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CVE Record

CVE-2026-2765: Use-after-free in the JavaScript Engine component

Use-after-free in the JavaScript Engine component. This vulnerability was fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

CriticalCVSS 9.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

CVE-2026-2765 is a critical Mozilla JavaScript engine memory-safety flaw. Mozilla says it was fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8. For leaders, the main concern is rapid exposure across workstations and managed Linux packages, not confirmed active exploitation.

Executive priority

Prioritize remediation in the next emergency patch cycle. The sources do not prove exploitation, but the severity, memory-corruption class, and broad browser/email-client footprint justify fast action.

Technical view

The issue is a CWE-416 use-after-free in Mozilla’s JavaScript Engine component with CVSS 3.1 score 9.8. The supplied 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. Public sources here do not include root-cause detail or proof-of-concept material.

Likely exposure

Organizations may be exposed where Firefox or Thunderbird are installed below the fixed Mozilla releases or via downstream packages awaiting vendor updates. Red Hat advisories and VEX data indicate enterprise Linux package tracking is relevant.

Exploitation context

The provided bundle does not show KEV listing or confirmed active exploitation. Treat as urgent because Mozilla and Red Hat issued security updates and the CVSS vector indicates low-complexity network attack potential without privileges.

Researcher notes

Public detail is limited in the supplied sources. Do not assume exploitability mechanics beyond the CVSS vector and use-after-free classification. Focus validation on version/package state, vendor errata mapping, and whether downstream distributions have shipped patched builds.

Mitigation direction

  • Upgrade Firefox to 148 or Firefox ESR to 140.8 where applicable.
  • Upgrade Thunderbird to 148 or Thunderbird 140.8 where applicable.
  • Apply relevant Red Hat security advisories for packaged Mozilla components.
  • Check Mozilla and OS vendor guidance for any newer superseding fixes.
  • Prioritize managed workstation and server images that include Firefox or Thunderbird.

Validation and detection

  • Inventory Firefox and Thunderbird versions across endpoints and base images.
  • Confirm installed versions meet or exceed the named fixed releases.
  • Check Linux package status against relevant Red Hat advisories and VEX data.
  • Review vulnerability scanner results for CVE-2026-2765 after patch deployment.
  • Verify exception lists do not include outdated Mozilla packages.
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-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.

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cve · low confidence lookup

CVE-2026-2765 mapping review

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

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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
34Source 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-2026-2765Attack 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 JavaScript Engine component
other:Red Hat severity ratingcvssV3_1
  • 2026-02-24T14:05:05.206Z: Reported to Red Hat.
  • 2026-02-24T13:33:03.943Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MozillaFirefox140.8, 148Listed
MozillaThunderbird140.8, 148Listed
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.

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