CVE-2019-18678: Canonical Ubuntu Linux

Medium severity, CVSS 5.3. EPSS: 6.2% chance of exploitation in the next 30 days.

An issue was discovered in Squid 3.x and 4.x through 4.8. It allows attackers to smuggle HTTP requests through frontend software to a Squid instance that splits the HTTP Request pipeline differently. The resulting Response messages corrupt caches (between a client and Squid) with attacker-controlled content at arbitrary URLs. Effects are isolated to software between the attacker client and Squid. There are no effects on Squid itself, nor on any upstream servers. The issue is related to a request header containing whitespace between a header name and a colon.

Affected products

• Canonical Ubuntu Linux: version 16.04 only; version 18.04 only; version 19.04 only; version 19.10 only
• Debian Debian Linux: version 8.0 only
• Fedoraproject Fedora: version 30 only; version 31 only
• Squid-Cache Squid: from 3.0, up to and including 3.5.28; from 4.0, up to and including 4.8

Published 2019-11-26. Last modified 2026-06-17.