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CVE Record

CVE-2026-4696: Use-after-free in the Layout: Text and Fonts component

Use-after-free in the Layout: Text and Fonts component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

CVE-2026-4696 is a critical memory safety flaw in Mozilla’s text and font layout handling. A successful attack could compromise confidentiality, integrity, and availability. Mozilla says it is fixed in Firefox 149, Firefox ESR 115.34 and 140.9, Thunderbird 149, and Thunderbird 140.9.

Executive priority

Treat as urgent patching for browsers and mail clients. There is no supplied evidence of active exploitation, but the critical score and memory safety impact justify rapid fleet-wide remediation and exception tracking.

Technical view

The issue is a use-after-free in Layout: Text and Fonts, mapped to CWE-416 and CWE-825. The supplied CVSS 3.1 score is 9.8 with network attack vector, low complexity, no privileges, and no user interaction. The bundle does not provide trigger details or proof-of-concept information.

Likely exposure

Organizations are exposed where Firefox, Firefox ESR, or Thunderbird remain below the fixed releases named by Mozilla, or where Red Hat-packaged Mozilla components have not received the relevant RHSA updates. ESR deployments and managed desktop fleets are the main inventory focus.

Exploitation context

The source bundle does not show CISA KEV listing or any cited evidence of active exploitation. Risk remains high because use-after-free flaws in browser or mail-client rendering components can be severe, but exploitation claims should not be made from this evidence alone.

Researcher notes

Public details in the bundle are limited to vulnerability class, component, fixed versions, CVSS, CWE mappings, and vendor references. Avoid assuming exploit primitives or affected code paths beyond Layout: Text and Fonts unless vendor bug details become available.

Mitigation direction

  • Upgrade Firefox to 149 or the applicable fixed ESR release.
  • Upgrade Thunderbird to 149 or Thunderbird 140.9 where applicable.
  • Apply relevant Red Hat RHSA updates for packaged Mozilla components.
  • Prioritize managed endpoints, VDI images, and ESR channels.
  • Check Mozilla and Red Hat advisories for platform-specific guidance.

Validation and detection

  • Inventory Firefox, Firefox ESR, and Thunderbird versions across endpoints.
  • Confirm fixed versions are installed after patch deployment.
  • Review Red Hat advisory applicability for Linux fleets.
  • Verify package manager update status on managed systems.
  • Track exceptions for unsupported or pinned browser versions.
Prepared
Confidence
high
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-416: 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
cwe · low confidence lookup

CWE-825: 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
cve · low confidence lookup

CVE-2026-4696 mapping review

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

Open ATT&CK lookup
Vulnerability profileCVE Program record
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

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: yesTechnical 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
9.8CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H3.95.9CISA-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

9.8Critical
CVSS 3.1 vector shape for CVE-2026-4696Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/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: Use-after-free in the Layout: Text and Fonts component
other:Red Hat severity ratingcvssV3_1
  • 2026-03-24T13:03:00.059Z: Reported to Red Hat.
  • 2026-03-24T12:30:26.919Z: 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-416CWE-825

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

CWE-416 · source CWE mapping

Use After Free

Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-825 · source CWE mapping

Expired Pointer Dereference

Expired Pointer Dereference represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs