CVE-2020-24240: GNU Bison

Medium severity, CVSS 5.5. EPSS: 1.3% chance of exploitation in the next 30 days.

GNU Bison before 3.7.1 has a use-after-free in _obstack_free in lib/obstack.c (called from gram_lex) when a '\0' byte is encountered. NOTE: there is a risk only if Bison is used with untrusted input, and the observed bug happens to cause unsafe behavior with a specific compiler/architecture. The bug report was intended to show that a crash may occur in Bison itself, not that a crash may occur in code that is generated by Bison.

Affected products

• GNU Bison: version 3.7 only

Published 2020-08-25. Last modified 2026-06-17.