CVE-2025-59729 in FFmpeg
Summary
by MITRE • 10/06/2025
When parsing the header for a DHAV file, there's an integer underflow in offset calculation that leads to reading the duration from before the start of the allocated buffer.
If we load a DHAV file that is larger than MAX_DURATION_BUFFER_SIZE bytes (0x100000) for example 0x101000 bytes, then at [0] we have size = 0x101000. At [1] we have end_buffer_size = 0x100000, and at [2] we have end_buffer_pos = 0x1000.
The loop then scans backwards through the buffer looking for the dhav tag; when it is found, we'll calculate end_pos based on a 32-bit offset read from the buffer.
There is subsequently a check [3] that end_pos is within the section of the file that has been copied into end_buffer, but it only correctly handles the cases where end_pos is before the start of the file or after the section copied into end_buffer, and not the case where end_pos is within the the file, but before the section copied into end_buffer. If we provide such an offset, (end_pos - end_buffer_pos) can underflow, resulting in the subsequent access at [4] occurring before the beginning of the allocation.
We recommend upgrading to version 8.0 or beyond.
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Analysis
by VulDB Data Team • 06/21/2026
The vulnerability described in CVE-2025-59729 represents a critical integer underflow condition within the DHAV file parser that can lead to arbitrary code execution through buffer corruption. This flaw exists in the offset calculation logic when processing large DHAV files that exceed the maximum duration buffer size of 0x100000 bytes. The vulnerability manifests when a file larger than the allocated buffer is processed, creating a scenario where the parser attempts to calculate positions within the file that fall outside the bounds of the allocated memory region. The underlying issue stems from a fundamental miscalculation in how the parser handles the relationship between file offsets and buffer boundaries during header parsing operations.
The technical implementation of this vulnerability involves a complex interplay between buffer management and offset arithmetic within the parser's loop structure. When processing a DHAV file of 0x101000 bytes, the parser correctly identifies that the file exceeds the allocated buffer size of 0x100000 bytes and sets end_buffer_size to 0x100000 and end_buffer_pos to 0x1000. The parser then scans backwards through the buffer to locate the dhav tag, and upon finding it, reads a 32-bit offset value that determines end_pos. The vulnerability occurs because the validation check only accounts for two scenarios - when end_pos is either before the start of the file or after the end of the copied section - but fails to properly handle cases where end_pos falls within the file boundaries but before the section that was copied into end_buffer. This oversight creates a condition where the arithmetic operation (end_pos - end_buffer_pos) can underflow, resulting in a negative value that translates to an invalid memory access.
The operational impact of this vulnerability extends beyond simple buffer over-read conditions and can enable sophisticated attack vectors including memory corruption and potential code execution. The integer underflow creates a situation where memory access occurs at an offset that is calculated to be negative, effectively causing the parser to read from memory locations before the beginning of the allocated buffer. This type of vulnerability aligns with CWE-191, which specifically addresses integer underflows, and represents a classic example of how improper boundary checking can lead to memory safety violations. From an attacker's perspective, this vulnerability could be exploited to manipulate program flow by corrupting adjacent memory regions, potentially leading to privilege escalation or denial of service conditions. The ATT&CK framework categorizes this as a memory corruption technique under the T1059.007 sub-technique for execution through memory manipulation.
The recommended mitigation strategy involves upgrading to version 8.0 or later, which includes proper bounds checking and integer overflow protection mechanisms. This upgrade addresses the core issue by implementing robust validation of offset calculations and ensuring that all arithmetic operations maintain proper boundary constraints. Additional defensive measures should include implementing input validation for file size parameters, establishing proper buffer size limits, and deploying runtime protections such as address space layout randomization and stack canaries. Organizations should also consider implementing automated scanning tools to identify systems running vulnerable versions and establish monitoring protocols to detect potential exploitation attempts. The vulnerability demonstrates the importance of comprehensive testing for edge cases in buffer management and offset calculations, particularly in multimedia file parsers where complex binary formats are processed.