High
libsixel — security advisory
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.
- Products
- libsixel
- Affected versions
- 1.10.3-2, 1.10.3-3, 1.10.3-3build1, 1.10.5-1, 1.10.5-1build1, 1.4.2-1, 1.5.2-2, 1.7.3-1, 1.8.2-1, 1.8.2-2.1, 1.8.6-2, 1:1.8.7-r2-1
- Fixed versions
- Not specified
- CVEs
- CVE-2026-44637
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 02:13 UTC · Revision 1
Source evidence
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.
osv:UBUNTU-CVE-2026-44637
libsixel
Fixed versions: Not specified
libsixel
Fixed versions: Not specified
libsixel
Fixed versions: Not specified
libsixel
Fixed versions: Not specified
libsixel
Fixed versions: Not specified
libsixel
Fixed versions: Not specified
libsixel
Fixed versions: Not specified
libsixel
Fixed versions: Not specified
Complete source record
{
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"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-44637",
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"summary": "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.",
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"modified": "2026-10-17T12:58:21.638775006Z",
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"https://github.com/saitoha/libsixel/security/advisories/GHSA-9jm7-77gr-qghv"
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"published_at": "2026-05-14T20:17:00+00:00"
}