LIBPNG has ARM NEON Palette Expansion Out-of-Bounds Read on AArch64

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.

Problem type

Affected products

pnggroup

libpng

>= 1.6.36, < 1.6.56 - AFFECTED

References

https://github.com/pnggroup/libpng/security/advisories/GHSA-wjr5-c57x-95m2

https://github.com/pnggroup/libpng/security/advisories/GHSA-wjr5-c57x-95m2

x_refsource_CONFIRM

https://github.com/pnggroup/libpng/commit/7734cda20cf1236aef60f3bbd2267c97bbb40869

https://github.com/pnggroup/libpng/commit/7734cda20cf1236aef60f3bbd2267c97bbb40869

x_refsource_MISC

https://github.com/pnggroup/libpng/commit/aba9f18eba870d14fb52c5ba5d73451349e339c3

https://github.com/pnggroup/libpng/commit/aba9f18eba870d14fb52c5ba5d73451349e339c3

x_refsource_MISC

JSON source

https://cveawg.mitre.org/api/cve/CVE-2026-33636

Click to expand

{
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  "dataVersion": "5.2",
  "cveMetadata": {
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    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "dateUpdated": "2026-03-26T18:45:26.631Z",
    "dateReserved": "2026-03-23T14:24:11.619Z",
    "datePublished": "2026-03-26T16:51:58.289Z",
    "state": "PUBLISHED"
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      },
      "title": "LIBPNG has ARM NEON Palette Expansion Out-of-Bounds Read on AArch64",
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          "value": "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."
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            "attackComplexity": "LOW",
            "privilegesRequired": "NONE",
            "userInteraction": "REQUIRED",
            "scope": "UNCHANGED",
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