LiveActive security incident?Get immediate response
CVE Record

CVE-2026-4699: Incorrect boundary conditions in the Layout: Text and Fonts component

Incorrect boundary conditions 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.

HighCVSS 7.5Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-4699 is a high-severity Mozilla flaw in text and font layout handling. The available sources describe an availability impact, meaning affected Firefox or Thunderbird versions could be made to crash or stop working. Mozilla says the issue is fixed in listed Firefox, Firefox ESR, and Thunderbird releases.

Executive priority

Prioritize normal high-severity patching. This is not supported as actively exploited by the supplied sources, but the no-privilege, no-user-interaction CVSS profile and availability impact justify timely endpoint remediation.

Technical view

The issue is described as incorrect boundary conditions in Mozilla's Layout: Text and Fonts component, associated with CWE-754 and CWE-787. CVSS 3.1 is 7.5, with network attack vector, low complexity, no privileges, no user interaction, unchanged scope, and high availability impact only.

Likely exposure

Exposure is most likely on endpoints or servers running vulnerable Firefox, Firefox ESR, or Thunderbird builds before the fixed Mozilla releases, including environments consuming Red Hat-maintained Mozilla packages covered by the referenced errata.

Exploitation context

The source bundle does not show CISA KEV listing or cited evidence of active exploitation. Public advisories identify the affected component and fixed releases, but the provided evidence does not establish real-world exploitation or provide attack details.

Researcher notes

Focus validation on version and package state rather than exploit reproduction. The bundle names boundary-condition handling in text/font layout and maps to out-of-bounds write, but does not include enough public detail to infer reliable trigger conditions.

Mitigation direction

  • Update Firefox to 149 or the fixed ESR releases named by Mozilla.
  • Update Thunderbird to 149 or 140.9 where applicable.
  • Apply relevant Red Hat security errata for packaged Firefox or Thunderbird builds.
  • Check Mozilla and OS vendor guidance for product-specific fixed package versions.

Validation and detection

  • Inventory Firefox, Firefox ESR, and Thunderbird versions across managed assets.
  • Confirm installed versions meet or exceed Mozilla's fixed releases.
  • For Red Hat systems, verify applicable RHSA errata are installed.
  • Track vendor advisories for any revised affected-version or mitigation guidance.
Prepared
Confidence
medium
Sources
12

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-754: 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-787: 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-2026-4699 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
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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: partial

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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6CISA-ADP
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-4699Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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: Incorrect boundary conditions in the Layout: Text and Fonts component
other:Red Hat severity ratingcvssV3_1
  • 2026-03-24T13:02:57.007Z: Reported to Red Hat.
  • 2026-03-24T12:30:28.441Z: 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-754CWE-787

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

CWE-754 · source CWE mapping

Improper Check for Unusual or Exceptional Conditions

Improper Check for Unusual or Exceptional Conditions represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-787 · source CWE mapping

Out-of-bounds Write

Out-of-bounds Write represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs