Use After Free in Libpng
CVE-2026-34757
LIBPNG is a reference library for use in applications that read, create, and manipulate PNG (Portable Network Graphics) raster image files. From 1.0.9 to before 1.6.57, passing a pointer obtained from png_get_PLTE, png_get_tRNS, or png_get_hIST back into the corresponding setter on the same png_struct/png_info pair causes the setter to read from freed memory and copy its contents into the replacement buffer. The setter frees the internal buffer before copying from the caller-supplied pointer, which now dangles. The freed region may contain stale data (producing silently corrupted chunk metadata) or data from subsequent heap allocations (leaking unrelated heap contents into the chunk struct). This vulnerability is fixed in 1.6.57.
Vulnerability class: Use-After-Free
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.1 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.002 (4.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 5th percentile — 4.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: -0.000
Affected products
- Libpng
- Pnggroup Libpng — versions >= 1.0.9, < 1.6.57
- Debian Linux — versions 11.0
Weakness classification (CWE)
References
- github.com/pnggroup/libpng/security/advisories/GHSA-6fr7-g8h7-v645 (Patch, Mitigation, Vendor Advisory)
- github.com/pnggroup/libpng/issues/836 (Exploit, Mitigation, Issue Tracking)
- github.com/pnggroup/libpng/issues/837 (Exploit, Mitigation, Issue Tracking)
- github.com/pnggroup/libpng/commit/398cbe3df03f4e11bb031e07f416dfdde3684e8a (Patch)
- github.com/pnggroup/libpng/commit/55d20aaa322c9274491cda82c5cd4f99b48c6bcc (Patch)
- af854a3a-2127-422b-91ae-364da2661108 (Mailing List, Third Party Advisory)
Frequently asked questions
- What is CVE-2026-34757?
- CVE-2026-34757 is a medium-severity vulnerability in Libpng, classified under Use After Free. CVSS score: 5.1/10. Published 2026-04-09.
- How severe is CVE-2026-34757?
- Medium severity. CVSS v3 base score is 5.1 out of 10.