{"cve":"CVE-2021-33503","nvd":{"published":"2021-06-29T11:15:07.847","modified":"2026-06-17T03:54:41.387","status":"Modified","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-400"],"references":["https://github.com/advisories/GHSA-q2q7-5pp4-w6pg","https://github.com/urllib3/urllib3/commit/2d4a3fee6de2fa45eb82169361918f759269b4ec","https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/6SCV7ZNAHS3E6PBFLJGENCDRDRWRZZ6W/","https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/FMUGWEAUYGGHTPPXT6YBD53WYXQGVV73/","https://security.gentoo.org/glsa/202107-36"],"products":["fedoraproject:fedora","oracle:enterprise_manager_ops_center","oracle:instantis_enterprisetrack","oracle:zfs_storage_appliance_kit","python:urllib3"],"source":"nvd","synced_at":"2026-10-19T21:20:07.141963181+00:00"},"epss":{"cve":"CVE-2021-33503","score":0.03273,"percentile":0.88416,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-q2q7-5pp4-w6pg","url":"https://osv.dev/vulnerability/GHSA-q2q7-5pp4-w6pg","summary":"Catastrophic backtracking in URL authority parser when passed URL containing many @ characters","modified":"2026-07-08T06:00:54.217433740Z","packages":[{"ecosystem":"PyPI","name":"urllib3","purl":"pkg:pypi/urllib3","ranges":[">=1.25.4 <1.26.5"],"fixed":["1.26.5"]}]},{"id":"PYSEC-2021-108","url":"https://osv.dev/vulnerability/PYSEC-2021-108","summary":"","modified":"2026-10-13T09:30:02.842062535Z","packages":[{"ecosystem":"PyPI","name":"urllib3","purl":"pkg:pypi/urllib3","ranges":[">=1.25.4 <1.26.5"],"fixed":["1.26.5"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}