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CVE Record

CVE-2026-75874: Sandbox escape in the Remote Settings Client component

Sandbox escape in the Remote Settings Client component. This vulnerability was fixed in Firefox 154, Thunderbird 154, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 140.15, and Thunderbird 153.2.

CriticalCVSS 10Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

A flaw in Mozilla’s Remote Settings Client could let an attacker break out of a security sandbox and compromise confidentiality, integrity, and availability. Mozilla identifies fixed releases for Firefox and Thunderbird. The supplied evidence does not define every vulnerable earlier version, so organizations should inventory installations and apply the appropriate fixed release promptly.

Executive priority

Treat as an urgent patching priority because the stated maximum CVSS score, sandbox escape, and broad impact could enable serious endpoint compromise. Accelerate browser and mail-client updates, but avoid claiming an active emergency campaign: the supplied sources do not establish exploitation in the wild.

Technical view

CVE-2026-75874 is a sandbox escape in Mozilla’s Remote Settings Client component, classified as CWE-693. The supplied CVSS 3.1 vector scores 10.0 and describes network-reachable, low-complexity exploitation requiring neither privileges nor user interaction, with changed scope and high impacts. The bundle does not provide root-cause details or complete vulnerable-version boundaries.

Likely exposure

Potential exposure exists wherever Firefox or Thunderbird remains below the applicable fixed release. Fixed versions are Firefox 154, ESR 115.40, ESR 140.15, ESR 153.2; and Thunderbird 154, 140.15, 153.2. Confirm affected-version boundaries with Mozilla because the supplied bundle does not enumerate them completely.

Exploitation context

The CVSS vector indicates a potentially remote, unauthenticated, low-complexity path without user interaction. However, the bundle marks this CVE as absent from KEV and provides no cited evidence of active exploitation, public proof-of-concept availability, or attack campaigns. Treat exploitation status as unconfirmed rather than assuming the issue is unused.

Researcher notes

Publicly supplied details identify the affected component and sandbox-escape outcome but omit root cause, prerequisites beyond CVSS, vulnerable-version ranges, and exploit mechanics. The unusual version list in the affected data matches versions explicitly described as fixed; do not interpret those releases as vulnerable without additional Mozilla evidence.

Mitigation direction

  • Update Firefox to 154 or the applicable fixed ESR release.
  • Update Thunderbird to 154, 140.15, or 153.2, as applicable.
  • Prioritize internet-connected endpoints and systems handling sensitive communications.
  • Check Mozilla advisories for deployment-specific guidance and affected-version boundaries.

Validation and detection

  • Inventory installed Firefox and Thunderbird versions across managed endpoints.
  • Verify versions meet or exceed the applicable Mozilla fixed release.
  • Confirm update deployment succeeded, including inactive and intermittently connected devices.
  • Review endpoint telemetry for unusual browser or mail-client child processes and post-sandbox activity.
Prepared
Confidence
medium
Sources
10

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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 · low confidence lookup

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.

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description · low confidence lookup

Privilege behavior lookup

The CVE wording references privilege impact, so privilege escalation and authorization behavior review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

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cve · low confidence lookup

CVE-2026-75874 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Critical
CVSS
10 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Official CVE source material

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.

1CVSS vectors
3Timeline events
1ADP providers
9Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: total

CVSS vector scores

1 official score

We 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.

ScoreVersionSeverityVectorExploitImpactSource
10CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H3.96CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

10Critical
CVSS 3.1 vector shape for CVE-2026-75874Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MozillaFirefox115.40, 140.15, 153.2, 154Listed
MozillaThunderbird140.15, 153.2, 154Listed
Weakness

CWE details

CWE-693

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-693 · source CWE mapping

Protection Mechanism Failure

Protection Mechanism Failure represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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