Security readout for executives and security teams
Plain-English summary
A flaw can bypass a security protection in Mozilla’s JavaScript garbage-collection component. The supplied CVSS 9.1 rating indicates remote, low-complexity attack potential without privileges or user interaction, with high confidentiality and integrity impact. Mozilla reports fixes in current Firefox and Thunderbird releases, making rapid client updates prudent.
Executive priority
Treat this as an urgent endpoint patching issue because the supplied severity is critical and potential confidentiality and integrity impact is high. Accelerate Firefox and Thunderbird updates, verify deployment success, and report remaining outdated installations. There is no supplied evidence of active exploitation, but incomplete disclosure increases uncertainty rather than reducing potential risk.
Technical view
CVE-2026-74938 is classified as CWE-693, indicating a protection-mechanism failure in JavaScript garbage collection. Its CVSS vector is AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. The bundle does not identify the bypassed mitigation, root cause, precise vulnerable version ranges, delivery path, or whether code execution is possible.
Likely exposure
Exposure is most likely on endpoints running Firefox or Thunderbird releases older than the stated fixed versions. The supplied affected-version data conflicts with the description by listing versions described elsewhere as fixed. Exact vulnerable lower bounds are therefore unknown, so inventories should be compared against Mozilla’s advisories and supported release channels.
Exploitation context
The supplied evidence does not support active exploitation. The CVE is not marked as KEV-listed, and the bundle cites no in-the-wild exploitation or public proof of concept. The critical score represents potential exploitability and impact, not confirmed attacks. Limited technical disclosure prevents assessment of practical reliability or attack delivery.
Researcher notes
The record describes a mitigation bypass in JavaScript GC but provides no mechanism, trigger, patch diff, or attack-chain detail. The structured affected list includes 153.1 and 154, while the description explicitly calls those fixed versions. Do not treat those releases as vulnerable without clarification. Exact pre-fix ranges and exploitability remain unresolved.
Mitigation direction
- Update Firefox to version 154 and Firefox ESR to 153.1 or later.
- Update Thunderbird to version 154 or Thunderbird 153.1 or later.
- Check Mozilla advisories for channel-specific guidance and any subsequently published mitigations.
- Prioritize unmanaged, internet-facing, and high-value user endpoints during rollout.
Validation and detection
- Inventory Firefox and Thunderbird versions across managed and unmanaged endpoints.
- Confirm installed versions meet or exceed Mozilla’s stated fixed releases.
- Review endpoint-management records for failed, deferred, or incomplete updates.
- Recheck Mozilla advisories for clarified vulnerable ranges and 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-693: 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-2026-74938 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:H/A:N
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:N3.95.2CISA-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:H/A:N
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=2053688CVE 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.
Protection Mechanism Failure
Protection Mechanism Failure represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.