CVE-2021-33503: Fedoraproject Fedora

High severity, CVSS 7.5. EPSS: 3.3% chance of exploitation in the next 30 days.

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.

Affected products

• Fedoraproject Fedora: version 33 only; version 34 only
• Oracle Enterprise Manager Ops Center: version 12.4.0.0 only
• Oracle Instantis Enterprisetrack: version 17.1 only; version 17.2 only; version 17.3 only
• Oracle ZFS Storage Appliance Kit: version 8.8 only
• Python URLLIB3: from 1.25.4, before 1.26.5 (fixed in 1.26.5)

Published 2021-06-29. Last modified 2026-06-17.