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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. Mozilla says it is fixed in Firefox 149, Firefox ESR 115.34/140.9, Thunderbird 149, and Thunderbird 140.9. The CVSS score is 9.8, so unpatched browser and mail-client installations should be treated as urgent exposure.

Executive priority

Prioritize patching in the next emergency browser and mail-client maintenance cycle. The available evidence does not prove exploitation, but the critical score and memory-safety class justify fast remediation on endpoints and Linux fleets.

Technical view

The issue is a use-after-free in the Layout: Text and Fonts component, mapped to CWE-416 and CWE-825. The published CVSS vector is AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H, indicating high confidentiality, integrity, and availability impact. Source data does not include exploit mechanics.

Likely exposure

Exposure is likely where Firefox, Firefox ESR, or Thunderbird installations have not been updated to the Mozilla fixed releases. Red Hat references indicate downstream Linux packages may also require vendor errata review and patching.

Exploitation context

The supplied bundle marks KEV as false and provides no cited evidence of active exploitation. The risk is still high because the flaw is remotely reachable per CVSS, low complexity, unauthenticated, and has full CIA impact.

Researcher notes

Do not assume affected status beyond Mozilla Firefox, Firefox ESR, Thunderbird, and referenced Red Hat packages. Bugzilla may contain restricted details. The source bundle names fixed releases but does not provide exploit details, proof of exploitation, or non-Mozilla product impact.

Mitigation direction

  • Update Firefox to 149 or later where applicable.
  • Update Firefox ESR to 115.34 or 140.9 or later.
  • Update Thunderbird to 149 or 140.9 or later.
  • Apply relevant Red Hat RHSA updates for managed Linux systems.
  • Monitor Mozilla and Red Hat advisories for revised guidance.

Validation and detection

  • Inventory Firefox, Firefox ESR, and Thunderbird versions across endpoints.
  • Confirm installed versions meet or exceed the fixed Mozilla releases.
  • Check Red Hat package status against applicable RHSA advisories.
  • Review vulnerability scanner results for CVE-2026-4696 after patching.
  • Document exceptions and compensating controls for unsupported systems.
Prepared
Confidence
high
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-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