CVE-2026-33416 (GCVE-0-2026-33416)
Vulnerability from cvelistv5 – Published: 2026-03-26 16:48 – Updated: 2026-04-01 03:55
VLAI?
Title
LIBPNG has use-after-free via pointer aliasing in `png_set_tRNS` and `png_set_PLTE`
Summary
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.
Severity ?
7.5 (High)
CWE
- CWE-416 - Use After Free
Assigner
References
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"id": "CVE-2026-33416",
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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 1.2.1 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-\u003etrans_alpha = info_ptr-\u003etrans_alpha` (256-byte buffer) and `png_set_PLTE` sets `info_ptr-\u003epalette = png_ptr-\u003epalette` (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."
}
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"title": "LIBPNG has use-after-free via pointer aliasing in `png_set_tRNS` and `png_set_PLTE`"
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"nvd": "{\"cve\":{\"id\":\"CVE-2026-33416\",\"sourceIdentifier\":\"security-advisories@github.com\",\"published\":\"2026-03-26T17:16:38.443\",\"lastModified\":\"2026-04-02T20:28:33.973\",\"vulnStatus\":\"Analyzed\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"LIBPNG is a reference library for use in applications that read, create, and manipulate PNG (Portable Network Graphics) raster image files. In versions 1.2.1 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-\u003etrans_alpha = info_ptr-\u003etrans_alpha` (256-byte buffer) and `png_set_PLTE` sets `info_ptr-\u003epalette = png_ptr-\u003epalette` (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.\"},{\"lang\":\"es\",\"value\":\"LIBPNG es una biblioteca de referencia para su uso en aplicaciones que leen, crean y manipulan archivos de imagen r\u00e1ster PNG (Portable Network Graphics). En las versiones 1.2.1 a 1.6.55, \u0027png_set_tRNS\u0027 y \u0027png_set_PLTE\u0027 cada una aliasan un b\u00fafer asignado en el heap entre \u0027png_struct\u0027 y \u0027png_info\u0027, compartiendo una \u00fanica asignaci\u00f3n entre dos estructuras con vidas \u00fatiles independientes. El aliasing de \u0027trans_alpha\u0027 ha estado presente desde al menos libpng 1.0, y el aliasing de \u0027palette\u0027 desde al menos 1.2.1. Ambos afectan a todas las l\u00edneas de versiones anteriores: \u0027png_set_tRNS\u0027 establece \u0027png_ptr-\u0026gt;trans_alpha = info_ptr-\u0026gt;trans_alpha\u0027 (b\u00fafer de 256 bytes) y \u0027png_set_PLTE\u0027 establece \u0027info_ptr-\u0026gt;palette = png_ptr-\u0026gt;palette\u0027 (b\u00fafer de 768 bytes). En ambos casos, llamar a \u0027png_free_data\u0027 (con \u0027PNG_FREE_TRNS\u0027 o \u0027PNG_FREE_PLTE\u0027) libera el b\u00fafer a trav\u00e9s de \u0027info_ptr\u0027 mientras que el puntero \u0027png_ptr\u0027 correspondiente permanece colgante. Las funciones de transformaci\u00f3n de fila subsiguientes desreferencian y, en algunas rutas de c\u00f3digo, escriben en la memoria liberada. 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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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