CVE-2020-24240

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2020-08-25 · updated 2026-06-17
Weakness: CWE-416

Description

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: 3.7

References

https://github.com/akimd/bison/commit/be95a4fe2951374676efc9454ffee8638faaf68d
https://github.com/akimd/bison/compare/v3.7...v3.7.1
https://lists.gnu.org/r/bug-bison/2020-07/msg00051.html
https://github.com/akimd/bison/commit/be95a4fe2951374676efc9454ffee8638faaf68d
https://github.com/akimd/bison/compare/v3.7...v3.7.1
https://lists.gnu.org/r/bug-bison/2020-07/msg00051.html

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