CVE-2020-6820

CRITICALNVD 8.19.0▲
EchelonGraph scoreHIGH confidence

Score elevated to 9.0 because this CVE is listed on the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), indicating real-world exploitation has been confirmed by US federal agencies. NVD baseline CVSS 8.1 retained for reference. Confidence: HIGH.

Triggered by: CISA KEV (actively exploited)
Sources: cisa_kev, epss, ghsa, nvd
Trending — 5 sources updated this weekExploited in the wild
9.0EG
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS PROB: 7%CVSS: 8.1Exploit: cisa kev · ssvc activeExposed: 0

A fix is available — apply it.

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 v3
8.1
EG Score
9.0(high)
EG Risk
81(Attend)
EG Risk 81/100SSVC: Attend

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity90% × 45%
Exploitation100% × 40%
Automatability0% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
7%
EPSS %ILE
94%
KEV
⚠ Exploited

Published

April 24, 2020

Last Modified

November 4, 2025

Advisory Details (4)

Auto-updated Jun 3, 2026
⚠️ Active exploitation confirmed. Patch available. Sources: cisa.
cisa Patch Available🔴 Active Exploitation

Known Exploited Vulnerabilities Catalog | CISA

Known Exploited Vulnerabilities Catalog | CISA. Listed in CISA Known Exploited Vulnerabilities catalog.

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-6820
generic

Security Vulnerabilities fixed in Thunderbird 68.7.0 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2020-14/
generic🔴 Active Exploitation

Security Vulnerabilities fixed in Firefox 74.0.1 and Firefox ESR 68.6.1 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2020-11/
generic🔴 Active Exploitation

1626728 - (CVE-2020-6820) AddressSanitizer: heap-use-after-free /home/fuzzer/firefox/src/dist/include/mozilla/ipc/ProtocolUtils.h:229:31 in Id

https://bugzilla.mozilla.org/show_bug.cgi?id=1626728

Patch Availability(11)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntuxul-ext-lightning (1:68.7.0+build1-0ubuntu0.16.04.2) @ xenial2026-09-19ubuntu
ubuntuxul-ext-lightning (1:68.7.0+build1-0ubuntu0.19.10.1) @ eoan2026-09-19ubuntu
ubuntufirefox-mozsymbols (74.0.1+build1-0ubuntu0.16.04.1) @ xenial2026-09-19ubuntu
redhatthunderbird-0:68.7.0-1.el6_102020-04-16redhat
redhatthunderbird-0:68.7.0-1.el8_12020-04-16redhat
redhatthunderbird-0:68.7.0-1.el8_02020-04-16redhat
redhatthunderbird-0:68.7.0-1.el7_82020-04-16redhat
redhatfirefox-0:68.6.1-1.el6_102020-04-07redhat
redhatfirefox-0:68.6.1-1.el7_82020-04-07redhat
redhatfirefox-0:68.6.1-1.el8_12020-04-07redhat
redhatfirefox-0:68.6.1-1.el8_02020-04-07redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(14 across 7 ecosystems)
Debian:10(2)
PackageVulnerable rangeFixed inDependents
firefox-esr60.7.2esr-1 ... 68.6.1esr-1~deb9u1 (38 versions)68.6.1esr-1~deb10u1—
thunderbird1:60.7.2-1 ... 1:68.7.0-1~deb9u1 (42 versions)1:68.7.0-1~deb10u1—
Debian:11(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—68.6.1esr-1—
thunderbird—1:68.7.0-1—
Debian:12(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—68.6.1esr-1—
thunderbird—1:68.7.0-1—
Debian:13(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—68.6.1esr-1—
thunderbird—1:68.7.0-1—
Debian:14(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—68.6.1esr-1—
thunderbird—1:68.7.0-1—
Debian:8(2)
PackageVulnerable rangeFixed inDependents
firefox-esr45.0.1esr-1 ... 68.6.1esr-1~deb9u1 (186 versions)68.7.0esr-1~deb8u1—
thunderbird1.5-4 ... 1:68.6.0-1~deb9u1 (122 versions)1:68.7.0-1~deb8u1—
Debian:9(2)
PackageVulnerable rangeFixed inDependents
firefox-esr45.9.0esr-1 ... 68.6.0esr-1~deb9u1 (145 versions)68.6.1esr-1~deb9u1—
thunderbird1.5-4 ... 1:68.7.0-1~deb8u1 (123 versions)1:68.7.0-1~deb9u1—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

All Vendor Advisories

(11)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 101× in last 7d / 428× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 1,571 total refreshes for this CVE.

