CVEs / CVE-2020-6820
CVE-2020-6820: Mozilla Firefox And Thunderbird Use-After-Free Vulnerability
- Known exploited in the CISA KEV catalog since 3 Nov 2021
- high 8.1 CVSS 3.1 (NVD)
- EPSS 7.06% chance of exploitation in the next 30 days, higher than 94% of CVEs (30 Oct 2026)
- Last changed at its sources
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Summary
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.
Description
Under certain conditions, when handling a ReadableStream, a race condition can cause a use-after-free. We are aware of targeted attacks in the wild abusing this flaw. This vulnerability affects Thunderbird < 68.7.0, Firefox < 74.0.1, and Firefox ESR < 68.6.1.
Affected and fixed versions
| Product | Affected | Fixed in |
|---|---|---|
| Mozilla Thunderbird | from unspecified, before 68.7.0 | 68.7.0 |
| Mozilla Firefox | from unspecified, before 74.0.1 | 74.0.1 |
| Mozilla Firefox ESR | from unspecified, before 68.6.1 | 68.6.1 |
Exploitation
| In CISA KEV since | 3 Nov 2021 |
|---|---|
| Due date for US federal agencies | 3 May 2022 |
| Used in ransomware campaigns | Unknown |
| Required action | Apply updates per vendor instructions. |
Severity
| CVSS 3.1 | 8.1 highCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:HScored by NVD |
|---|---|
| Weakness | CWE-362 |
References
- CVE-2020-6820 on NVD
- CVE-2020-6820 in the CISA KEV catalog
- CVE-2020-6820 on OSV
- https://bugzilla.mozilla.org/show_bug.cgi?id=1626728 Issue Tracking, Permissions Required
- https://usn.ubuntu.com/4335-1/ Third Party Advisory
- https://www.mozilla.org/security/advisories/mfsa2020-11/ Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2020-14/ Vendor Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-6820 US Government Resource
Sources
Exploitation status from the CISA Known Exploited Vulnerabilities catalog. EPSS scores from FIRST. Descriptions, severity and references from the National Vulnerability Database. Open-source package versions from OSV (CC-BY 4.0). Text is shown as each source states it; Stackurity does not edit it. Check the vendor's advisory before acting.
This product uses data from the NVD API but is not endorsed or certified by the NVD.