CVE-2026-44637: saitoha libsixel Integer Overflow or Wraparound

Vulnerability summary

CVE-2026-44637 is a high (CVSS 7.1) Integer Overflow or Wraparound vulnerability in saitoha libsixel. EPSS estimates a 0.17% chance of exploitation in the next 30 days, higher than 5.5% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 14-05-2026
   PublishedVulnerability first disclosed.
2. 15-05-2026
   Last modifiedVulnerability information updated.

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.

• CWE-190Integer Overflow or WraparoundThe product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.
• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.