Security readout for executives and security teams
Plain-English summary
CVE-2026-4723 is a critical Mozilla vulnerability in the JavaScript engine, fixed in Firefox 149 and Thunderbird 149. The issue is a use-after-free memory safety bug that can affect confidentiality, integrity, and availability. No provided source shows active exploitation, but the severity and network-exploitable CVSS profile make timely update validation important.
Executive priority
Treat as urgent patch validation for Mozilla browser and email-client fleets. There is no sourced evidence of active exploitation, but the critical CVSS score and memory-safety impact justify prompt action, especially on internet-facing user workstations.
Technical view
Mozilla describes a CWE-416 use-after-free in the JavaScript Engine component. The CVSS 3.1 score is 9.8 with network attack vector, low complexity, no privileges, and no user interaction. The source bundle says it was fixed in Firefox 149 and Thunderbird 149; exact vulnerable version ranges are not clearly stated in the provided data.
Likely exposure
Organizations using Mozilla Firefox or Thunderbird should check whether deployments are updated to version 149 or later. The provided sources do not clearly define the vulnerable version range, so exposure assessment should rely on Mozilla advisory details and local version inventory.
Exploitation context
No CISA KEV listing or provided source indicates active exploitation. CVSS indicates potential remote, low-complexity exploitation without privileges or user interaction, but the bundle does not provide exploit details or confirmation of weaponization.
Researcher notes
The record identifies CWE-416 in the JavaScript engine and references a Mozilla Bugzilla entry plus two advisories. The provided data is limited and internally ambiguous on affected versions versus fixed versions. Avoid assuming exploit availability or vulnerable ranges beyond Mozilla’s published guidance.
Mitigation direction
- Update Firefox to version 149 or later.
- Update Thunderbird to version 149 or later.
- Review Mozilla advisories MFSA 2026-20 and MFSA 2026-23.
- Prioritize managed endpoints with browser or email-client exposure.
- Check vendor guidance if version applicability is unclear.
Validation and detection
- Inventory installed Firefox and Thunderbird versions.
- Confirm Firefox is at least version 149.
- Confirm Thunderbird is at least version 149.
- Map unmanaged endpoints using Mozilla products.
- Monitor Mozilla advisories for clarifications or follow-up fixes.
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-2026-4723 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=2013573CVE reference
- https://www.mozilla.org/security/advisories/mfsa2026-20/CVE reference
- https://www.mozilla.org/security/advisories/mfsa2026-23/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.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.