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CVE-2026-44636— libsixel: integer overflow in encoder

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-r1及之前版本存在安全漏洞，该漏洞源于sixel_encode_highcolor分配大小计算中的有符号整数溢出，可能导致堆缓冲区溢出。

CVSS 7.4 · High EPSS 0.14% · P3

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
saitoha libsixel >= 1.4.4, < 1.8.7-r2 affected
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I. Basic Information for CVE-2026-44636

Vulnerability Information
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Vulnerability Title
libsixel: integer overflow in encoder
Source: CVE Program / CVE List V5
Vulnerability Description
libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. From to 1.8.7-r1, signed integer overflow in sixel_encode_highcolor's allocation size calculation can lead to a heap buffer overflow. The public sixel_encode entry point validates only that width and height are greater than zero, with no upper bound. width and height are multiplied as plain int when computing the allocation size for paletted_pixels and normalized_pixels. Any caller that asks libsixel to encode a pixel buffer with width times height greater than INT_MAX (about 2.15 billion) will hit a wrapped allocation size; under the right wrap, the malloc succeeds with a buffer much smaller than the encoder expects, and the encoder writes past the end of the heap allocation. This vulnerability is fixed in 1.8.7-r2.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
堆缓冲区溢出
Source: CVE Program / CVE List V5
Vulnerability Title
libsixel 安全漏洞
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-r1及之前版本存在安全漏洞，该漏洞源于sixel_encode_highcolor分配大小计算中的有符号整数溢出，可能导致堆缓冲区溢出。
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 >= 1.4.4, < 1.8.7-r2 -

II. Public POCs for CVE-2026-44636

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III. Intelligence Information for CVE-2026-44636

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Vendor Advisories for CVE-2026-44636 (1)

Same Patch Batch · saitoha · 2026-05-14 · 3 CVEs total

CVE-2026-44637 7.1 HIGH libsixel: integer overflow in parser
CVE-2026-44638 2.5 LOW libsixel: NULL pointer dereference

IV. Related Vulnerabilities

Same product: libsixel
Same vendor: saitoha
Same weakness: CWE-122

V. Comments for CVE-2026-44636

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