CVE-2019-12523: Canonical Ubuntu Linux

Critical severity, CVSS 9.1. EPSS: 4.3% chance of exploitation in the next 30 days.

An issue was discovered in Squid before 4.9. When handling a URN request, a corresponding HTTP request is made. This HTTP request doesn't go through the access checks that incoming HTTP requests go through. This causes all access checks to be bypassed and allows access to restricted HTTP servers, e.g., an attacker can connect to HTTP servers that only listen on localhost.

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 9.0 only; version 10.0 only
• Fedoraproject Fedora: version 30 only; version 31 only
• Opensuse Leap: version 15.0 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.