Security readout for executives and security teams
Plain-English summary
A flaw in Mozilla’s Push Subscriptions component could undermine separation between websites. The supplied CVSS assessment indicates potentially severe confidentiality, integrity, and availability impact without privileges or user interaction. Mozilla reports fixes in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird 153.2.
Executive priority
Prioritize accelerated patching because the supplied severity is critical and the products are commonly endpoint-facing. Confirm deployment coverage promptly, while avoiding claims of an active campaign because the available evidence does not show exploitation.
Technical view
CVE-2026-84133 is a DOM Push Subscriptions site-isolation issue classified as CWE-346. It has CVSS 3.1 score 9.8 with network reachability, low complexity, no privileges, and no user interaction. The bundle does not disclose the underlying mechanism, affected-version range, or exploit prerequisites beyond that vector.
Likely exposure
Potential exposure exists where Firefox, Firefox ESR, or Thunderbird remains below the stated fixed release for its update channel. The precise vulnerable-version range is not provided, so confirm applicability through Mozilla’s advisories and enterprise software inventory.
Exploitation context
The supplied record does not establish active exploitation, and the CVE is not listed as KEV in the bundle. Public exploit availability and practical attack conditions are also unspecified. Treat the critical CVSS vector as potential severity, not proof of exploitation.
Researcher notes
Public details in the bundle are sparse: the affected-version boundary, root cause, trigger conditions, and practical impact are not described. The listed versions conflict with the description unless interpreted as fixed releases. Researchers should rely on Mozilla’s advisories and Bugzilla record for clarification without assuming exploitability beyond the CVSS vector.
Mitigation direction
- Update Firefox to 155 or the latest supported release.
- Update Firefox ESR to 153.2 or the latest supported ESR release.
- Update Thunderbird to 155, 153.2, or the latest applicable supported release.
- Prioritize managed endpoints unable to receive automatic Mozilla updates.
- Review Mozilla advisories for any channel-specific guidance or revised affected ranges.
Validation and detection
- Inventory installed Firefox, Firefox ESR, and Thunderbird versions across endpoints.
- Confirm each installation meets its applicable fixed release or a newer supported version.
- Verify centralized update policies completed deployment successfully.
- Re-scan endpoints for outdated, portable, or unmanaged installations.
- Monitor Mozilla’s advisories for clarified affected versions and exploitation information.
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-2026-84133 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.
SSVC decision data
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:H3.95.9CISA-ADPVulnerability 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
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://bugzilla.mozilla.org/show_bug.cgi?id=2032388CVE reference, mozilla
- https://www.mozilla.org/security/advisories/mfsa2026-82/CVE reference, mozilla
- https://www.mozilla.org/security/advisories/mfsa2026-85/CVE reference, mozilla
- https://www.mozilla.org/security/advisories/mfsa2026-86/CVE reference, mozilla
- https://www.mozilla.org/security/advisories/mfsa2026-88/CVE reference, mozilla
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.