Security readout for executives and security teams
Plain-English summary
This is a memory-safety flaw in Mozilla Firefox, Firefox ESR, and Thunderbird. Under specific race conditions, the software could use freed memory, which can lead to full confidentiality, integrity, and availability impact. Mozilla reported targeted attacks in the wild, and CISA lists it as known exploited.
Executive priority
Treat this as urgent remediation for any remaining legacy Mozilla deployments. The issue is old, but known exploitation and high impact make unpatched systems unacceptable in managed environments.
Technical view
CVE-2020-6819 is a CWE-416 use-after-free in the nsDocShell destructor caused by a race condition. It affects Thunderbird before 68.7.0, Firefox before 74.0.1, and Firefox ESR before 68.6.1. CVSS 3.1 is 8.1 with high complexity, network attack vector, no privileges, and high CIA impact.
Likely exposure
Exposure is most likely on endpoints or servers still running legacy Mozilla Firefox, Firefox ESR, or Thunderbird versions below the fixed releases. Current managed browser and mail-client fleets should verify version compliance, especially for long-lived ESR installations and unmanaged workstations.
Exploitation context
Mozilla stated it was aware of targeted attacks abusing this flaw. CISA KEV inclusion supports that this vulnerability has been exploited in the wild. The source bundle does not provide exploit mechanics or evidence of broad automated exploitation.
Researcher notes
The public bundle identifies the vulnerable component and affected release thresholds but does not include safe reproduction details. Focus validation on version evidence, package provenance, and whether compensating controls cover unmanaged browsers or mail clients.
Mitigation direction
- Upgrade Firefox to 74.0.1 or later.
- Upgrade Firefox ESR to 68.6.1 or later.
- Upgrade Thunderbird to 68.7.0 or later.
- Check Mozilla and OS vendor advisories for supported package guidance.
- Prioritize unmanaged endpoints and legacy ESR deployments.
Validation and detection
- Inventory installed Firefox, Firefox ESR, and Thunderbird versions.
- Confirm no affected versions remain below the fixed releases.
- Review endpoint management coverage for unmanaged or stale devices.
- Check vulnerability scanner results against CVE-2020-6819.
- Validate Linux package versions against OS vendor advisories.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-416: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2020-6819 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.1 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CISA KEV status
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H2.25.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.1HighVector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://www.mozilla.org/security/advisories/mfsa2020-14/CVE reference · x_refsource_MISC
- https://www.mozilla.org/security/advisories/mfsa2020-11/CVE reference · x_refsource_MISC
- https://bugzilla.mozilla.org/show_bug.cgi?id=1620818CVE reference · x_refsource_MISC
- USN-4335-1CVE reference · vendor-advisory, x_refsource_UBUNTU
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-6819CVE reference · government-resource
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.