Security readout for executives and security teams
Plain-English summary
CVE-2026-2790 is a Mozilla same-origin policy bypass in the Networking: JAR component. In practical terms, Firefox or Thunderbird could incorrectly allow content to cross browser security boundaries after user interaction. Mozilla fixed it in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.
Executive priority
Treat as a high-priority endpoint patching item. The issue affects common user-facing software and has high potential impact, but current supplied evidence does not show active exploitation.
Technical view
The issue is classified as CWE-346 and rated CVSS 8.8. The vector is network-exploitable, low complexity, no privileges required, with user interaction required. Reported impacts are high confidentiality, integrity, and availability. Public sources identify fixes but do not provide safe operational detail on exploitation mechanics.
Likely exposure
Organizations using Mozilla Firefox, Firefox ESR, Thunderbird, or Thunderbird ESR below the fixed releases may be exposed. Exposure is highest on endpoints where users browse untrusted content or open externally supplied content in Thunderbird.
Exploitation context
The CVE record does not indicate CISA KEV listing, and the supplied sources do not state active exploitation. Exploitation requires user interaction, so phishing or malicious web-content scenarios are plausible, but specific techniques are not publicly substantiated in the provided sources.
Researcher notes
Public detail is limited to a same-origin policy bypass in Networking: JAR. Focus validation on version exposure and advisory alignment. Avoid assuming exploitability beyond the CVSS vector and Mozilla’s stated impact until more technical detail is public.
Mitigation direction
- Update Firefox to 148 or later where applicable.
- Update Firefox ESR to 140.8 or later.
- Update Thunderbird to 148 or later where applicable.
- Update Thunderbird ESR to 140.8 or later.
- Check Mozilla advisories for any platform-specific guidance.
Validation and detection
- Inventory Firefox and Thunderbird versions across managed endpoints.
- Confirm ESR deployments are at 140.8 or later.
- Confirm rapid-release deployments are at 148 or later.
- Review Mozilla advisory pages for this CVE.
- Monitor EDR and proxy telemetry for suspicious browser-driven activity.
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-346: 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-2026-2790 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
- 8.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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:R/S:U/C:H/I:H/A:H2.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.8HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://bugzilla.mozilla.org/show_bug.cgi?id=2008426CVE reference
- https://www.mozilla.org/security/advisories/mfsa2026-13/CVE reference
- https://www.mozilla.org/security/advisories/mfsa2026-15/CVE reference
- https://www.mozilla.org/security/advisories/mfsa2026-16/CVE reference
- https://www.mozilla.org/security/advisories/mfsa2026-17/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.
Origin Validation Error
Origin Validation Error represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.