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CVE-2026-33018— libsixel: Use-After-Free in load_gif()

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load_gif函数存在释放后重用问题，可能导致处理用户提供的动画GIF时发生堆释放后重用，造成崩溃或代码执行。

CVSS 7.0 · High EPSS 0.19% · P8

Possible ATT&CK Techniques 1 AI

T1203 · Exploitation for Client Execution
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I. Basic Information for CVE-2026-33018

Vulnerability Information
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Vulnerability Title
libsixel: Use-After-Free in load_gif()
Source: CVE Program / CVE List V5
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 via the load_gif() function in fromgif.c, where a single sixel_frame_t object is reused across all frames of an animated GIF and gif_init_frame() unconditionally frees and reallocates frame->pixels between frames without consulting the object's reference count. Because the public API explicitly provides sixel_frame_ref() to retain a frame and sixel_frame_get_pixels() to access the raw pixel buffer, a callback following this documented usage pattern will hold a dangling pointer after the second frame is decoded, resulting in a heap use-after-free confirmed by ASAN. Any application using sixel_helper_load_image_file() with a multi-frame callback to process user-supplied animated GIFs is affected, with a reliable crash as the minimum impact and potential for 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:H/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load_gif函数存在释放后重用问题，可能导致处理用户提供的动画GIF时发生堆释放后重用，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

Vendor Product Affected Versions CPE Subscribe
saitoha libsixel < 1.8.7-rc1 -

II. Public POCs for CVE-2026-33018

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III. Intelligence Information for CVE-2026-33018

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Vendor Advisories for CVE-2026-33018 (1)

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-2026-33021 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

IV. Related Vulnerabilities

Same product: libsixel
Same vendor: saitoha
Same weakness: CWE-416

V. Comments for CVE-2026-33018

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