Reference page — cumulative record through Sunday, October 4, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2020-6820

CVE-2020-6820HIGH

Mozilla Firefox and Thunderbird

  AV  AC  PR  UI  S  C  I  A   CVSS    EPSS   %ile   KEV
   N   H   N   N  U  H  H  H    8.1   .0706   94.0   YES

AFFECTED
  Product      Versions       Fixed
  Thunderbird  unspecified –  —
  Firefox      unspecified –  —
  Firefox ESR  unspecified –  —

TIMELINE
  Jan 10  Reserved by mozilla
  Apr 24  Published (CNA: mozilla)
  Nov 3   Added to CISA KEV, remediation due 2022-05-03

CWE-362 · CNA: mozilla · CVSS v3.1 · 5 references · KEV due May 3, 2022

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.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
January 10, 2020	Reserved	Reserved by mozilla
April 24, 2020	Published	Published (CNA: mozilla)
November 3, 2021	KEV ADDED	Added to CISA KEV, remediation due 2022-05-03

Affected

Affected products and packages — 3 rows
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
Mozilla	Thunderbird	—	unspecified	—
Mozilla	Firefox	—	unspecified	—
Mozilla	Firefox ESR	—	unspecified	—

Weaknesses

CWE-362

References (5)

https://bugzilla.mozilla.org/show_bug.cgi?id=1626728 [x_refsource_MISC]
https://usn.ubuntu.com/4335-1/ [vendor-advisory, x_refsource_UBUNTU]
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-6820 [government-resource]
https://www.mozilla.org/security/advisories/mfsa2020-11/ [x_refsource_MISC]
https://www.mozilla.org/security/advisories/mfsa2020-14/ [x_refsource_MISC]

Authoritative record: CVE-2020-6820 at cve.org

Vendors: mozilla

Weaknesses: CWE-362

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2020-6820 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Sunday, October 4, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.