Vulnerability 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.
Related Weaknesses (CWE)
References
FAQ
What is CVE-2026-91186?
CVE-2026-91186 is a documented vulnerability. 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 ti...
How severe is CVE-2026-91186?
CVSS scoring is not yet available for CVE-2026-91186. Check NVD for updates.
Is there a patch for CVE-2026-91186?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.