CVE-2026-33021— libsixel: Use-after-free in sixel_encoder_encode_bytes()
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I. Basic Information for CVE-2026-33021
Vulnerability Information
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Vulnerability Title
libsixel: Use-after-free in sixel_encoder_encode_bytes()
Source: NVD (National Vulnerability Database)
Vulnerability Description
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.
Source: NVD (National Vulnerability Database)
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
Source: NVD (National Vulnerability Database)
Vulnerability Type
释放后使用
Source: NVD (National Vulnerability Database)
Vulnerability Title
libsixel 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
libsixel是Hayaki Saito个人开发者的一个为DEC SIXEL图形和其他转换器程序提供编码/解码实现的软件包。 libsixel 1.8.7及之前版本存在资源管理错误漏洞，该漏洞源于sixel_encoder_encode_bytes函数存在释放后重用问题，可能导致攻击者控制传入帧时触发释放后重用，造成崩溃或代码执行。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
II. Public POCs for CVE-2026-33021
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Same Patch Batch · saitoha · 2026-04-14 · 5 CVEs total
| CVE-2026-33023 | 7.8 HIGH | libsixel: Use-after-free in load_with_gdkpixbuf() |
| CVE-2026-33019 | 7.1 HIGH | libsixel: Integer overflow leads to Out-of-bounds Read in img2sixel |
| CVE-2026-33020 | 7.1 HIGH | libsixel: Integer Overflow in write_png_to_file() leads to Heap-based Buffer Overflow |
| CVE-2026-33018 | 7.0 HIGH | libsixel: Use-After-Free in load_gif() |
IV. Related Vulnerabilities
Same product: libsixel
- CVE-2026-33023
libsixel: Use-after-free in load_with_gdkpixbuf() - CVE-2026-33020
libsixel: Integer Overflow in write_png_to_file() leads to H - CVE-2026-33019
libsixel: Integer overflow leads to Out-of-bounds Read in im - CVE-2026-33018
libsixel: Use-After-Free in load_gif() - CVE-2025-9300
saitoha libsixel img2sixel encoder.c sixel_debug_print_palet
Same vendor: saitoha
- CVE-2026-33023
libsixel: Use-after-free in load_with_gdkpixbuf() - CVE-2026-33020
libsixel: Integer Overflow in write_png_to_file() leads to H - CVE-2026-33019
libsixel: Integer overflow leads to Out-of-bounds Read in im - CVE-2026-33018
libsixel: Use-After-Free in load_gif() - CVE-2025-9300
saitoha libsixel img2sixel encoder.c sixel_debug_print_palet
V. Comments for CVE-2026-33021
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