{"id":"CVE-2021-3828","aliases":["GHSA-2ww3-fxvq-293j","PYSEC-2021-356"],"url":"https://o3.security/vulnerability/CVE-2021-3828","summary":"NLTK Vulnerable to REDoS","details":"nltk is vulnerable to Inefficient Regular Expression Complexity","published":"2021-09-27T13:15:07.993Z","modified":"2026-07-09T01:31:40.287799Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":{"score":0.01703,"percentile":0.75112,"asOf":"2026-08-23"},"cisaKev":null,"exploitsKnown":1,"affectedPackages":[{"ecosystem":"PyPI","name":"nltk","fixedVersion":"3.6.4"}],"fix":{"url":"https://github.com/nltk/nltk/commit/277711ab1dec729e626b27aab6fa35ea5efbd7e6","label":"nltk/nltk@277711a"},"references":[{"type":"FIX","url":"https://github.com/nltk/nltk/commit/277711ab1dec729e626b27aab6fa35ea5efbd7e6"},{"type":"FIX","url":"https://huntr.dev/bounties/d19aed43-75bc-4a03-91a0-4d0bb516bc32"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-09T01:31:40.287799Z"}}