CVE-2021-33620: Debian Linux

Medium severity, CVSS 6.5. EPSS: 79.6% chance of exploitation in the next 30 days.

Squid before 4.15 and 5.x before 5.0.6 allows remote servers to cause a denial of service (affecting availability to all clients) via an HTTP response. The issue trigger is a header that can be expected to exist in HTTP traffic without any malicious intent by the server.

Affected products

• Debian Debian Linux: version 9.0 only
• Fedoraproject Fedora: version 33 only; version 34 only
• Squid-Cache Squid: before 4.15 (fixed in 4.15); from 5.0, before 5.0.6 (fixed in 5.0.6)

Published 2021-05-28. Last modified 2026-06-17.