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CVE-2026-33023— libsixel: Use-after-free in load_with_gdkpixbuf()

Quick assessment

Affected
saitoha libsixel
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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，该漏洞源于使用--with-gdk-pixbuf2选项构建时，load_with_gdkpixbuf函数存在释放后重用问题，可能导致处理特制图像时触发释放后重用，造成信息泄露、内存损坏或代码执行。

CVSS 7.8 · High EPSS 0.25% · P16

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-33023

Vulnerability Information
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Vulnerability Title
libsixel: Use-after-free in load_with_gdkpixbuf()
Source: CVE Program / CVE List V5
Vulnerability Description
libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. In versions 1.8.7 and prior, when built with the --with-gdk-pixbuf2 option, a use-after-free vulnerability exists in load_with_gdkpixbuf() in loader.c. The cleanup path manually frees the sixel_frame_t object and its internal buffers without consulting the reference count, even though the object was created via the refcounted constructor sixel_frame_new() and exposed to the public callback. A callback that calls sixel_frame_ref(frame) to retain a logically valid reference will hold a dangling pointer after sixel_helper_load_image_file() returns, and any subsequent access to the frame or its fields triggers a use-after-free confirmed by AddressSanitizer. The root cause is a consistency failure between two cleanup strategies in the same codebase: sixel_frame_unref() is used in load_with_builtin() but raw free() is used in load_with_gdkpixbuf(). An attacker supplying a crafted image to any application built against libsixel with gdk-pixbuf2 support can trigger this reliably, potentially leading to information disclosure, memory corruption, or code execution. This issue has been fixed in version 1.8.7-r1.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
释放后使用
Source: CVE Program / CVE List V5
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，该漏洞源于使用--with-gdk-pixbuf2选项构建时，load_with_gdkpixbuf函数存在释放后重用问题，可能导致处理特制图像时触发释放后重用，造成信息泄露、内存损坏或代码执行。
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

Vendor Product Affected Versions CPE Subscribe
saitoha libsixel < 1.8.7-r1 -

II. Public POCs for CVE-2026-33023

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III. Intelligence Information for CVE-2026-33023

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Vendor Advisories for CVE-2026-33023 (1)

Same Patch Batch · saitoha · 2026-04-14 · 5 CVEs total

CVE-2026-33021 7.3 HIGH libsixel: Use-after-free in sixel_encoder_encode_bytes()
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
Same vendor: saitoha
Same weakness: CWE-416

V. Comments for CVE-2026-33023

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