CVE-2020-12387

HIGHNVD 8.18.1—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 8.1 under NVD CVSS v3. EPSS exploit probability: 1.4%, top 30% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
8.1EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 8.1Exploit: None knownExposed: 0

A fix is available — apply it.

A race condition when running shutdown code for Web Worker led to a use-after-free vulnerability. This resulted in a potentially exploitable crash. This vulnerability affects Firefox ESR < 68.8, Firefox < 76, and Thunderbird < 68.8.0.

CVSS v3
8.1
EG Score
8.1(medium)
EG Risk
42(Track)
EG Risk 42/100SSVC: Track

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
Severity81% × 45%
Exploitation1% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
1%
EPSS %ILE
71%
KEV
Not listed

Published

May 26, 2020

Last Modified

November 21, 2024

Advisory Details (6)

Auto-updated Sep 9, 2026
No patch confirmed yet.
generic

Mozilla Firefox: Multiple vulnerabilities (GLSA 202005-04) — Gentoo security

https://security.gentoo.org/glsa/202005-04
generic

Mozilla Thunderbird: Multiple vulnerabilities (GLSA 202005-03) — Gentoo security

https://security.gentoo.org/glsa/202005-03
generic

1545345 - (CVE-2020-12387) Web Workers - Use After Free with XMLHttpRequest

https://bugzilla.mozilla.org/show_bug.cgi?id=1545345
generic

Security Vulnerabilities fixed in Thunderbird 68.8.0 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2020-18/
generic

Security Vulnerabilities fixed in Firefox ESR 68.8 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2020-17/
generic

Security Vulnerabilities fixed in Firefox 76 — Mozilla

https://www.mozilla.org/security/advisories/mfsa2020-16/

Patch Availability(12)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntufirefox-mozsymbols (76.0+build2-0ubuntu0.16.04.1) @ xenial2026-05-27ubuntu
ubuntuxul-ext-lightning (1:68.8.0+build2-0ubuntu0.16.04.2) @ xenial2026-05-27ubuntu
redhatthunderbird-0:68.8.0-1.el7_82020-05-11redhat
redhatthunderbird-0:68.8.0-1.el6_102020-05-11redhat
redhatthunderbird-0:68.8.0-1.el8_22020-05-11redhat
redhatthunderbird-0:68.8.0-1.el8_02020-05-11redhat
redhatthunderbird-0:68.8.0-1.el8_12020-05-11redhat
redhatfirefox-0:68.8.0-1.el6_102020-05-06redhat
redhatfirefox-0:68.8.0-1.el7_82020-05-06redhat
redhatfirefox-0:68.8.0-1.el8_22020-05-06redhat
redhatfirefox-0:68.8.0-1.el8_02020-05-06redhat
redhatfirefox-0:68.8.0-1.el8_12020-05-06redhat

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 ... 68.8.0esr-1~deb9u1 (46 versions)68.8.0esr-1~deb10u1—
thunderbird1:60.7.2-1 ... 1:68.8.0-1~deb9u1 (46 versions)1:68.8.0-1~deb10u1—
Debian:11(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—68.8.0esr-1—
thunderbird—1:68.8.0-1—
Debian:12(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—68.8.0esr-1—
thunderbird—1:68.8.0-1—
Debian:13(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—68.8.0esr-1—
thunderbird—1:68.8.0-1—
Debian:14(2)
PackageVulnerable rangeFixed inDependents
firefox-esr—68.8.0esr-1—
thunderbird—1:68.8.0-1—
Debian:8(2)
PackageVulnerable rangeFixed inDependents
firefox-esr45.0.1esr-1 ... 68.7.0esr-1~deb9u1 (190 versions)68.8.0esr-1~deb8u1—
thunderbird1.5-4 ... 1:68.7.0-1~deb9u1 (126 versions)1:68.8.0-1~deb8u1—
Debian:9(2)
PackageVulnerable rangeFixed inDependents
firefox-esr45.9.0esr-1 ... 68.8.0esr-1~deb8u1 (153 versions)68.8.0esr-1~deb9u1—
thunderbird1.5-4 ... 1:68.8.0-1~deb8u1 (127 versions)1:68.8.0-1~deb9u1—

Weakness Classification(2)

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

All Vendor Advisories

(12)

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 7× in last 7d / 24× 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 149 total refreshes for this CVE.

