CVE-2020-6820
Mozilla Firefox And Thunderbird Use-After-Free Vulnerability
Does this matter?
Known to be exploited in the wild (CISA KEV, CISA remediation deadline 3 May 2022). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.
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.
- CVSS 3.1
- 8.1 HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 7.06% probability · 94th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Listed 3 November 2021 · due 3 May 2022
- Weakness
- CWE-362
- Affected
- mozilla/firefox · mozilla/thunderbird
- Source
- security@mozilla.org
EPSS 7.1% since 30 October 2026; no change recorded yet. The dashed line is the ten per cent mark our analysts treat as “patch before the next change window”. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
CISA notes
Apply updates per vendor instructions. https://nvd.nist.gov/vuln/detail/CVE-2020-6820
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=1626728Issue 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://bugzilla.mozilla.org/show_bug.cgi?id=1626728Issue 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-2020-6820US Government Resource
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.