CVE-2025-10859: Mozilla Firefox

Medium severity, CVSS 4.0. EPSS: 0.1% chance of exploitation in the next 30 days.

Cookie storage for non-HTML temporary documents was being shared incorrectly with normal browsing content, allowing information from private tabs to escape Incognito mode even after the user closed all tabs. This vulnerability was fixed in Firefox for iOS 143.1.

Affected products

• Mozilla Firefox: before 143.1.0 (fixed in 143.1.0)

Published 2025-09-30. Last modified 2026-10-05.