Vulnerability in 8cc compiler

CERT Polska has received a report about vulnerability in 8cc compiler and participated in coordination of its disclosure.

The vulnerabilityCVE-2026-50643: 8cc is vulnerable to an Out‑of‑Bounds Read due to improper handling of#linedirectives and GNU linemarkers. The compiler accepts attacker-controlled filename and line number metadata and later uses it without validation when accessing source line arrays. By supplying invalid or oversized line numbers, an attacker can trigger out-of-bounds memory access and a crash.

Maintainer of this project was notified early about this vulnerability, but did not respond with the details of vulnerability or vulnerable version range. Version corresponding to the commit b480958 was tested and confirmed as vulnerable, other versions were not tested but might also be vulnerable.

We thank Michal Majchrowicz and Marcin Wyczechowski (AFINE) for the responsible vulnerability report.