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CVE Record

CVE-2026-4692: Sandbox escape in the Responsive Design Mode component

Sandbox escape in the Responsive Design Mode component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

CriticalCVSS 9.6Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

CVE-2026-4692 is a critical Mozilla sandbox escape tied to the Responsive Design Mode component. If triggered, it could let attacker-controlled content break out of expected browser isolation. Mozilla says it is fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

Executive priority

Prioritize remediation this cycle, especially on managed browsers, mail clients, and developer workstations. No active exploitation is shown in the bundle, but the critical score and sandbox-escape impact justify expedited patching.

Technical view

The CVSS 3.1 score is 9.6 with network attack vector, low complexity, no privileges, required user interaction, changed scope, and high confidentiality, integrity, and availability impact. The listed weakness is CWE-653. The source bundle does not provide technical root cause details or safe proof-of-concept information.

Likely exposure

Exposure is most likely on endpoints running Mozilla Firefox, Firefox ESR, or Thunderbird below the fixed releases cited by Mozilla. Red Hat advisories indicate downstream Linux packages may also require updates. The bundle does not identify other affected products.

Exploitation context

The CVSS vector indicates remote attackability with user interaction required. The provided data says KEV is false, and no cited source in the bundle states active exploitation. Treat this as urgent because sandbox escapes can weaken a key browser containment boundary.

Researcher notes

Public detail is limited in the provided bundle. The issue is described only as a Responsive Design Mode sandbox escape with CWE-653. Avoid assuming exploit mechanics, affected configurations, or bypass details beyond the CVSS vector and Mozilla fixed-version statements.

Mitigation direction

  • Update Firefox to 149, ESR 115.34, ESR 140.9, or later fixed releases.
  • Update Thunderbird to 149, 140.9, or later fixed releases.
  • Apply applicable Red Hat security advisories for managed Linux fleets.
  • Check Mozilla and operating-system vendor guidance for platform-specific packages.
  • Prioritize developer and high-risk user workstations using Firefox or Thunderbird.

Validation and detection

  • Inventory Firefox, Firefox ESR, and Thunderbird versions across endpoints.
  • Confirm update deployment reached the fixed versions listed by Mozilla.
  • Check Red Hat errata applicability for subscribed Linux systems.
  • Review vulnerability scanner findings against actual installed package versions.
  • Monitor Mozilla advisories and CISA KEV for exploitation status changes.
Prepared
Confidence
medium
Sources
11

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-653: 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 lookup
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.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-4692 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
9.6 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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.

2CVSS vectors
5Timeline events
2ADP providers
35Source links

SSVC decision data

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

CVSS vector scores

2 official scores

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
9.6CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H2.86CISA-ADP
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H1.65.9redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

9.6Critical
CVSS 3.1 vector shape for CVE-2026-4692Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

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

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
redhat-SADPfirefox: thunderbird: Sandbox escape in the Responsive Design Mode component
other:Red Hat severity ratingcvssV3_1
  • 2026-03-24T13:03:24.423Z: Reported to Red Hat.
  • 2026-03-24T12:30:24.864Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MozillaFirefox115.34, 140.9, 149Listed
MozillaThunderbird140.9, 149Listed
Weakness

CWE details

CWE-653

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