7.1 CVE-2026-33020

Enriched by CISA
 

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.
https://nvd.nist.gov/vuln/detail/CVE-2026-33020

Categories

CWE-122 : Heap-based Buffer Overflow
A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc(). Fuzz testing (fuzzing) is a powerful technique for generating large numbers of diverse inputs - either randomly or algorithmically - and dynamically invoking the code with those inputs. Even with random inputs, it is often capable of generating unexpected results such as crashes, memory corruption, or resource consumption. Fuzzing effectively produces repeatable test cases that clearly indicate bugs, which helps developers to diagnose the issues. Use tools that are integrated duringcompilation to insert runtime error-checking mechanismsrelated to memory safety errors, such as AddressSanitizer(ASan) for C/C++ [REF-1518]. Pre-design: Use a language or compiler that performs automatic bounds checking. Use an abstraction library to abstract away risky APIs. Not a complete solution. Implement and perform bounds checking on input. Do not use dangerous functions such as gets. Look for their safe equivalent, which checks for the boundary. Use OS-level preventative functionality. This is not a complete solution, but it provides some defense in depth. Chain: Javascript engine code does not perform a length check (CWE-1284) leading to integer overflow (CWE-190) causing allocation of smaller buffer than expected (CWE-131) resulting in a heap-based buffer overflow (CWE-122) Chain: in a web browser, an unsigned 64-bit integer is forcibly cast to a 32-bit integer (CWE-681) and potentially leading to an integer overflow (CWE-190). If an integer overflow occurs, this can cause heap memory corruption (CWE-122) Chain: integer signedness error (CWE-195) passes signed comparison, leading to heap overflow (CWE-122) Chain: product does not handle when an input string is not NULL terminated (CWE-170), leading to buffer over-read (CWE-125) or heap-based buffer overflow (CWE-122). Chain: machine-learning product can have a heap-basedbuffer overflow (CWE-122) when some integer-oriented bounds arecalculated by using ceiling() and floor() on floating point values(CWE-1339) Chain: integer overflow (CWE-190) causes a negative signed value, which later bypasses a maximum-only check (CWE-839), leading to heap-based buffer overflow (CWE-122).

References


 

AFFECTED (from MITRE)

Vendor Product Versions
saitoha libsixel
  • < 1.8.7-r1 [affected]
© 2022 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation.

CPE

cpe start end

REMEDIATION


EXPLOITS

Exploit-db.com

id description date
No known exploits

POC Github

Url
No known exploits

Other Nist (github, ...)

Url
No known exploits

CAPEC

Common Attack Pattern Enumerations and Classifications

id description severity
92 Forced Integer Overflow
High