CVE-2018-5138: Mozilla Firefox

Medium severity, CVSS 5.3. EPSS: 1.1% chance of exploitation in the next 30 days.

A spoofing vulnerability can occur when a malicious site with an extremely long domain name is opened in an Android Custom Tab (a browser panel inside another app) and the default browser is Firefox for Android. This could allow an attacker to spoof which page is actually loaded and in use. Note: this issue only affects Firefox for Android. Other versions and operating systems are unaffected. 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.