ACTIVELY EXPLOITED
CVE-2020-6820: Mozilla Firefox And Thunderbird Use-After-Free Vulnerability
| Vendor | Mozilla |
|---|---|
| Product | Firefox and Thunderbird |
| Actively exploited | Yes |
| Added to CISA KEV | 3 Nov 2021 |
| CISA federal deadline | 3 May 2022 |
| Weakness (CWE) | CWE-362 |
Required action (CISA's text)
Apply updates per vendor instructions.
Description (NVD)
Mozilla Firefox and Thunderbird contain a race condition vulnerability when handling a ReadableStream under certain conditions. The race condition creates a use-after-free vulnerability, causing unspecified impacts.
SOURCES
Other Mozilla flaws
- CVE-2010-3765: Mozilla Multiple Products Remote Code Execution Vulnerability
- CVE-2024-9680: Mozilla Firefox Use-After-Free Vulnerability
- CVE-2016-9079: Mozilla Firefox, Firefox ESR, and Thunderbird Use-After-Free Vulnerability
- CVE-2015-4495: Mozilla Firefox Security Feature Bypass Vulnerability
- CVE-2019-11708: Mozilla Firefox and Thunderbird Sandbox Escape Vulnerability
Data from NVD, CISA KEV, FIRST EPSS and vendor advisories. Updated 10 Nov 2026.