Back
CVE-2021-33503
An issue was discovered in urllib3 before 1.26.5. When provided with a URL containing many @ characters in the authority component, the…
High7.5EPSS 3.3%
- Published
- Updated
- Reserved
- Assigned by
- mitre
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| NVDNVD · Modified | 3.1 | High7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 3.3% · top 12% of all CVEs (6 Nov 2026)
Loading the EPSS history…
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.5.
Weakness
Affected products
n/a
- affected n/a
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- PyPIurllib3GHSA-q2q7-5pp4-w6pg (opens in a new tab)
References (6)
- FEDORA-2021-a6bde7ab18 (opens in a new tab)vendor-advisoryx_refsource_FEDORAx_transferred
- FEDORA-2021-9c5f3b8aae (opens in a new tab)vendor-advisoryx_refsource_FEDORAx_transferred
- GLSA-202107-36 (opens in a new tab)vendor-advisoryx_refsource_GENTOOx_transferred
- https://www.oracle.com/security-alerts/cpuoct2021.html (opens in a new tab)x_refsource_MISCx_transferred
- https://github.com/advisories/GHSA-q2q7-5pp4-w6pg (opens in a new tab)x_refsource_CONFIRMx_transferred
- https://github.com/urllib3/urllib3/commit/2d4a3fee6de2fa45eb82169361918f759269b4ec (opens in a new tab)x_refsource_CONFIRMx_transferred
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-q2q7-5pp4-w6pg (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2021-33503)Record last updated .