CVE-2020-15810: Canonical Ubuntu Linux

Medium severity, CVSS 6.5. EPSS: 2.4% chance of exploitation in the next 30 days.

An issue was discovered in Squid before 4.13 and 5.x before 5.0.4. Due to incorrect data validation, HTTP Request Smuggling attacks may succeed against HTTP and HTTPS traffic. This leads to cache poisoning. This allows any client, including browser scripts, to bypass local security and poison the proxy cache and any downstream caches with content from an arbitrary source. When configured for relaxed header parsing (the default), Squid relays headers containing whitespace characters to upstream servers. When this occurs as a prefix to a Content-Length header, the frame length specified will be ignored by Squid (allowing for a conflicting length to be used from another Content-Length header) but relayed upstream.

Affected products

• Canonical Ubuntu Linux: version 16.04 only; version 18.04 only; version 20.04 only
• Debian Debian Linux: version 9.0 only; version 10.0 only
• Fedoraproject Fedora: version 31 only; version 32 only; version 33 only
• Opensuse Leap: version 15.1 only; version 15.2 only
• Squid-Cache Squid: before 4.13 (fixed in 4.13); from 5.0, before 5.0.4 (fixed in 5.0.4)

Published 2020-09-02. Last modified 2026-06-17.