{
"id": "GHSA-q2q7-5pp4-w6pg",
"aliases": [
"CVE-2021-33503"
],
"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 [[email protected] ](mailto:[email protected] )",
"summary": "Catastrophic backtracking in URL authority parser when passed URL containing many @ characters",
"affected": [
{
"ranges": [
{
"type": "ECOSYSTEM",
"events": [
{
"introduced": "1.25.4"
},
{
"fixed": "1.26.5"
}
]
}
],
"package": {
"name": "urllib3",
"ecosystem": "PyPI"
}
}
],
"modified": "2026-06-09T13:01:45Z",
"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"
}
],
"published": "2021-06-01T21:19:32Z",
"references": [
{
"url": "https://github.com/urllib3/urllib3/security/advisories/GHSA-q2q7-5pp4-w6pg",
"type": "WEB"
},
{
"url": "https://nvd.nist.gov/vuln/detail/CVE-2021-33503",
"type": "ADVISORY"
},
{
"url": "https://github.com/urllib3/urllib3/commit/2d4a3fee6de2fa45eb82169361918f759269b4ec",
"type": "WEB"
},
{
"url": "https://github.com/urllib3/urllib3/commit/5b047b645f5f93900d5e2fc31230848c25eb1f5f#diff-52026d639119bf1e0364836b4e8a18bd9ed3c95c6ba39b26534a5057a65e35bbR65",
"type": "WEB"
},
{
"url": "https://github.com/advisories/GHSA-q2q7-5pp4-w6pg",
"type": "ADVISORY"
},
{
"url": "https://github.com/pypa/advisory-database/tree/main/vulns/urllib3/PYSEC-2021-108.yaml",
"type": "WEB"
},
{
"url": "https://github.com/urllib3/urllib3",
"type": "PACKAGE"
},
{
"url": "https://lists.fedoraproject.org/archives/list/[email protected] /message/6SCV7ZNAHS3E6PBFLJGENCDRDRWRZZ6W",
"type": "WEB"
},
{
"url": "https://lists.fedoraproject.org/archives/list/[email protected] /message/FMUGWEAUYGGHTPPXT6YBD53WYXQGVV73",
"type": "WEB"
},
{
"url": "https://security.gentoo.org/glsa/202107-36",
"type": "WEB"
},
{
"url": "https://www.oracle.com/security-alerts/cpuoct2021.html",
"type": "WEB"
}
],
"schema_version": "1.4.0",
"database_specific": {
"cwe_ids": [
"CWE-400"
],
"severity": "HIGH",
"github_reviewed": true,
"nvd_published_at": "2021-06-29T11:15:00Z",
"github_reviewed_at": "2021-05-28T22:09:12Z"
}
}