CVE-2026-44637
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.16%). 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. 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.
- 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
- 0.16% probability · 5th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-190, CWE-787
- Affected
- saitoha/libsixel
- Source
- security-advisories@github.com
References
- 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
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.