Description
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.
Affected products
saitoha: libsixel
References2
- github.com/saitoha/libsixel/security/advisories/GHSA-9jm7-77gr-… ExploitVendor Advisory
- github.com/saitoha/libsixel/security/advisories/GHSA-9jm7-77gr-… ExploitVendor Advisory
Metrics
- CVSS 3.1
-
7.1
HIGH
Score source: CNA
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H - EPSS — exploit probability
- 0% percentile: 5 · as of 14 November 2026
- CWE
- CWE-190CWE-787
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