Buffer overflow in Saitoha Libsixel
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.
Vulnerability class: Integer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.1 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H.
EPSS exploit prediction
EPSS: 0.002 (5.3th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 5th percentile — 5.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.000
Affected products
- Saitoha Libsixel — versions >= 0.11.0, < 1.8.7-r2
Weakness classification (CWE)
References
- github.com/saitoha/libsixel/security/advisories/GHSA-9jm7-77gr-qghv (Exploit, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-44637?
- CVE-2026-44637 is a high-severity vulnerability in Saitoha Libsixel, classified under Integer Overflow or Wraparound. CVSS score: 7.1/10. Published 2026-05-14.
- How severe is CVE-2026-44637?
- High severity. CVSS v3 base score is 7.1 out of 10.