CVE-2026-33020
Versions 1.8.7 and prior contain an integer overflow which leads to a heap buffer overflow via sixel_frame_convert_to_rgb888() in frame.c, where allocation size and pointer offset computations for palettised images (PAL1, PAL2, PAL4) are performed using…
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.21%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain an integer overflow which leads to a heap buffer overflow via sixel_frame_convert_to_rgb888() in frame.c, where allocation size and pointer offset computations for palettised images (PAL1, PAL2, PAL4) are performed using int arithmetic before casting to size_t. For images whose pixel count exceeds INT_MAX / 4, the overflow produces an undersized heap allocation for the conversion buffer and a negative pointer offset for the normalization sub-buffer, after which sixel_helper_normalize_pixelformat() writes the full image data starting from the invalid pointer, causing massive heap corruption confirmed by ASAN. An attacker providing a specially crafted large palettised PNG can corrupt the heap of the victim process, resulting in a reliable crash and potential arbitrary code execution. This issue has been fixed in version 1.8.7-r1.
- CVSS 3.1
- 7.1 HIGHCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
- EPSS
- 0.21% probability · 11th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-122, CWE-190
- Affected
- saitoha/libsixel
- Source
- security-advisories@github.com
References
- https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1Release Notes
- https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2pExploit, Vendor Advisory
- https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2pExploit, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.