{"id":"CVE-2020-24240","url":"https://www.cyber-defence.io/tools/cve/CVE-2020-24240","generatedAt":"2026-10-27T20:22:07.333Z","title":"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.","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.","published":"2020-08-25T14:15:17.000Z","lastModified":"2026-06-17T03:05:20.000Z","status":"Modified","sourceIdentifier":"cve@mitre.org","cvss":{"version":"3.1","score":5.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H"},"cwe":["CWE-416"],"affected":["gnu/bison"],"epss":{"score":0.01265,"percentile":0.69527,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and a low EPSS score (1.26%). Track it; it rarely justifies an emergency change on its own."},"changes":[],"references":[{"url":"https://github.com/akimd/bison/commit/be95a4fe2951374676efc9454ffee8638faaf68d","tags":["Patch","Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://github.com/akimd/bison/compare/v3.7...v3.7.1","tags":["Third Party Advisory"],"source":"cve@mitre.org"},{"url":"https://lists.gnu.org/r/bug-bison/2020-07/msg00051.html","tags":["Mailing List","Vendor Advisory"],"source":"cve@mitre.org"},{"url":"https://github.com/akimd/bison/commit/be95a4fe2951374676efc9454ffee8638faaf68d","tags":["Patch","Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://github.com/akimd/bison/compare/v3.7...v3.7.1","tags":["Third Party Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"},{"url":"https://lists.gnu.org/r/bug-bison/2020-07/msg00051.html","tags":["Mailing List","Vendor Advisory"],"source":"af854a3a-2127-422b-91ae-364da2661108"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2020-24240","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}