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
- 1.10.3-3, 1.10.5-1, 1:1.8.7-1, 1:1.8.7-2, 1:1.8.7-3, 1:1.8.7-4, 1:1.8.7-5, 1:1.8.7-6, 1:1.8.7-r2-1
- Fixed versions
- 1:1.8.7-r2-1
- CVEs
- CVE-2026-44637
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 1 Nov 2026, 17:37 UTC · Revision 2
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:DEBIAN-CVE-2026-44637
libsixel
Fixed versions: Not specified
libsixel
Fixed versions: Not specified
libsixel
Fixed versions: 1:1.8.7-r2-1
Complete source record
{
"id": "d2c2287a21556ac0a83f73b15af43e3de70b57ad6284617301790176cd4b84f1",
"url": "https://osv.dev/vulnerability/DEBIAN-CVE-2026-44637",
"method": "structured",
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"title": "DEBIAN-CVE-2026-44637",
"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.",
"evidence": "osv:DEBIAN-CVE-2026-44637",
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"modified": "2026-10-27T09:47:33.701891810Z",
"provider": "osv",
"upstream": [
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],
"references": [
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"evidence": "/upstream"
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"source_id": "core-osv",
"document_id": 460929,
"published_at": "2026-05-14T20:17:08.847+00:00"
}