of-bounds write vulnerability in the native PNG and APNG encoders that allows remote attackers to corrupt heap memory by supplying a crafted PNG image with a malicious eXIf chunk. Attackers can craft an eXIf chunk where multiple IFD entries reference the same large value payload, causing canonical serialization to expand the output far beyond the undersized allocation estimated by add_exif_profile_size(), resulting in png_write_chunk() writing tens of thousands of bytes past the buffer boundary, leading to deterministic heap corruption, process crash, and potentially arbitrary code execution.
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Analysis
by VulDB Data Team • 07/26/2026
This vulnerability resides within the FFmpeg multimedia framework's handling of PNG and APNG image encoding processes, specifically affecting versions up through 8.1.2. The flaw manifests in the native PNG encoder's processing of eXIf chunks, which are extended image format chunks used to store EXIF metadata. When FFmpeg encounters a crafted PNG image containing an eXIf chunk with multiple IFD entries referencing identical large payload values, the canonical serialization process generates output that significantly exceeds the initially allocated buffer size. This occurs because the add_exif_profile_size() function underestimates the actual memory requirements needed for the serialized data, creating a heap buffer overflow condition.
The technical implementation of this vulnerability leverages the way FFmpeg calculates memory allocation for EXIF profile data during PNG encoding operations. The vulnerability stems from improper bounds checking and memory estimation within the PNG encoder's EXIF handling code path. When multiple IFD entries reference the same large payload, the canonical serialization process causes exponential expansion of the output buffer size beyond the allocated space determined by add_exif_profile_size(). This calculation error results in a heap out-of-bounds write condition where png_write_chunk() attempts to write tens of thousands of bytes past the originally allocated memory boundary. The vulnerability is classified as a heap-based buffer overflow with deterministic characteristics that can lead to reliable exploitation.
The operational impact of this vulnerability extends beyond simple memory corruption, creating potential for remote code execution in affected systems. When exploited, the heap corruption can cause process crashes or more critically enable attackers to achieve arbitrary code execution by carefully crafting the malicious eXIf chunk data. This makes the vulnerability particularly dangerous in server environments where FFmpeg processes untrusted user input, such as web applications handling image uploads or media processing services. The deterministic nature of the heap corruption means that attackers can reliably reproduce the exploit conditions, making this vulnerability suitable for automated attack scenarios.
Mitigation strategies should focus on immediate version updates to FFmpeg 8.1.3 or later where the vulnerability has been patched through commit b506faf. Organizations should implement input validation and sanitization measures for PNG image processing workflows, particularly when handling untrusted inputs from external sources. The fix addresses the core issue by improving the memory estimation algorithm in add_exif_profile_size() to properly account for canonical serialization expansion factors. Security practitioners should also consider implementing network-level protections such as content filtering and sandboxing mechanisms around FFmpeg processes to reduce the attack surface. This vulnerability aligns with CWE-787 (Out-of-bounds Write) and can be mapped to ATT&CK technique T1059.007 (Command and Scripting Interpreter: Python) through potential exploitation vectors involving media processing applications that may execute malicious payloads during image handling operations.
The vulnerability demonstrates the critical importance of proper memory management in multimedia processing libraries, where buffer overflows can occur during complex serialization processes. FFmpeg's extensive use across various platforms and applications means that successful exploitation could affect numerous downstream systems including web servers, content management systems, and media processing pipelines. Organizations should conduct thorough security assessments of their FFmpeg usage patterns and implement comprehensive monitoring for potential exploitation attempts. The patch resolution specifically addresses the root cause by modifying the buffer size calculation logic to prevent under-allocation during EXIF profile serialization, thereby eliminating the conditions that lead to the heap corruption scenario.