Same-Origin Policy Bypass in Firefox DOM Navigation

Same-origin policy bypass in the DOM: Navigation component. This vulnerability was fixed in Firefox 153, Firefox ESR 115.38, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.

Casky was already ahead

This CVE exploits attack patterns that Casky's 322matched 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-2026-16349 is a critical same-origin policy (SOP) bypass vulnerability affecting Firefox's DOM navigation component, with a CVSS score of 9.8. The same-origin policy is a foundational web security mechanism that prevents malicious scripts from accessing sensitive data across different origins. This bypass allows attackers to circumvent these protections, potentially enabling unauthorized access to sensitive user data, session tokens, or credentials from websites the user has authenticated to. The vulnerability affects Firefox versions prior to 153, Firefox ESR versions before 115.38 and 140.13, Thunderbird versions before 153 and 140.13, and any application or user relying on these browsers for secure web browsing. Given the widespread use of Firefox and the fundamental nature of the SOP protection, this vulnerability poses significant risk to enterprise and consumer users alike.

Casky's 322 mapped security skills leverage Claude AI with extended reasoning to detect the attack patterns underlying this vulnerability by correlating MITRE ATT&CK techniques TA0001 (Reconnaissance) and TA0043 (Reconnaissance), which encompass initial access and information gathering behaviors. Practitioners using Casky would identify suspicious DOM navigation patterns—such as cross-origin frame manipulation, abnormal script execution across origin boundaries, or unexpected document.domain modifications—as detectable indicators. The platform's skills would flag CWE-346 (Origin Validation Error) patterns including attempts to bypass origin checks, unusual postMessage communications between frames, and navigation flows that violate expected SOP constraints. Real-world findings would surface as anomalous browser behavior during security assessments, such as scripts unexpectedly accessing resources from different origins or DOM events triggered from unauthorized cross-origin contexts, enabling defenders to patch affected systems before exploitation occurs.

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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 →

322 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-16349.

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-2026-16349

Casky has 322 skills that investigate the attack patterns behind CVE-2026-16349. Run one and get CVSS-scored findings in 3 minutes.

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