Out-of-bounds Read in Libpng
CVE-2026-33636
LIBPNG is a reference library for use in applications that read, create, and manipulate PNG (Portable Network Graphics) raster image files. In versions 1.6.36 through 1.6.55, an out-of-bounds read and write exists in libpng's ARM/AArch64 Neon-optimized palette expansion path. When expanding 8-bit paletted rows to RGB or RGBA, the Neon loop processes a final partial chunk without verifying that enough input pixels remain. Because the implementation works backward from the end of the row, the final iteration dereferences pointers before the start of the row buffer (OOB read) and writes expanded pixel data to the same underflowed positions (OOB write). This is reachable via normal decoding of attacker-controlled PNG input if Neon is enabled. Version 1.6.56 fixes the issue.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.6 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H.
EPSS exploit prediction
EPSS: 0.004 (27.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 28th percentile — 27.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.007 · newest: 0.004 · change: -0.004
Affected products
- Libpng
- Pnggroup Libpng — versions >= 1.6.36, < 1.6.56
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-33636?
- CVE-2026-33636 is a high-severity vulnerability in Libpng, classified under Out-of-bounds Read. CVSS score: 7.6/10. Published 2026-03-26.
- How severe is CVE-2026-33636?
- High severity. CVSS v3 base score is 7.6 out of 10.