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VulnerabilityPublished Updated

CVE-2026-33416: pnggroup libpng · Use After Free

Affects pnggroup libpngSource CVE Database V5

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Not known to be exploited · CVSS 7.5 High : upgrade to 1.6.56 soon.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score
7.5High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
1.0% chance of exploitation in 30 days – higher than 64% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 1.6.56
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 26 Mar 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

What to do

Upgrade libpng and pnggroup/libpng to 1.6.56.

Affected software

ProductAffectedFixed in
pnggrouplibpngAffected
  • >=1.2.1 <1.6.56
Fixed in
  • 1.6.56
GitHubpnggroup/libpngpkg:github/pnggroup/libpngOther threatsAffected
  • <1.6.56
Fixed in
  • 1.6.56

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix is available in libpng version 1.6.56. Users and developers should upgrade to version 1.6.56 or later to remediate this vulnerability. No vendor advisory was provided in the input, but the version information clearly indicates the fixed release. Until upgrading, avoid processing untrusted PNG files with affected versions to reduce risk.

Description

LIBPNG is a reference library for use in applications that read, create, and manipulate PNG (Portable Network Graphics) raster image files. In versions 1.2.1 through 1.6.55, `png_set_tRNS` and `png_set_PLTE` each alias a heap-allocated buffer between `png_struct` and `png_info`, sharing a single allocation across two structs with independent lifetimes. The `trans_alpha` aliasing has been present since at least libpng 1.0, and the `palette` aliasing since at least 1.2.1. Both affect all prior release lines `png_set_tRNS` sets `png_ptr->trans_alpha = info_ptr->trans_alpha` (256-byte buffer) and `png_set_PLTE` sets `info_ptr->palette = png_ptr->palette` (768-byte buffer). In both cases, calling `png_free_data` (with `PNG_FREE_TRNS` or `PNG_FREE_PLTE`) frees the buffer through `info_ptr` while the corresponding `png_ptr` pointer remains dangling. Subsequent row-transform functions dereference and, in some code paths, write to the freed memory. A second call to `png_set_tRNS` or `png_set_PLTE` has the same effect, because both functions call `png_free_data` internally before reallocating the `info_ptr` buffer. Version 1.6.56 fixes the issue.

References

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