Security readout for executives and security teams
Plain-English summary
A flaw in Mozilla’s CSS processing can undermine site isolation, potentially exposing sensitive information or disrupting the application. The supplied CVSS assessment indicates remote reachability without privileges or user interaction, high confidentiality and availability impact, and no integrity impact.
Executive priority
Treat this as an expedited browser and email-client update because exposure may affect confidentiality and availability remotely. Confirm coverage promptly, while avoiding claims of an active campaign without supporting evidence.
Technical view
CVE-2026-74986 affects the CSS Parsing and Computation component. It is classified as CWE-200 with CVSS 3.1 score 9.1: network-accessible, low complexity, no privileges or user interaction, unchanged scope, high confidentiality and availability impact, and no integrity impact.
Likely exposure
Prioritize managed and unmanaged installations of Firefox and Thunderbird that do not contain the fixes released in Firefox 154, Firefox ESR 153.1, Thunderbird 154, or Thunderbird 153.1. The bundle does not identify affected operating systems, deployment configurations, or earlier version boundaries.
Exploitation context
The supplied record is not listed in KEV, and the source bundle provides no evidence of active exploitation or a public exploit. Critical severity reflects technical impact and reachability, not confirmed attacks.
Researcher notes
The bundle’s affected entries list versions 153.1 and 154, while its description identifies those releases as fixed. Validate precise affected ranges against Mozilla’s advisories. The provided summary does not explain the isolation failure mechanism, affected platforms, indicators, or exploitability constraints beyond the CVSS vector.
Mitigation direction
- Upgrade Firefox to version 154 or a later vendor-supported release.
- Upgrade Firefox ESR to version 153.1 or a later vendor-supported release.
- Upgrade Thunderbird to version 154, 153.1, or a later applicable vendor-supported release.
- Consult the applicable Mozilla advisory for channel-specific guidance and deployment details.
Validation and detection
- Inventory Firefox and Thunderbird versions across managed and unmanaged endpoints.
- Confirm installed release channels contain the Mozilla fixes identified for this CVE.
- Check endpoint management reports for failed updates and devices missing recent check-ins.
- Review Mozilla advisories and Bugzilla for clarified affected-version boundaries or additional 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-200: Information exposure and cloud metadata lookup
Information exposure and SSRF weaknesses can make discovery, cloud metadata, and credential material review relevant. 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-2026-74986 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
- 9.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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:N/A:H3.95.2CISA-ADPVulnerability scoring details
Base CVSS 3.1 score
9.1CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/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=2060048CVE reference, mozilla
- https://www.mozilla.org/security/advisories/mfsa2026-74/CVE reference, mozilla
- https://www.mozilla.org/security/advisories/mfsa2026-77/CVE reference, mozilla
- https://www.mozilla.org/security/advisories/mfsa2026-78/CVE reference, mozilla
- https://www.mozilla.org/security/advisories/mfsa2026-80/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.
Exposure of Sensitive Information to an Unauthorized Actor
Exposure of Sensitive Information to an Unauthorized Actor represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.