LiveActive security incident?Get immediate response
CVE Record

CVE-2026-84119: Sandbox escape due to use-after-free in the DOM: Navigation component

Sandbox escape due to use-after-free in the DOM: Navigation component. This vulnerability was fixed in Firefox 155, Firefox ESR 115.40, Firefox ESR 140.15, Firefox ESR 153.2, Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

CriticalCVSS 9.6Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

A memory-safety flaw in Firefox and Thunderbird can let malicious content escape a software sandbox after user interaction. Successful exploitation could cross a security boundary and seriously affect data confidentiality, integrity, and availability. Mozilla fixed the issue in the specified releases, so potentially unpatched endpoints require urgent attention.

Executive priority

Treat this as an immediate patching priority for user endpoints running Firefox or Thunderbird. The potential impact is critical, although exploitation requires user interaction and active attacks are not established by the supplied evidence. Ask owners to identify potentially exposed installations, deploy the applicable fixed versions, and report verified coverage.

Technical view

CVE-2026-84119 is a CWE-416 use-after-free in the DOM Navigation component. Its CVSS 3.1 score is 9.6: network-accessible, low complexity, no privileges required, user interaction required, and changed scope, with high confidentiality, integrity, and availability impacts. The supplied evidence does not describe the trigger or exact vulnerable release ranges.

Likely exposure

Firefox or Thunderbird installations not running an applicable fixed release should be treated as potentially exposed. Fixed versions are Firefox 155; Firefox ESR 115.40, 140.15, and 153.2; Thunderbird 155, 140.15, and 153.2. The bundle does not identify exact vulnerable version ranges or platform-specific differences.

Exploitation context

The bundle marks KEV as false and provides no evidence of active exploitation or a public exploit. The CVSS vector indicates remote reachability, low attack complexity, no required privileges, and required user interaction. These characteristics support urgent remediation but do not prove reliable exploitation is currently available.

Researcher notes

The source bundle establishes a DOM Navigation use-after-free, sandbox escape, CVSS 9.6 rating, and fixed releases. It does not provide affected-version ranges, technical trigger details, exploit-chain requirements, proof-of-concept availability, or observed exploitation. The listed versions should be interpreted as fixes, despite their appearance in the bundle's affected-product records.

Mitigation direction

  • Update Firefox to 155, or ESR 115.40, 140.15, or 153.2 as appropriate.
  • Update Thunderbird to 155, 140.15, or 153.2 as appropriate.
  • Use Mozilla advisories to select the correct supported release channel for each deployment.
  • If updating is delayed, consult Mozilla guidance; the bundle names no alternative workaround.

Validation and detection

  • Inventory all Firefox and Thunderbird installations, including unmanaged and remote endpoints.
  • Compare each installation against the applicable fixed release and update channel.
  • Verify updates completed successfully using endpoint management or software inventory records.
  • Recheck Mozilla advisories for clarified affected ranges, platform notes, or revised guidance.
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-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
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-2026-84119 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
9.6 (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.

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

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical 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
9.6CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H2.86CISA-ADP

Vulnerability scoring details

Base CVSS 3.1 score

9.6Critical
CVSS 3.1 vector shape for CVE-2026-84119Attack 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. 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, 155Listed
MozillaThunderbird140.15, 153.2, 155Listed
Weakness

CWE details

CWE-416

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