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I. Basic Information for CVE-2026-33020
Vulnerability Information

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Vulnerability Title
libsixel: Integer Overflow in write_png_to_file() leads to Heap-based Buffer Overflow
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 an integer overflow which leads to a heap buffer overflow via sixel_frame_convert_to_rgb888() in frame.c, where allocation size and pointer offset computations for palettised images (PAL1, PAL2, PAL4) are performed using int arithmetic before casting to size_t. For images whose pixel count exceeds INT_MAX / 4, the overflow produces an undersized heap allocation for the conversion buffer and a negative pointer offset for the normalization sub-buffer, after which sixel_helper_normalize_pixelformat() writes the full image data starting from the invalid pointer, causing massive heap corruption confirmed by ASAN. An attacker providing a specially crafted large palettised PNG can corrupt the heap of the victim process, resulting in a reliable crash and potential arbitrary 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:R/S:U/C:N/I:H/A:H
Source: NVD (National Vulnerability Database)
Vulnerability Type
堆缓冲区溢出
Source: NVD (National Vulnerability Database)
Vulnerability Title
libsixel 输入验证错误漏洞
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及之前版本存在输入验证错误漏洞,该漏洞源于sixel_frame_convert_to_rgb888函数存在整数溢出,可能导致堆缓冲区溢出,造成堆损坏、崩溃或任意代码执行。
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
VendorProductAffected VersionsCPESubscribe
saitohalibsixel < 1.8.7-r1 -
II. Public POCs for CVE-2026-33020
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III. Intelligence Information for CVE-2026-33020
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