Vulnerability report

Exploited in the wild Confirmed confidence In CISA KEV

CVE-2020-6820

Thunderbird

Mozilla / Thunderbird · affected before 68.7.0

Watch CVE-2020-6820 Browse KEV feed
Severity
CVSS 8.1 · High
Confidence
Confirmed
Exploit status
Exploited in the wild
EPSS
7.1%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2020-6820 is an unauthenticated vulnerability affecting Mozilla Thunderbird and 2 other products. Under certain conditions, when handling a ReadableStream, a race condition can cause a use-after-free. We are aware...

Is it exploited?

Yes. Previdian tracks this CVE as a known exploited vulnerability. Confidence is confirmed. Listed in CISA KEV.

Who is affected?

Mozilla / Thunderbird affected before 68.7.0.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

Under certain conditions, when handling a ReadableStream, a race condition can cause a use-after-free

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.

Mozilla Affected
Thunderbird
Before 68.7.0
Mozilla Affected
Firefox
Before 74.0.1
Mozilla Affected
Firefox ESR
Before 68.6.1
View vendor advisory (opens in new tab)
Published
24 Apr 2020
Exploitation Reported
03 Nov 2021
Attack vector
Remote
Complexity
High
Privileges
None
User interaction
None

Tags

cisa

CVE References

Exploitation evidence

Why Previdian marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CISA

Recorded 03 Nov 2021

A trusted third party reported exploitation.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

Learn about Pro API access
Source Added
CISA First 2021-11-03 00:00 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
User-Agents
Callback hosts
0
0
0

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Scanner coverage

No scanner integrations recorded yet.

Virtual patch status

No Previdian virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

No detection artifacts or sensor request patterns are available for this CVE yet.

Check back as sensor telemetry and scanner integrations are updated.

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

8.1 High

Potential damage if exploited. Separate from whether attackers are using it.

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS

7.1%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') CWE-362

All CVSS Scores

CVSS v3.1 8.1 High

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v2.0 6.8 Medium

AV:N/AC:M/Au:N/C:P/I:P/A:P

Timeline

From disclosure to observed exploitation

  1. 00:00 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  2. 15:56 UTC

    CVE published

    Vulnerability disclosed publicly

  3. 00:00 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

Start 14-day Pro trial Read API docs
  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2020-6820

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2020-6820",
  "confidence": "Confirmed",
  "cvss_score": 8.1,
  "cvss_estimated": false,
  "epss_score": 0.07063,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}