CVE-2017-7783: Mozilla Firefox

High severity, CVSS 7.5. EPSS: 14.1% chance of exploitation in the next 30 days.

If a long user name is used in a username/password combination in a site URL (such as " http://UserName:Password@example.com"), the resulting modal prompt will hang in a non-responsive state or crash, causing a denial of service. This vulnerability affects Firefox < 55.

Affected products

• Mozilla Firefox: before 55.0 (fixed in 55.0)

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