CVE-2021-23977: Mozilla Firefox

Medium severity, CVSS 5.3. EPSS: 0.9% chance of exploitation in the next 30 days.

Firefox for Android suffered from a time-of-check-time-of-use vulnerability that allowed a malicious application to read sensitive data from application directories. Note: This issue is only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 86.

Affected products

• Mozilla Firefox: before 86.0 (fixed in 86.0)

Published 2021-02-26. Last modified 2026-06-17.