Firefox DOM Navigation Site Isolation Bypass

Site isolation issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird 153.2.

Casky was already ahead

This CVE exploits attack patterns that Casky's 323matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

CVE-2026-84129 is a critical site isolation vulnerability affecting Firefox's DOM Navigation component with a CVSS score of 9.8. Site isolation is a fundamental security boundary designed to prevent cross-site data leakage by ensuring malicious scripts cannot access sensitive information from other domains. This flaw bypasses that protection, allowing attackers to potentially exfiltrate data across domain boundaries or escalate privileges within the browser sandbox. Users of Firefox, Firefox ESR, Thunderbird, and Thunderbird 153.2 and earlier versions are at immediate risk, as the vulnerability enables attackers to circumvent browser security models that users typically rely upon for safe web browsing and email usage.

Casky's 323 matched security skills leverage Claude AI's extended reasoning to correlate attack patterns associated with TA0001 (Reconnaissance) and TA0043 (Reconnaissance for defense evasion). Practitioners using Casky would observe detections aligned with CWE-346 (Origin Validation Error) behavioral patterns—specifically anomalous DOM navigation sequences that cross security boundaries without proper origin verification. The platform would flag suspicious iframe navigation attempts, postMessage communications between mismatched origins, and JavaScript execution contexts that violate expected isolation policies. By mapping these indicators to MITRE ATT&CK, defenders would identify pre-exploitation reconnaissance activities where attackers probe DOM navigation mechanisms, followed by delivery attempts that leverage this isolation bypass to establish persistence or exfiltrate credential data across domain contexts.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →

323 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-84129.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

Run

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

MITRE ATT&CK Techniques

TA0001 TA0043

Investigate the attack patterns behind CVE-2026-84129

Casky has 323 skills that investigate the attack patterns behind CVE-2026-84129. Run one and get CVSS-scored findings in 3 minutes.

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