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.
History

Fri, 27 Mar 2026 12:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-124
References
Metrics threat_severity

None

threat_severity

Moderate


Fri, 27 Mar 2026 08:45:00 +0000

Type Values Removed Values Added
First Time appeared Pnggroup
Pnggroup libpng
Vendors & Products Pnggroup
Pnggroup libpng

Thu, 26 Mar 2026 19:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Thu, 26 Mar 2026 17:15:00 +0000

Type Values Removed Values Added
Description 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.
Title LIBPNG has ARM NEON Palette Expansion Out-of-Bounds Read on AArch64
Weaknesses CWE-125
CWE-787
References
Metrics cvssV3_1

{'score': 7.6, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published: 2026-03-26T16:51:58.289Z

Updated: 2026-03-26T18:45:26.631Z

Reserved: 2026-03-23T14:24:11.619Z

Link: CVE-2026-33636

cve-icon Vulnrichment

Updated: 2026-03-26T18:45:23.887Z

cve-icon NVD

Status : Received

Published: 2026-03-26T17:16:41.477

Modified: 2026-03-26T17:16:41.477

Link: CVE-2026-33636

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-03-26T16:51:58Z

Links: CVE-2026-33636 - Bugzilla