DOM Navigation Component Privilege Escalation in Firefox

Privilege escalation in the DOM: Navigation 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.

Casky was already ahead

This CVE exploits attack patterns that Casky's 224matched 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-2026-74939 represents a critical privilege escalation vulnerability in Firefox's DOM Navigation component, allowing attackers to bypass security boundaries and gain elevated privileges within the browser context. This vulnerability affects multiple Mozilla products including Firefox, Firefox ESR (versions 115, 140, and 153), Thunderbird, and their respective ESR releases. The high CVSS score of 8.8 reflects the severity of this flaw—privilege escalation vulnerabilities are particularly dangerous because they enable attackers to move laterally within a system, access sensitive data, or execute arbitrary code with elevated permissions. Organizations running these affected Mozilla applications, particularly those in critical infrastructure or handling sensitive information, face significant risk if they haven't applied the necessary patches.

Casky.ai's 224 mapped security skills leverage Claude AI with extended reasoning to detect the attack patterns associated with TA0004 (Privilege Escalation) techniques underlying this vulnerability. Practitioners using the platform would observe detection signatures focused on DOM manipulation anomalies, unexpected navigation state changes, and privilege boundary violations within browser processes. The skills map to CWE-269 (Improper Access Control), enabling detection of unauthorized capability transitions in the DOM layer. Security teams would see findings highlighting suspicious script execution patterns that attempt to escalate from standard to elevated privilege levels, unusual iframe or window object interactions that bypass navigation security controls, and process behavior deviations that indicate exploitation attempts. By correlating these attack indicators against MITRE ATT&CK's privilege escalation framework, practitioners can identify both active exploitation and post-compromise persistence techniques that leverage this vulnerability.

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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 →

224 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-74939.

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

Access with Stolen Session Cookie

penetration testing · medium

Run

MITRE ATT&CK Techniques

TA0004

Investigate the attack patterns behind CVE-2026-74939

Casky has 224 skills that investigate the attack patterns behind CVE-2026-74939. Run one and get CVSS-scored findings in 3 minutes.

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