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CVE Record

CVE-2026-2766: Use-after-free in the JavaScript Engine: JIT component

Use-after-free in the JavaScript Engine: JIT 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-2026-2766 is a critical memory-safety flaw in Mozilla’s JavaScript JIT engine. Mozilla says it is fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8. Because browsers and mail clients process untrusted web and message content, organizations should prioritize rapid updates.

Executive priority

Treat as an urgent endpoint patching item. The severity is critical, the affected software is common, and the flaw sits in a high-risk browser/mail client component. Prioritize managed browsers, email clients, and Linux packaged deployments.

Technical view

The issue is a use-after-free (CWE-416) in the JavaScript Engine JIT component. The CVSS 3.1 score is 9.8 with network attack vector, low complexity, no privileges, and high confidentiality, integrity, and availability impact. Public sources do not provide exploit details, and CISA KEV status is false in the bundle.

Likely exposure

Endpoints running Mozilla Firefox, Firefox ESR, Thunderbird, or downstream packaged versions before the fixed releases are the primary concern. Red Hat advisories indicate Linux distribution packages may also require vendor updates. Exposure depends on installed versions and package source.

Exploitation context

No cited source in the bundle confirms active exploitation. The risk remains high because JavaScript engine memory bugs in browsers can be reachable through untrusted content, but the public bundle does not provide proof-of-concept, exploit maturity, or attack campaign details.

Researcher notes

Public data identifies the bug class and component but not detailed root cause or exploitability mechanics. Mozilla Bugzilla may contain restricted details. Avoid assuming affected version ranges beyond Mozilla’s fixed-release statements and downstream vendor advisories.

Mitigation direction

  • Update Firefox to 148 or later where applicable.
  • Update Firefox ESR to 140.8 or later.
  • Update Thunderbird to 148 or 140.8 or later, as applicable.
  • Apply relevant Red Hat security advisories for packaged Mozilla components.
  • Check Mozilla and OS vendor guidance for environment-specific instructions.

Validation and detection

  • Inventory Firefox, Firefox ESR, and Thunderbird versions across endpoints.
  • Confirm installed versions meet or exceed Mozilla fixed releases.
  • Review Linux package manager status against applicable Red Hat errata.
  • Track CVE-2026-2766 in vulnerability management until all assets are remediated.
  • Monitor Mozilla and CISA sources for exploitation-status changes.
Prepared
Confidence
high
Sources
9

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
cve · low confidence lookup

CVE-2026-2766 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
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-2026-2766Attack 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: JIT component
other:Red Hat severity ratingcvssV3_1
  • 2026-02-24T14:02:36.100Z: Reported to Red Hat.
  • 2026-02-24T13:33:04.946Z: 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.

Open CWE intelligenceSame-CWE CVEs