A NULL pointer dereference is triggered due to an incorrect NULL check after memory allocation in the sixel_decode_raw and sixel_decode functions of libsixel. When the allocator returns NULL because of insufficient memory, the code mistakenly uses the always non‑NULL output pointer to write through a NULL pointer, causing the process using these public APIs to crash. The resulting effect is a denial‑of‑service toward any caller that encounters a low‑memory situation.

The vulnerability affects the libsixel library distributed by saitoha. Versions beginning with the first release that contains the decoding functions and continuing through 1.8.7‑r1 are susceptible. The issue is resolved in the 1.8.7‑r2 update, which introduces the correct NULL check and removes the crash path. Users installing earlier releases should upgrade to 1.8.7‑r2 or a subsequent version that includes the fix.

The CVSS base score is 2.5, placing the vulnerability in the low severity range. The EPSS score is not available, and the vulnerability is not listed in CISA's KEV catalog, indicating that no known exploits are widespread. Nonetheless, the flaw can be triggered during a low‑memory condition that any application invoking the public decoding APIs might experience, potentially causing repeated service interruptions. Exploitation requires the attacker to induce memory exhaustion or otherwise force a failure of the allocation; therefore, the likelihood depends on the environment’s memory management practices.