CVE-2018-5134: Mozilla Firefox

High severity, CVSS 7.5. EPSS: 1.7% chance of exploitation in the next 30 days.

WebExtensions may use "view-source:" URLs to view local "file:" URL content, as well as content stored in "about:cache", bypassing restrictions that only allow WebExtensions to view specific content. This vulnerability affects Firefox < 59.

Affected products

• Mozilla Firefox: before 59.0 (fixed in 59.0)

Published 2018-06-11. Last modified 2026-06-17.