  1. 2026-09-19 19:13 UTCEG score recompute
  2. 2026-09-19 19:13 UTCVendor advisory
  3. 2026-09-19 19:13 UTCGHSA enrichment
  4. 2026-09-19 15:37 UTCEPSS rescore
  5. 2026-09-19 15:14 UTCVendor advisory
  6. 2026-09-19 15:14 UTCGHSA enrichment
  7. 2026-09-19 11:16 UTCVendor advisory
  8. 2026-09-19 11:15 UTCGHSA enrichment
  9. 2026-09-19 07:17 UTCVendor advisory
  10. 2026-09-19 07:17 UTCGHSA enrichment
  11. 2026-09-19 03:19 UTCVendor advisory
  12. 2026-09-19 03:19 UTCGHSA enrichment
  13. 2026-09-18 23:21 UTCVendor advisory
  14. 2026-09-18 23:21 UTCGHSA enrichment
  15. 2026-09-18 19:24 UTCEG score recompute
  16. 2026-09-18 19:24 UTCVendor advisory
  17. 2026-09-18 19:24 UTCGHSA enrichment
  18. 2026-09-18 19:23 UTCEPSS rescore
  19. 2026-09-18 19:20 UTCCISA KEV update
  20. 2026-09-18 15:26 UTCVendor advisory
  21. 2026-09-18 15:26 UTCGHSA enrichment
  22. 2026-09-18 14:15 UTCCISA KEV update
  23. 2026-09-18 11:28 UTCVendor advisory
  24. 2026-09-18 11:28 UTCGHSA enrichment
  25. 2026-09-18 07:29 UTCVendor advisory
Show 75 more
  1. 2026-09-18 07:29 UTCGHSA enrichment
  2. 2026-09-18 03:31 UTCVendor advisory
  3. 2026-09-18 03:31 UTCGHSA enrichment
  4. 2026-09-17 23:33 UTCVendor advisory
  5. 2026-09-17 23:32 UTCGHSA enrichment
  6. 2026-09-17 19:34 UTCEG score recompute
  7. 2026-09-17 19:34 UTCVendor advisory
  8. 2026-09-17 19:34 UTCGHSA enrichment
  9. 2026-09-17 19:22 UTCEPSS rescore
  10. 2026-09-17 15:36 UTCVendor advisory
  11. 2026-09-17 15:36 UTCGHSA enrichment
  12. 2026-09-17 11:37 UTCVendor advisory
  13. 2026-09-17 11:37 UTCGHSA enrichment
  14. 2026-09-17 07:39 UTCVendor advisory
  15. 2026-09-17 07:39 UTCGHSA enrichment
  16. 2026-09-17 03:40 UTCVendor advisory
  17. 2026-09-17 03:40 UTCGHSA enrichment
  18. 2026-09-16 23:42 UTCVendor advisory
  19. 2026-09-16 23:42 UTCGHSA enrichment
  20. 2026-09-16 19:44 UTCVendor advisory
  21. 2026-09-16 19:44 UTCGHSA enrichment
  22. 2026-09-16 15:46 UTCEG score recompute
  23. 2026-09-16 15:46 UTCVendor advisory
  24. 2026-09-16 15:46 UTCGHSA enrichment
  25. 2026-09-16 14:10 UTCCISA KEV update
  26. 2026-09-16 14:04 UTCEPSS rescore
  27. 2026-09-16 11:48 UTCVendor advisory
  28. 2026-09-16 11:48 UTCGHSA enrichment
  29. 2026-09-16 07:50 UTCEG score recompute
  30. 2026-09-16 07:50 UTCVendor advisory
  31. 2026-09-16 07:49 UTCGHSA enrichment
  32. 2026-09-16 03:50 UTCVendor advisory
  33. 2026-09-16 03:50 UTCGHSA enrichment
  34. 2026-09-15 23:52 UTCVendor advisory
  35. 2026-09-15 23:52 UTCGHSA enrichment
  36. 2026-09-15 19:54 UTCVendor advisory
  37. 2026-09-15 19:54 UTCGHSA enrichment
  38. 2026-09-15 15:56 UTCVendor advisory
  39. 2026-09-15 15:56 UTCGHSA enrichment
  40. 2026-09-15 11:58 UTCVendor advisory
