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CVE-2026-33416— LIBPNG has use-after-free via pointer aliasing in `png_set_tRNS` and `png_set_PLTE`

Quick assessment

Affected
pnggroup libpng
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

libpng是The PNG Development Group开源的一个可对PNG图形文件实现创建、读写等操作的PNG参考库。 LIBPNG 1.6.55及之前版本存在资源管理错误漏洞，该漏洞源于png_set_tRNS和png_set_PLTE函数存在别名和悬垂指针，可能导致释放后重用。

CVSS 7.5 · High EPSS 1.07% · P65

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-33416

Vulnerability Information
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Vulnerability Title
LIBPNG has use-after-free via pointer aliasing in `png_set_tRNS` and `png_set_PLTE`
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
释放后使用
Source: CVE Program / CVE List V5
Vulnerability Title
libpng 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
libpng是The PNG Development Group开源的一个可对PNG图形文件实现创建、读写等操作的PNG参考库。 LIBPNG 1.6.55及之前版本存在资源管理错误漏洞，该漏洞源于png_set_tRNS和png_set_PLTE函数存在别名和悬垂指针，可能导致释放后重用。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
pnggroup libpng >= 1.2.1, < 1.6.56 -

II. Public POCs for CVE-2026-33416

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III. Intelligence Information for CVE-2026-33416

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Patches & Fixes for CVE-2026-33416 (5)

Vendor Advisories for CVE-2026-33416 (1)

IV. Related Vulnerabilities

Same product: libpng
Same vendor: pnggroup
Same weakness: CWE-416