CVE-2026-91186 PNG decoder: a duplicate IHDR chunk after IDAT resizes the image after allocation, causing a heap out-of-bounds write
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-91186?
CVE-2026-91186 is a high-severity vulnerability in Eclipse ThreadX - GUIX, published on 20 Oct 2026.
Official description
The PNG chunk reader has no notion of chunk ordering. It records whether an IDAT has been seen and whether a tRNS has already supplied transparency, but nothing prevents an IHDR being read a second time.
A PNG carries exactly one IHDR and it is the first chunk. A file that places a second one after IDAT rewrites the image width, height, bit depth and pixel depth *after* the decoded-data buffer has already been allocated and filled from the original values. The pass that reverses the PNG row filters then derives its own extent from the new dimensions and walks the old allocation, moving image bytes past the end of it.
The buffer is allocated by GUIX rather than supplied by the caller, so the application has no way to size it defensively. The decoder is compiled in by default.
Which versions are affected by CVE-2026-91186?
How do I fix CVE-2026-91186?
No fix has been published for CVE-2026-91186 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-91186 being exploited?
There is no known exploitation of CVE-2026-91186 in the wild and no public exploit code.
Sources
Also known as GHSA-gx8f-4rpc-4fjw.