CVE-2026-44637

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. From to 1.8.7-r1, a signed integer overflow in the SIXEL parser's image-buffer doubling loop can lead to an out-of-bounds heap write in sixel_decode_raw_impl. context->pos_x grows by repeat_count on every sixel character with no upper bound check. Once pos_x approaches INT_MAX, the expression "pos_x + repeat_count" used to size the image buffer overflows signed int. Depending on how the overflow wraps, the resize check that should reject oversized buffers can be bypassed, after which a subsequent write computes a large attacker-influenced offset into image->data and writes past the allocation. Reachable from any caller that decodes attacker-supplied SIXEL data, including img2sixel. This vulnerability is fixed in 1.8.7-r2.

• CWE-190
• CWE-787
• CWE-787

• https://github.com/saitoha/libsixel/security/advisories/GHSA-9jm7-77gr-qghvExploit, Vendor Advisory
• https://github.com/saitoha/libsixel/security/advisories/GHSA-9jm7-77gr-qghvExploit, Vendor Advisory

Published

May 14, 2026

Last Modified

Jun 17, 2026

Status

Analyzed

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