CASCACascade Atlas

Evidence dossier

CVE-2020-6820

CVE-2020-6820

62.0–80.3Priority evidence range
As known Jul 19, 2026, 5:00 AM UTCgen-56ccdaf9

Normalized restatement

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.

State
PUBLISHED
Published
Apr 24, 2020
Updated
Oct 21, 2025
Evidence coverage
72%
CISA KEVCatalog member

Apply updates per vendor instructions.

FIRST EPSS6.30%

2026-07-18 · v2026.06.15 · percentile 92.8%

Source stateConflict visible

Distinct CVSS assessments remain side by side; none are averaged.

Source comparison

Who said what

CISA-ADPindependent enrichment
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CISA ADP Vulnrichment

CVEderivative copy
container

CVE Program Container

mozillaoriginal assertion
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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.

CISA KEVoriginal assertion
observed_exploitation

Mozilla Firefox And Thunderbird Use-After-Free Vulnerability

FIRST EPSSoriginal assertion
model_probability

Probability 0.063050000000; percentile 0.928230000000

Applicability

Cited product scope

Trace impact →
MozillaFirefox
[{"status": "affected", "version": "unspecified", "lessThan": "74.0.1", "versionType": "custom"}]unknown
MozillaFirefox ESR
[{"status": "affected", "version": "unspecified", "lessThan": "68.6.1", "versionType": "custom"}]unknown
MozillaThunderbird
[{"status": "affected", "version": "unspecified", "lessThan": "68.7.0", "versionType": "custom"}]unknown
Unknown vendorUnknown product
cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*; end excluding 74.0.1supported
Unknown vendorUnknown product
cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*; end excluding 68.6.1supported
Unknown vendorUnknown product
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*; end excluding 68.7.0supported

Assessments

CVSS by origin

8.1
nvd@nist.govCVSS 3.1 · role PrimaryCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
6.8
nvd@nist.govCVSS 2.0 · role PrimaryAV:N/AC:M/Au:N/C:P/I:P/A:P
8.1
134c704f-9b21-4f2e-91b3-4a467353bcc0CVSS 3.1 · role SecondaryCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
8.1
CISA-ADPCVSS 3.1 · role unknownCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Limitations and unknowns

  • KEV membership is authoritative for the catalog, not proof of exposure in any environment.
  • EPSS is a dated model probability and not an individual-environment prediction.
  • Affected or fixed status applies only to the exact cited product and version scope; unresolved scope remains unknown.
  • NVD-carried upstream facts remain derivative and are not independent corroboration.
  • Only NVD metrics validated under the generation-bound calculator are Public Priority eligible; direct CVE record metrics remain display-only.
  • NVD CVSS source eligibility is closed: NVD-authored, exact record-source, or registered same-CVE container origin; unmapped sources remain display-only.
  • Factor D is unknown in Public Core because no accepted canonical mapping-obligation ledger is present.
  • Core replay supports the active and immediately prior generation; retrospective valid-at replay is deferred.