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Use After FreeWeakness · CWE-416

CVE-2025-59734

HIGH · 8.7 CVSS v4.0 Published 2025-10-06
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
90/100
Remediation priority · Urgent
No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
It is possible to cause an use-after-free write in SANM decoding with a carefully crafted animation using subversion <2. When a STOR chunk is present, a subsequent FOBJ chunk will be saved in ctx->stored_frame. Stored frames can later be referenced by FTCH chunks. For files using subversion < 2, the undecoded frame is stored, and decoded again when the FTCH chunks are parsed. However, in process_frame_obj if the frame has an invalid size, there’s an early return, with a value of 0.  This causes the code in decode_frame to still store the raw frame buffer into ctx->stored_frame. Leaving ctx->has_dimensions set to false. A subsequent chunk with type FTCH would call process_ftch and decode that frame obj again, adding to the top/left values and calling process_frame_obj again. Given that we never set ctx->have_dimensions before, this time we set the dimensions, calling init_buffers, which can reallocate the buffer in ctx->stored_frame, freeing the previous one. However, the GetByteContext object gb still holds a reference to the old buffer. Finally, when the code tries to decode the frame, codecs that accept a GetByteContext as a parameter will trigger a use-after-free read when using gb. GetByteContext is only used for reading bytes, so at most one could read invalid data. There are no heap allocations between the free and when the object is accessed. However, upon returning to process_ftch, the code restores the original values for top/left in stored_frame, writing 4 bytes to the freed data at offset 6, potentially corrupting the allocator’s metadata. This issue can be triggered just by probing whether a file has the sanm format. We recommend upgrading to version 8.0 or beyond.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A use-after-free vulnerability exists in the SANM animation decoder where an early return in process_frame_obj when handling invalid frame sizes leaves ctx->has_dimensions false. When a subsequent FTCH chunk processes the stored frame, init_buffers reallocates the buffer while a GetByteContext still references the old freed memory, leading to use-after-free read and write operations that can corrupt heap metadata.

MitigationUpgrade to libavformat version 8.0 or later to obtain the patch that properly handles the frame dimension state and buffer lifecycle.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Adjacent
Complexity
High
Privileges
None
Authentication
X
User interaction
P
Scope
X

CVSS:4.0/AV:A/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify if SANM animation decoder is in use
    Search for libavformat or ffmpeg libraries in your environment, and check if your application processes .sanm or SANM animation files
    Affected if The system processes SANM animation files using libavformat versions prior to 8.0
  2. Determine libavformat version
    Run 'ffmpeg -version' or check the shared library version (e.g., libavformat.so) to obtain the installed version number
    Affected if The installed version is lower than 8.0 (the patched version)
  3. Verify SANM decoder is compiled/enabled
    Run 'ffmpeg -decoders 2>/dev/null | grep -i sanm' or check ffmpeg -codecs to confirm the SANM decoder is available in the build
    Affected if The SANM decoder is present and enabled in the build
  4. Check for SANM file processing paths
    Review application logs, file type handling code, or network traffic logs for processing of .sanm extension files or 'FTCH' chunk signatures
    Affected if The environment processes SANM animation files, which triggers the vulnerable code path

A system is affected if it uses libavformat version below 8.0 and processes SANM animation files that can trigger the vulnerable buffer reallocation in the SANM decoder.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to libavformat version 8.0 or later to obtain the patch that properly handles the frame dimension state and buffer lifecycle.

Have this fixed Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
16.0 hours of engineering $2,760
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-59734 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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