urllib3 — security advisory

{
  "id": "1d07d13c2e4164bb1020e77e3920f2ba4231c999b8a8dadf765107a2c5f22823",
  "url": "https://osv.dev/vulnerability/PYSEC-2021-108",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "PYSEC-2021-108",
    "summary": "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.",
    "evidence": "osv:PYSEC-2021-108",
    "products": [
      {
        "name": {
          "value": "urllib3",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "1.26.5",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": [
          {
            "value": "1.25.10",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "1.25.11",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "1.25.4",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "1.25.5",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "1.25.6",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "1.25.7",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "1.25.8",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "1.25.9",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "1.26.0",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "1.26.1",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "1.26.2",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "1.26.3",
            "evidence": "/affected/0/versions"
          },
          {
            "value": "1.26.4",
            "evidence": "/affected/0/versions"
          }
        ]
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "PYSEC-2021-108",
      "aliases": [
        "CVE-2021-33503",
        "GHSA-q2q7-5pp4-w6pg",
        "PYSEC-2021-108"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/urllib3/urllib3",
              "type": "GIT",
              "events": [
                {
                  "introduced": "5b047b645f5f93900d5e2fc31230848c25eb1f5f"
                },
                {
                  "fixed": "2d4a3fee6de2fa45eb82169361918f759269b4ec"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "1.25.4"
                },
                {
                  "fixed": "1.26.5"
                }
              ]
            }
          ],
          "package": {
            "name": "urllib3",
            "purl": "pkg:pypi/urllib3",
            "ecosystem": "PyPI"
          },
          "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/pypa/advisory-database/blob/main/vulns/urllib3/PYSEC-2021-108.yaml"
          }
        }
      ],
      "modified": "2026-10-13T09:30:02.842062535Z",
      "provider": "osv",
      "references": [
        "https://github.com/advisories/GHSA-q2q7-5pp4-w6pg",
        "https://github.com/urllib3/urllib3/commit/2d4a3fee6de2fa45eb82169361918f759269b4ec"
      ]
    },
    "related_cves": [
      {
        "value": "CVE-2021-33503",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 307548,
  "published_at": "2021-06-29T11:15:00+00:00"
}