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PatchSiren cyber security CVE debrief

CVE-2026-8964 Mozilla CVE debrief

CVE-2026-8964 is a Mozilla spoofing issue in the Popup Blocker component. Mozilla states the issue was fixed in Firefox 151 and Thunderbird 151. NVD rates it HIGH with network attack vector and no privileges required, but the available impact is limited to integrity.

Vendor
Mozilla
Product
Firefox
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-19
Original CVE updated
2026-07-23
Advisory published
2026-05-19
Advisory updated
2026-07-23

Who should care

Organizations and individuals running Mozilla Firefox or Thunderbird versions earlier than 151.0.0 should care most, especially where browser or mail-client trust decisions matter.

Technical summary

The official record describes a spoofing issue in the Popup Blocker component. NVD lists the weakness as CWE-451 and scores the issue CVSS 3.1 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N), indicating a remotely reachable integrity-impacting problem with no confidentiality or availability impact recorded. The vulnerable CPE criteria in NVD apply to Firefox and Thunderbird versions before 151.0.0.

Defensive priority

High for affected deployments. The combination of network reachability, no required privileges, and integrity impact makes version remediation a priority, even though the source corpus does not describe availability or confidentiality impact.

Recommended defensive actions

  • Upgrade Firefox to 151 or later.
  • Upgrade Thunderbird to 151 or later.
  • Confirm deployed Firefox and Thunderbird versions are not below 151.0.0.
  • Use the Mozilla advisories to validate remediation status in your environment.
  • Track endpoint and software inventory for any lingering affected installations.

Evidence notes

This debrief is based only on the supplied NVD record and Mozilla reference links. The source corpus shows affected versions ending before 151.0.0 for Firefox and Thunderbird, and it does not include exploit details or a KEV designation. CVE timing is taken from the provided published and modified timestamps.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-8964 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-8964

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-8964 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-8964

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.