CVE-2025-13017 is a vulnerability identified in Mozilla Firefox and Thunderbird that allows bypassing the same-origin policy (SOP) within the DOM Notifications component. The same-origin policy is a critical security mechanism that restricts how documents or scripts loaded from one origin can interact with resources from another origin, preventing malicious cross-site interactions. This vulnerability affects Firefox versions earlier than 145, Firefox ESR versions earlier than 140.5, and corresponding Thunderbird versions. The flaw lies in the Notifications component of the DOM, which improperly enforces SOP, enabling an attacker to bypass these restrictions. An attacker could craft a malicious webpage that, when visited by a user, could exploit this flaw to access or manipulate data from other origins that should be isolated, potentially exposing sensitive information or altering content without authorization. The CVSS v3.1 base score is 8.1, indicating high severity, with an attack vector of network (remote exploitation), low attack complexity, no privileges required, but user interaction is necessary (e.g., visiting a malicious site). The impact on confidentiality and integrity is high, while availability remains unaffected. No known exploits have been reported in the wild yet. The vulnerability is tracked under CWE-942 (Improper Enforcement of Restrictions on DOM Nodes). Mozilla has not yet published patches or updates at the time of this report, but affected users are advised to monitor for updates and apply them promptly once available.

For European organizations, this vulnerability poses a significant risk to data confidentiality and integrity, particularly for entities relying heavily on Firefox and Thunderbird for web browsing and email communications. Attackers exploiting this flaw could gain unauthorized access to sensitive information from other web origins, potentially leading to data breaches, credential theft, or manipulation of web content. This is especially critical for sectors handling sensitive personal data, such as finance, healthcare, and government institutions, which are subject to strict data protection regulations like GDPR. The requirement for user interaction means phishing or social engineering campaigns could be used to trigger exploitation. The lack of availability impact means systems remain operational, potentially allowing stealthy data exfiltration or manipulation without immediate detection. The absence of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, as attackers may develop exploits rapidly once the vulnerability is public. Organizations failing to update promptly could face targeted attacks leveraging this vulnerability.

European organizations should prioritize updating Mozilla Firefox and Thunderbird to versions 145 and ESR 140.5 or later as soon as patches are released. Until updates are available, organizations should implement strict content security policies (CSP) to restrict the execution of untrusted scripts and reduce the risk of malicious content triggering the vulnerability. Employ browser isolation technologies to limit exposure of internal systems to potentially malicious web content. Educate users about the risks of interacting with untrusted websites and phishing attempts, emphasizing cautious behavior when clicking links or opening attachments. Network-level protections such as web filtering and intrusion detection systems should be tuned to detect and block known malicious URLs or payloads exploiting this vulnerability. Regularly audit and monitor browser and email client usage to ensure compliance with updated versions. Consider deploying endpoint detection and response (EDR) solutions capable of identifying anomalous browser behaviors indicative of exploitation attempts. Finally, maintain an incident response plan that includes scenarios involving browser-based SOP bypasses.