{"schema_version":"1.9.0","id":"GHSA-q2q7-5pp4-w6pg","published":"2021-06-01T21:19:32Z","modified":"2026-07-08T06:00:54.217433740Z","aliases":["CVE-2021-33503","PYSEC-2021-108"],"summary":"Catastrophic backtracking in URL authority parser when passed URL containing many @ characters","details":"### Impact\n\nWhen 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.\n\n\n### Patches\n\nThe issue has been fixed in urllib3 v1.26.5.\n\n### References\n\n- [CVE-2021-33503](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-33503)\n- [JVNVU#92413403 (English)](https://jvn.jp/en/vu/JVNVU92413403/)\n- [JVNVU#92413403 (Japanese)](https://jvn.jp/vu/JVNVU92413403/)\n- [urllib3 v1.26.5](https://github.com/urllib3/urllib3/releases/tag/1.26.5)\n\n### For more information\nIf you have any questions or comments about this advisory:\n* Ask in our [community Discord](https://discord.gg/urllib3)\n* Email [sethmichaellarson@gmail.com](mailto:sethmichaellarson@gmail.com)","affected":[{"package":{"name":"urllib3","ecosystem":"PyPI","purl":"pkg:pypi/urllib3"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"1.25.4"},{"fixed":"1.26.5"}]}],"versions":["1.25.10","1.25.11","1.25.4","1.25.5","1.25.6","1.25.7","1.25.8","1.25.9","1.26.0","1.26.1","1.26.2","1.26.3","1.26.4"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2021/06/GHSA-q2q7-5pp4-w6pg/GHSA-q2q7-5pp4-w6pg.json"}}],"references":[{"type":"WEB","url":"https://github.com/urllib3/urllib3/security/advisories/GHSA-q2q7-5pp4-w6pg"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-33503"},{"type":"WEB","url":"https://github.com/urllib3/urllib3/commit/2d4a3fee6de2fa45eb82169361918f759269b4ec"},{"type":"WEB","url":"https://github.com/urllib3/urllib3/commit/5b047b645f5f93900d5e2fc31230848c25eb1f5f#diff-52026d639119bf1e0364836b4e8a18bd9ed3c95c6ba39b26534a5057a65e35bbR65"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-q2q7-5pp4-w6pg"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/urllib3/PYSEC-2021-108.yaml"},{"type":"PACKAGE","url":"https://github.com/urllib3/urllib3"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/6SCV7ZNAHS3E6PBFLJGENCDRDRWRZZ6W"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/FMUGWEAUYGGHTPPXT6YBD53WYXQGVV73"},{"type":"WEB","url":"https://security.gentoo.org/glsa/202107-36"},{"type":"WEB","url":"https://www.oracle.com/security-alerts/cpuoct2021.html"}],"database_specific":{"cwe_ids":["CWE-400"],"github_reviewed":true,"github_reviewed_at":"2021-05-28T22:09:12Z","nvd_published_at":"2021-06-29T11:15:00Z","severity":"HIGH"},"severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"}]}