  41. 2026-09-15 11:58 UTCGHSA enrichment
  42. 2026-09-15 07:59 UTCVendor advisory
  43. 2026-09-15 07:59 UTCGHSA enrichment
  44. 2026-09-15 04:01 UTCEG score recompute
  45. 2026-09-15 04:01 UTCVendor advisory
  46. 2026-09-15 04:01 UTCGHSA enrichment
  47. 2026-09-15 03:06 UTCEPSS rescore
  48. 2026-09-15 00:02 UTCVendor advisory
  49. 2026-09-15 00:02 UTCGHSA enrichment
  50. 2026-09-14 20:04 UTCVendor advisory
  51. 2026-09-14 20:04 UTCGHSA enrichment
  52. 2026-09-14 19:24 UTCCISA KEV update
  53. 2026-09-14 16:05 UTCVendor advisory
  54. 2026-09-14 16:05 UTCGHSA enrichment
  55. 2026-09-14 12:07 UTCVendor advisory
  56. 2026-09-14 12:07 UTCGHSA enrichment
  57. 2026-09-14 08:09 UTCVendor advisory
  58. 2026-09-14 08:09 UTCGHSA enrichment
  59. 2026-09-14 04:11 UTCVendor advisory
  60. 2026-09-14 04:11 UTCGHSA enrichment
  61. 2026-09-14 00:13 UTCVendor advisory
  62. 2026-09-14 00:13 UTCGHSA enrichment
  63. 2026-09-13 20:15 UTCVendor advisory
  64. 2026-09-13 20:15 UTCGHSA enrichment
  65. 2026-09-13 16:17 UTCVendor advisory
  66. 2026-09-13 16:17 UTCGHSA enrichment
  67. 2026-09-13 12:19 UTCVendor advisory
  68. 2026-09-13 12:19 UTCGHSA enrichment
  69. 2026-09-13 08:21 UTCVendor advisory
  70. 2026-09-13 08:20 UTCGHSA enrichment
  71. 2026-09-13 04:23 UTCVendor advisory
  72. 2026-09-13 04:23 UTCGHSA enrichment
  73. 2026-09-13 00:25 UTCVendor advisory
  74. 2026-09-13 00:25 UTCGHSA enrichment
  75. 2026-09-12 20:27 UTCVendor advisory

Related CVEs(same vendor + same CWE)

Frequently asked(6)

What is CVE-2020-6820?
CVE-2020-6820 is a critical vulnerability published on April 24, 2020. 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.
When was CVE-2020-6820 disclosed?
CVE-2020-6820 was first published in the National Vulnerability Database on April 24, 2020, with the most recent update on November 4, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2020-6820 actively exploited?
Yes. CISA added CVE-2020-6820 to the Known Exploited Vulnerabilities catalog on November 3, 2021, affecting Mozilla Firefox and Thunderbird. KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate patching attention.
What is the CVSS score of CVE-2020-6820?
CVE-2020-6820 has a CVSS v3 base score of 8.1 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.0.
Which products are affected by CVE-2020-6820?
CVE-2020-6820 affects Mozilla Firefox and Thunderbird. The full affected-products list, including version ranges and fixed versions, is shown in the Affected Packages section of this page.
How do I remediate CVE-2020-6820?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2020-6820, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2020-6820

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