CVE-2026-33021
CVE-2026-33021 · libsixel: Use-after-free in sixel_encoder_encode_bytes()
This page contains facts from public vulnerability sources. Check the original advisory before updating.
libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain a use-after-free vulnerability in sixel_encoder_encode_bytes() because sixel_frame_init() stores the caller-owned pixel buffer pointer directly in frame->pixels without making a defensive copy. When a resize operation is triggered, sixel_frame_convert_to_rgb888() unconditionally frees this caller-owned buffer and replaces it with a new internal allocation, leaving the caller with a dangling pointer. Any subsequent access to the original buffer by the caller constitutes a use-after-free, confirmed by AddressSanitizer. An attacker who controls incoming frames can trigger this bug repeatedly and predictably, resulting in a reliable crash with potential for code execution. This issue has been fixed in version 1.8.7-r1.
CVSS 7.3 · High · EPSS 0.2% · Fix available
- Published
- Updated
Stack: system
Affected products and versions
libsixel
- Versions
- < 1.8.7-r1: Affected
No fix published
libsixel Debian:12
- 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
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published
libsixel Debian:13
- Versions
- 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
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published
libsixel Debian:14
- Versions
- 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
- Affected ranges
- ECOSYSTEM: < 1:1.8.7-r2-1
Update to 1:1.8.7-r2-1
libsixel Ubuntu:16.04:LTS
- Versions
- 1.4.2-1
- 1.5.2-2
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published
libsixel Ubuntu:18.04:LTS
- Versions
- 1.5.2-2
- 1.7.3-1
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published
libsixel Ubuntu:20.04:LTS
- Versions
- 1.8.2-1
- 1.8.2-2.1
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published
libsixel Ubuntu:22.04:LTS
- Versions
- 1.8.6-2
- 1.10.3-2
- 1.10.3-3
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published
libsixel Ubuntu:24.04:LTS
- Versions
- 1.10.3-3
- 1.10.3-3build1
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published
libsixel Ubuntu:25.10
- Versions
- 1.10.5-1
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published
libsixel Ubuntu:26.10
- Versions
- 1.10.5-1build1
- 1:1.8.7-r2-1
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published
libsixel Ubuntu:26.04:LTS
- Versions
- 1.10.5-1
- 1.10.5-1build1
- Affected ranges
- ECOSYSTEM: (−∞, +∞)
No fix published