{"id":"CVE-2021-33503","aliases":["GHSA-q2q7-5pp4-w6pg","PYSEC-2021-108"],"url":"https://o3.security/vulnerability/CVE-2021-33503","summary":"Catastrophic backtracking in URL authority parser when passed URL containing many @ characters","details":"An issue was discovered in urllib3 before 1.26.5. When provided with a URL containing many @ characters in the authority component, the authority regular expression exhibits catastrophic backtracking, causing a denial of service if a URL were passed as a parameter or redirected to via an HTTP redirect.","published":"2021-06-29T11:15:07.847Z","modified":"2026-08-07T11:49:15.119993913Z","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":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"PyPI","name":"urllib3","fixedVersion":"1.26.5"}],"fix":{"url":"https://github.com/urllib3/urllib3/commit/2d4a3fee6de2fa45eb82169361918f759269b4ec","label":"urllib3/urllib3@2d4a3fe"},"references":[{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/6SCV7ZNAHS3E6PBFLJGENCDRDRWRZZ6W/"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FMUGWEAUYGGHTPPXT6YBD53WYXQGVV73/"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-q2q7-5pp4-w6pg"},{"type":"ADVISORY","url":"https://security.gentoo.org/glsa/202107-36"},{"type":"FIX","url":"https://github.com/urllib3/urllib3/commit/2d4a3fee6de2fa45eb82169361918f759269b4ec"},{"type":"FIX","url":"https://www.oracle.com/security-alerts/cpuoct2021.html"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T11:49:15.119993913Z"}}