CVE-2019-12519: Canonical Ubuntu Linux

Critical severity, CVSS 9.8. EPSS: 6.7% chance of exploitation in the next 30 days.

An issue was discovered in Squid through 4.7. When handling the tag esi:when when ESI is enabled, Squid calls ESIExpression::Evaluate. This function uses a fixed stack buffer to hold the expression while it's being evaluated. When processing the expression, it could either evaluate the top of the stack, or add a new member to the stack. When adding a new member, there is no check to ensure that the stack won't overflow.

Affected products

• Canonical Ubuntu Linux: version 16.04 only; version 18.04 only; version 19.10 only; version 20.04 only
• Debian Debian Linux: version 9.0 only; version 10.0 only
• Opensuse Leap: version 15.1 only
• Squid-Cache Squid: from 3.0, up to and including 3.5.28; from 4.0, up to and including 4.10; from 5.0, up to and including 5.0.1

Published 2020-04-15. Last modified 2026-06-17.