CVE-2017-7789: Mozilla Firefox

Medium severity, CVSS 5.3. EPSS: 1.8% chance of exploitation in the next 30 days.

If a server sends two Strict-Transport-Security (STS) headers for a single connection, they will be rejected as invalid and HTTP Strict Transport Security (HSTS) will not be enabled for the connection. 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.