CVE-2025-11153 is a vulnerability identified in the Just-In-Time (JIT) compilation component of the JavaScript engine used by Mozilla Firefox versions prior to 143.0.3. The JIT compiler is responsible for dynamically translating JavaScript code into optimized machine code at runtime to improve performance. A miscompilation flaw in this component means that the JIT compiler may incorrectly translate certain JavaScript code sequences, potentially leading to unexpected behavior such as memory corruption, execution of arbitrary code, or other security-critical issues. Although specific technical details such as the exact nature of the miscompilation or the exploited code patterns are not provided, such vulnerabilities typically arise from incorrect assumptions or logic errors in the optimization passes of the JIT engine. The vulnerability was reserved on September 29, 2025, and published the following day, indicating a recent discovery. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet. The affected product is Mozilla Firefox, a widely used web browser, and the vulnerability affects all versions prior to 143.0.3, though exact affected versions are unspecified. Given the critical role of the JavaScript engine in rendering web content and executing scripts, exploitation could allow attackers to execute arbitrary code within the context of the browser, potentially leading to full compromise of the user's session or system depending on sandboxing and other mitigations. This type of vulnerability is particularly dangerous because it can be triggered by malicious web content without requiring user interaction beyond visiting a crafted webpage.

For European organizations, this vulnerability poses a significant risk due to the widespread use of Mozilla Firefox across both enterprise and public sectors. Successful exploitation could lead to remote code execution, allowing attackers to bypass security controls, steal sensitive data, or deploy malware within corporate networks. This is especially concerning for organizations handling sensitive personal data under GDPR regulations, as breaches could result in regulatory penalties and reputational damage. The vulnerability could be leveraged in targeted attacks against government institutions, financial services, healthcare providers, and critical infrastructure operators, all of which commonly use Firefox as part of their standard IT environment. Additionally, the lack of known exploits currently suggests a window of opportunity for defenders to patch systems before active exploitation begins. However, the ease of exploitation is potentially high since the vulnerability resides in a browser component that processes untrusted web content, which is frequently accessed by users. The impact on confidentiality, integrity, and availability is potentially severe, as arbitrary code execution could lead to data exfiltration, system manipulation, or denial of service.

European organizations should prioritize updating Mozilla Firefox to version 143.0.3 or later immediately upon release to remediate this vulnerability. Until patches are applied, organizations should implement network-level protections such as web filtering and intrusion prevention systems to block access to known malicious or suspicious websites that could host exploit code. Employing browser isolation technologies can also reduce the risk by executing web content in sandboxed environments separate from critical systems. Security teams should monitor threat intelligence feeds for any emerging exploit attempts related to CVE-2025-11153 and conduct internal vulnerability scanning to identify and remediate outdated Firefox installations. Additionally, enforcing strict content security policies (CSP) and disabling unnecessary browser extensions can reduce the attack surface. User awareness training should emphasize cautious browsing habits and the risks of visiting untrusted sites. Finally, organizations should review and enhance endpoint detection and response (EDR) capabilities to detect anomalous behavior indicative of exploitation attempts.