LiveActive security incident?Get immediate response
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
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

CVE-2026-2765 is a critical Mozilla JavaScript engine use-after-free vulnerability fixed in Firefox 148, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8. If exposed versions remain deployed, a successful attack could compromise confidentiality, integrity, and availability according to the supplied CVSS data.

Executive priority

Prioritize remediation in the next emergency patch cycle. The vulnerability is critical, remotely reachable per CVSS, and affects common browser and mail software, but active exploitation is not evidenced in the provided sources.

Technical view

The issue is classified as CWE-416, use-after-free, in Mozilla's JavaScript Engine component. The source bundle assigns CVSS 3.1 score 9.8 with network attack vector, low complexity, no privileges, and high impact across confidentiality, integrity, and availability.

Likely exposure

Exposure is most likely where organizations run Mozilla Firefox, Firefox ESR, Thunderbird, or Red Hat-packaged variants below the fixed releases referenced by Mozilla and Red Hat advisories.

Exploitation context

The bundle does not show CISA KEV listing and provides no cited evidence of active exploitation. Treat as urgent because the CVSS score is critical and the affected component processes web or message content.

Researcher notes

Avoid assuming exploit availability from CVSS alone. The useful validation path is version and package verification against Mozilla fixed releases and Red Hat errata. Bug details may be restricted or incomplete, so rely on vendor advisories for remediation scope.

Mitigation direction

  • Upgrade Firefox to the fixed Mozilla release specified by vendor guidance.
  • Upgrade Firefox ESR and Thunderbird to the fixed versions listed by Mozilla.
  • Apply relevant Red Hat RHSA updates for vendor-packaged builds.
  • Check Mozilla and Red Hat advisories for platform-specific package names.
  • Prioritize managed endpoints and systems handling untrusted web or email content.

Validation and detection

  • Inventory Firefox, Firefox ESR, and Thunderbird versions across endpoints.
  • Confirm installed versions meet or exceed the fixed releases in Mozilla advisories.
  • Check Red Hat package status against linked RHSA advisories.
  • Review vulnerability scanner findings for CVE-2026-2765 after updates.
  • Verify no unsupported Mozilla builds remain in standard images.
Prepared
Confidence
high
Sources
11

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-2026-2765 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-2026-2765Attack 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.

Open CWE intelligenceSame-CWE CVEs