Security readout for executives and security teams
Plain-English summary
CVE-2026-4702 is a critical Mozilla JavaScript engine flaw involving JIT miscompilation. Mozilla states it is fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9. Organizations with unmanaged or delayed browser and mail-client updates should treat this as urgent because the CVSS rating indicates potential full confidentiality, integrity, and availability impact.
Executive priority
Prioritize remediation in the next browser and email-client patch window, preferably immediately for high-risk users. The issue is critical by CVSS and affects common endpoint software, but current public sources do not confirm active exploitation.
Technical view
The CVE describes JIT miscompilation in Mozilla’s JavaScript Engine component, mapped to CWE-843. The published CVSS 3.1 score is 9.8 with network attack vector, low complexity, no privileges, and high impact across confidentiality, integrity, and availability. Public sources do not provide safe operational detail on the exact trigger or exploit mechanics.
Likely exposure
Exposure is most likely on endpoints running Firefox, Firefox ESR, Thunderbird, or Thunderbird ESR that have not been updated to the fixed releases named by Mozilla. Internet-facing browsing and email workflows increase practical risk, but the sources do not identify specific platforms or configurations beyond the Mozilla products.
Exploitation context
The source bundle marks CISA KEV as false, and no cited source states active exploitation. The vulnerability is still high priority because it is remotely reachable per CVSS, requires low attack complexity, and affects widely deployed client software processing web or message content.
Researcher notes
Public detail is limited to JIT miscompilation, JavaScript Engine, CWE-843, and Mozilla fixed releases. Avoid assuming exploitability characteristics beyond the CVSS vector and advisories. Bugzilla and Mozilla security advisories are the primary references for any future technical clarification.
Mitigation direction
- Update Firefox to version 149 or a later fixed release.
- Update Firefox ESR to version 140.9 or a later fixed ESR release.
- Update Thunderbird to version 149 or a later fixed release.
- Update Thunderbird ESR to version 140.9 or a later fixed ESR release.
- Review Mozilla advisories for deployment-specific guidance and release notes.
Validation and detection
- Inventory Firefox and Thunderbird versions across managed endpoints.
- Confirm ESR installations are on 140.9 or later fixed ESR builds.
- Confirm standard-channel installations are on 149 or later fixed builds.
- Check software management tools for failed or pending Mozilla updates.
- Monitor Mozilla advisories for any revised affected-version guidance.
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-843: 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-2026-4702 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
- Critical
- CVSS
- 9.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/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.
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:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
9.8CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://bugzilla.mozilla.org/show_bug.cgi?id=2013560CVE reference
- https://www.mozilla.org/security/advisories/mfsa2026-20/CVE reference
- https://www.mozilla.org/security/advisories/mfsa2026-22/CVE reference
- https://www.mozilla.org/security/advisories/mfsa2026-23/CVE reference
- https://www.mozilla.org/security/advisories/mfsa2026-24/CVE reference
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.
Access of Resource Using Incompatible Type ('Type Confusion')
Access of Resource Using Incompatible Type ('Type Confusion') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.