FFmpeg through 9.0.2 Heap Overflow via Nellymoser Encoder Trellis Search
- Exploited
- No known exploitation
- Fix
- Fix or patch referenced
- Who is exposed
- Specific setups only
Do first: Check whether your setup matches what the bug needs. Applications encoding Nellymoser audio with trellis enabled Affects FFmpeg versions up to and including 9.0.2
- Last modified
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 12/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
FFmpeg through version 9.0.2 has a heap overflow in its Nellymoser audio encoder that can be triggered by an attacker supplying crafted audio to an application that encodes Nellymoser with trellis enabled. Exploiting it requires local access and some user action, and a successful attack could overwrite adjacent heap memory.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
FFmpeg through 9.0.2 contains an off-by-one heap overflow vulnerability in get_exponent_dynamic() in libavcodec/nellymoserenc.c that allows writing one element past the opt and path allocations. Attackers can supply crafted audio to applications encoding Nellymoser with trellis enabled, causing idx to equal OPT_SIZE and overwrite adjacent heap memory.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure5/25Specific setups only
- Reach?/20Unknown. No tracked technology or package matched
- Severity7.3/10CVSS 7.3
- No patch0/5No signal
What would change the score
- Would score about 62 if added to CISA KEV
- Would score about 57 if CISA's SSVC rates exploitation active
- Would score about 22 if CISA's SSVC rates it automatable
What to do
Check whether your setup matches what the bug needs.
Applications encoding Nellymoser audio with trellis enabled Affects FFmpeg versions up to and including 9.0.2Apply the patch listed under Evidence.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- FFmpeg FFmpeg
through 9.0.2
Evidence 5
- Patch
- Report
- Repository
- Repository
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-125257
Is CVE-2026-125257 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
The Nellymoser audio encoder's trellis search writes one element past the end of its opt and path buffers. This overwrites adjacent heap memory, which is a heap overflow.Source: vulncheck.com
Which versions are affected by CVE-2026-125257?
FFmpeg: through 9.0.2.Source: cve.now feed data
Am I affected, and how do I check?
FFmpeg versions up to and including 9.0.2 are affected, but only when Nellymoser audio is encoded with trellis enabled. To check, look at the FFmpeg version reported by ffmpeg -version and whether the encode command or application settings enable trellis for the Nellymoser encoder.Source: vulncheck.com
How do I fix CVE-2026-125257?
No fixed release is listed in the checked facts, so no specific upgrade target can be named. Check the FFmpeg project or your distribution for a patched build newer than 9.0.2.Source: vulncheck.com