  1. 2026-09-19 15:37 UTCEPSS rescore
  2. 2026-09-18 19:23 UTCEPSS rescore
  3. 2026-09-17 19:22 UTCEPSS rescore
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  12. 2026-09-07 11:48 UTCOSV refresh
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  25. 2026-08-20 22:51 UTCEPSS rescore
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  1. 2026-08-20 21:01 UTCOSV refresh
  2. 2026-08-19 17:00 UTCEPSS rescore
  3. 2026-08-18 13:44 UTCEPSS rescore
  4. 2026-08-17 13:43 UTCEPSS rescore
  5. 2026-08-16 14:52 UTCEPSS rescore
  6. 2026-08-16 02:11 UTCEPSS rescore
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  8. 2026-08-13 21:57 UTCEPSS rescore
  9. 2026-08-12 13:47 UTCEPSS rescore
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  11. 2026-08-08 16:33 UTCEPSS rescore
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  13. 2026-08-06 13:43 UTCEPSS rescore
  14. 2026-08-05 19:14 UTCEPSS rescore
  15. 2026-08-05 13:10 UTCOSV refresh
  16. 2026-08-04 15:06 UTCEPSS rescore
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  21. 2026-07-30 16:24 UTCEPSS rescore
  22. 2026-07-30 01:27 UTCEPSS rescore
  23. 2026-07-28 15:32 UTCEPSS rescore
  24. 2026-07-26 14:51 UTCEPSS rescore
  25. 2026-07-25 14:14 UTCEPSS rescore
  26. 2026-07-24 14:14 UTCEPSS rescore
  27. 2026-07-23 14:15 UTCEPSS rescore
  28. 2026-07-23 14:15 UTCEPSS rescore
  29. 2026-07-23 01:48 UTCEG score recompute
  30. 2026-07-22 22:33 UTCEG score recompute
  31. 2026-07-22 14:05 UTCEPSS rescore
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  35. 2026-07-19 14:28 UTCEPSS rescore
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  37. 2026-07-19 11:52 UTCOSV refresh
  38. 2026-07-19 02:26 UTCEPSS rescore
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  40. 2026-07-18 10:02 UTCEPSS rescore
  41. 2026-07-16 16:59 UTCEPSS rescore
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  48. 2026-07-11 08:24 UTCEPSS rescore
  49. 2026-07-09 19:06 UTCEPSS rescore
  50. 2026-07-08 15:11 UTCEPSS rescore
  51. 2026-07-07 13:43 UTCEPSS rescore
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  57. 2026-07-01 20:31 UTCOSV refresh
  58. 2026-07-01 15:03 UTCEPSS rescore
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  65. 2026-06-27 03:06 UTCEPSS rescore
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  68. 2026-06-24 14:03 UTCEPSS rescore
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  70. 2026-06-23 21:31 UTCEPSS rescore
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  74. 2026-06-21 14:54 UTCEPSS rescore
  75. 2026-06-21 14:54 UTCEPSS rescore

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2020-12387?
CVE-2020-12387 is a high vulnerability published on May 26, 2020. A race condition when running shutdown code for Web Worker led to a use-after-free vulnerability. This resulted in a potentially exploitable crash. This vulnerability affects Firefox ESR < 68.8, Firefox < 76, and Thunderbird < 68.8.0.
When was CVE-2020-12387 disclosed?
CVE-2020-12387 was first published in the National Vulnerability Database on May 26, 2020, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2020-12387 actively exploited?
CVE-2020-12387 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1% probability of exploitation in the next 30 days, which ranks it in the top 28.7% of all scored CVEs.
What is the CVSS score of CVE-2020-12387?
CVE-2020-12387 has a CVSS v3 base score of 8.1 (NVD).
How do I remediate CVE-2020-12387?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2020-12387, 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

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