Mozilla Firefox Multiple Vulnerabilities

On May 7, 2026, Mozilla released security advisories addressing vulnerabilities in Firefox and Firefox ESR. The advisories cover Firefox versions prior to 150.0.2, Firefox ESR versions prior to 140.10.2, and Firefox ESR versions prior to 115.35.2. These vulnerabilities could be exploited by attackers if the affected browsers are not updated. Users and administrators are urged to review the Mozilla security advisories and apply the necessary updates to mitigate potential risks. Failure to update could expose users to various attack vectors, depending on the specific vulnerabilities patched in each release.

Attack Chain

Given the limited information in the advisory, the following attack chain is generalized based on common browser exploitation techniques:

1. An attacker identifies a vulnerable Firefox or Firefox ESR version (prior to 150.0.2, 140.10.2, or 115.35.2 respectively).
2. The attacker crafts a malicious web page or injects malicious code into a legitimate website.
3. The victim visits the malicious website or a compromised legitimate website using the vulnerable Firefox browser.
4. The malicious code exploits a vulnerability in the browser’s rendering engine (e.g., JavaScript engine, HTML parser) to achieve arbitrary code execution.
5. The attacker gains control of the browser process.
6. The attacker may then use the compromised browser process to escalate privileges or access sensitive information stored in the browser (e.g., cookies, saved passwords).
7. The attacker pivots from the browser to the underlying operating system to install malware, establish persistence, or exfiltrate data.
8. The attacker achieves their final objective, such as data theft, system compromise, or denial of service.

Impact

Successful exploitation of these vulnerabilities could lead to arbitrary code execution, information disclosure, or denial of service. The impact ranges from individual user compromise to potential enterprise-wide breaches if vulnerable browsers are widely deployed. The number of potential victims is substantial given the widespread use of Firefox and Firefox ESR. Organizations that fail to patch these vulnerabilities are at increased risk of compromise.

Recommendation

• Immediately update Firefox to version 150.0.2 or later.
• Immediately update Firefox ESR to version 140.10.2 or later.
• Immediately update Firefox ESR to version 115.35.2 or later.
• Deploy the Sigma rule “Detect Suspicious Firefox Child Processes” to identify potential post-exploitation activity.
• Monitor web server logs for suspicious activity originating from Firefox user agents to detect potential exploitation attempts (see “Detect Suspicious Firefox User Agent” rule).