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: 6%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
6%
EPSS %ILE
93%
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+build1-0ubuntu0.19.10.1) @ eoan2026-07-26ubuntu
ubuntuxul-ext-lightning (1:68.7.0+build1-0ubuntu0.16.04.2) @ xenial2026-07-26ubuntu
ubuntufirefox-mozsymbols (74.0.1+build1-0ubuntu0.16.04.1) @ xenial2026-07-26ubuntu
redhatthunderbird-0:68.7.0-1.el8_02020-04-16redhat
redhatthunderbird-0:68.7.0-1.el7_82020-04-16redhat
redhatthunderbird-0:68.7.0-1.el6_102020-04-16redhat
redhatthunderbird-0:68.7.0-1.el8_12020-04-16redhat
redhatfirefox-0:68.6.1-1.el8_02020-04-07redhat
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

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.

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 66× in last 7d / 396× 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 800 total refreshes for this CVE.

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

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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.

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