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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 Mozilla memory-safety flaw in the JavaScript JIT engine. Mozilla says it was fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8. Treat unmanaged browsers and mail clients below those fixed releases as urgent patch targets.

Executive priority

Prioritize remediation this cycle, especially on user workstations and systems using Mozilla packages. There is no active-exploitation evidence in the supplied sources, but the critical score and browser JavaScript engine location make delayed patching a material endpoint risk.

Technical view

The issue is a CWE-416 use-after-free in Mozilla's JavaScript Engine JIT component. The provided CVSS 3.1 vector is 9.8 critical, network-accessible, low complexity, no privileges, no user interaction, with high confidentiality, integrity, and availability impact.

Likely exposure

Exposure is most likely on endpoints and servers running Mozilla Firefox, Firefox ESR, or Thunderbird before the applicable fixed release. Linux environments may also be exposed through Red Hat-distributed Mozilla packages referenced by RHSA advisories.

Exploitation context

The bundle does not show CISA KEV listing and provides no cited evidence of active exploitation. No public exploit details are included. The risk remains high because JavaScript JIT use-after-free bugs are commonly serious memory-corruption issues.

Researcher notes

Focus validation on version and package state, not exploit reproduction. The source bundle identifies the bug class, component, fixed releases, CVSS vector, Mozilla advisories, and Red Hat downstream advisories, but does not provide exploitability details or proof-of-concept evidence.

Mitigation direction

  • Upgrade Firefox to 148 or the applicable fixed ESR release.
  • Upgrade Thunderbird to 148 or the applicable fixed ESR release.
  • Apply relevant Red Hat RHSA updates where Mozilla packages are managed by Red Hat.
  • Check Mozilla and OS vendor advisories for platform-specific package names.
  • Prioritize patching managed endpoints with browser or email client internet exposure.

Validation and detection

  • Inventory Firefox, Firefox ESR, and Thunderbird versions across managed assets.
  • Confirm versions meet or exceed Mozilla's fixed releases listed for this CVE.
  • Check Red Hat systems for applicable RHSA package update status.
  • Review vulnerability scanner results against CVE-2026-2766 after patching.
  • Document exceptions where vendor packages are not yet available.
Prepared
Confidence
high
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-2026-2766 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-2026-2766Attack 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.

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