Buffer overflow in Saitoha Libsixel
CVE-2026-44636
libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. From to 1.8.7-r1, signed integer overflow in sixel_encode_highcolor's allocation size calculation can lead to a heap buffer overflow. The public sixel_encode entry point validates only that width and height are greater than zero, with no upper bound. width and height are multiplied as plain int when computing the allocation size for paletted_pixels and normalized_pixels. Any caller that asks libsixel to encode a pixel buffer with width times height greater than INT_MAX (about 2.15 billion) will hit a wrapped allocation size; under the right wrap, the malloc succeeds with a buffer much smaller than the encoder expects, and the encoder writes past the end of the heap allocation. This vulnerability is fixed in 1.8.7-r2.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.4 (High). Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.001 (2.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 3rd percentile — 2.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.001 · newest: 0.001 · change: +0.000
Affected products
- Saitoha Libsixel — versions >= 1.4.4, < 1.8.7-r2
Weakness classification (CWE)
References
- github.com/saitoha/libsixel/security/advisories/GHSA-hx93-w8p2-ffh5 (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-44636?
- CVE-2026-44636 is a high-severity vulnerability in Saitoha Libsixel, classified under Heap-based Buffer Overflow. CVSS score: 7.4/10. Published 2026-05-14.
- How severe is CVE-2026-44636?
- High severity. CVSS v3 base score is 7.4 out of 10.