PatchSiren

PatchSiren cyber security CVE debrief

CVE-2026-74934 Mozilla CVE debrief

Site isolation issue in the Graphics: CanvasWebGL component. This vulnerability was fixed in Firefox 154, Firefox ESR 115.39, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1. The vulnerability relates to site isolation, a security feature that helps prevent malicious scripts from accessing sensitive data. Affected users and administrators should prioritize patch deployment to prevent exploitation. The CVE record and NVD detail provide information on this issue, and defenders should verify patch deployment and review system logs for suspicious activity.

Vendor
Mozilla
Product
Firefox
CVSS
HIGH 7.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-08-18
Original CVE updated
2026-08-24
Advisory published
2026-08-18
Advisory updated
2026-08-24

Who should care

Users of Firefox, Thunderbird, and related products should apply patches to prevent exploitation of this site isolation vulnerability. Additionally, security teams and IT administrators responsible for managing these applications should prioritize patch deployment and review system configurations for potential exposure. Vulnerability management and security teams should also monitor for compensating controls and verify patch deployment across their environments.

Technical summary

The site isolation issue in the Graphics: CanvasWebGL component was fixed in multiple Firefox, Firefox ESR, Thunderbird versions. This vulnerability has a CVSS score of 7.5 and is classified as HIGH severity. The issue relates to site isolation, which is a security feature that helps prevent malicious scripts from accessing sensitive data. The vulnerability was addressed through patches in various Firefox and Thunderbird versions, indicating its potential impact on web application security.

Defensive priority

Apply vendor patches for Firefox, Thunderbird, and related products to prevent exploitation of site isolation vulnerabilities.

Recommended defensive actions

  • Apply Firefox 154 and related patches
  • Apply Thunderbird 154 and related patches
  • Inventory checks for affected products
  • Monitor for compensating controls
  • Exception tracking for incomplete mitigation

Evidence notes

The CVE record and NVD detail provide information on the site isolation issue in the Graphics: CanvasWebGL component. Mozilla has released advisories (MFSA2026-74 to MFSA2026-80) and bug reports (e.g., bug 2050584) related to this vulnerability. The vulnerability was fixed in Firefox 154, Firefox ESR 115.39, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1. However, details on affected scope, exploitation, and specific defensive measures are limited. Defenders should verify patch deployment, review system logs for suspicious activity, and monitor for potential compensating controls.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-74934 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-74934

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

  • CVE-2026-74934 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-74934

    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.