Heap Buffer Overflow in SIXEL Encoder by Saitoha

CVE-2026-44636

What is CVE-2026-44636?

The libsixel library, an implementation of a SIXEL encoder/decoder, is susceptible to a vulnerability that facilitates a heap buffer overflow. This flaw arises from a signed integer overflow in the allocation size calculation during the execution of the sixel_encode_highcolor function. The current validation mechanism only checks that the specified width and height are greater than zero without imposing an upper limit. As a result, when the product of width and height exceeds INT_MAX (approximately 2.15 billion), it causes the allocation size to wrap into a smaller value. This allows the malloc function to allocate a buffer smaller than anticipated, leading to possible writes beyond the allocated memory, and potentially compromising system stability or integrity. The issue has been rectified in libsixel version 1.8.7-r2.

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