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CVE Record

CVE-2026-4689: Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component

Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

CriticalCVSS 10Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

CVE-2026-4689 is a critical Mozilla sandbox escape fixed in Firefox and Thunderbird updates. A successful attack could break out of browser or mail-client isolation and compromise confidentiality, integrity, and availability. The bundle does not identify active exploitation, but the CVSS 10 score makes patching urgent.

Executive priority

Treat this as an urgent patching item for browsers and mail clients. No active exploitation is cited, but sandbox escape plus CVSS 10 creates high business risk if updates lag on user endpoints.

Technical view

Mozilla describes incorrect boundary conditions and integer overflow in an XPCOM component, classified under CWE-120 and CWE-190. The CVSS v3.1 vector is AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H. Fixed releases are Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

Likely exposure

Organizations with unmanaged or delayed Firefox and Thunderbird updates are the main exposure. Red Hat references indicate downstream Linux packages also require attention. The source bundle does not provide complete vulnerable version ranges, so treat versions before the named fixed releases as suspect until vendor guidance confirms otherwise.

Exploitation context

The bundle marks KEV as false and provides no cited evidence of active exploitation or public exploit availability. Risk is still high because the vulnerability is remotely reachable by CVSS, requires no privileges or user interaction, changes scope, and can produce full confidentiality, integrity, and availability impact.

Researcher notes

Useful evidence is limited to Mozilla’s description, fixed releases, CVSS, CWE mapping, and Red Hat downstream advisories. Do not infer exploitability beyond the vector and sandbox-escape description. Confirm exact vulnerable ranges and platform package status from vendor advisories.

Mitigation direction

  • Upgrade Firefox to 149 or ESR 115.34/140.9 as applicable.
  • Upgrade Thunderbird to 149 or 140.9 as applicable.
  • Apply relevant Red Hat security errata for packaged Mozilla components.
  • Check Mozilla and OS vendor advisories for exact affected ranges.
  • Prioritize managed endpoints, VDI images, and shared workstations.

Validation and detection

  • Inventory installed Firefox and Thunderbird versions across endpoints.
  • Confirm fixed versions are deployed, not merely downloaded.
  • Review Red Hat errata applicability for Linux fleets.
  • Check vulnerability scanner findings against CVE-2026-4689.
  • Verify update deferrals or package pins are removed.
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-120: 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-190: 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-2026-4689 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
10 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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
10CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H3.96CISA-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

10Critical
CVSS 3.1 vector shape for CVE-2026-4689Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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 due to incorrect boundary conditions, integer overflow in the XPCOM component
other:Red Hat severity ratingcvssV3_1
  • 2026-03-24T13:01:48.103Z: Reported to Red Hat.
  • 2026-03-24T12:30:23.260Z: 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-120CWE-190

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

CWE-120 · source CWE mapping

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-190 · source CWE mapping

Integer Overflow or Wraparound

Integer Overflow or Wraparound represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs