PyPI/urllib3 CVE-2021-33503: high 7.5, EPSS 3.27%

Catastrophic backtracking in URL authority parser when passed URL containing many @ characters

Action: Upgrade urllib3 to 1.26.5 or later.

pip install urllib3==1.26.5

Affected

Fixed versions

Sources

• osv: GHSA-q2q7-5pp4-w6pg
• https://github.com/urllib3/urllib3/security/advisories/GHSA-q2q7-5pp4-w6pg
• https://nvd.nist.gov/vuln/detail/CVE-2021-33503
• https://github.com/urllib3/urllib3/commit/2d4a3fee6de2fa45eb82169361918f759269b4ec
• https://github.com/urllib3/urllib3/commit/5b047b645f5f93900d5e2fc31230848c25eb1f5f#diff-52026d639119bf1e0364836b4e8a18bd9ed3c95c6ba39b26534a5057a65e35bbR65
• https://github.com/advisories/GHSA-q2q7-5pp4-w6pg
• https://github.com/pypa/advisory-database/tree/main/vulns/urllib3/PYSEC-2021-108.yaml
• https://github.com/urllib3/urllib3
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/6SCV7ZNAHS3E6PBFLJGENCDRDRWRZZ6W
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/FMUGWEAUYGGHTPPXT6YBD53WYXQGVV73
• https://security.gentoo.org/glsa/202107-36
• https://www.oracle.com/security-alerts/cpuoct2021.html

CVE-2021-33503 · published 2021-06-01T21:19:32Z · modified 2026-07-08T06:00:54.217433740Z · JSON