CVE-2023-23604 is a vulnerability identified in Mozilla Firefox versions earlier than 109, involving the DOMParser::ParseFromSafeString function. The issue arises when parsing non-system HTML documents, where a duplicate SystemPrincipal object can be created. The SystemPrincipal in Firefox represents a high-privilege security context, and duplication of this object can lead to bypassing web security checks that normally restrict access to sensitive browser features or data. This vulnerability falls under CWE-863 (Incorrect Authorization), indicating improper enforcement of security policies. The CVSS 3.1 base score is 6.5 (medium), with an attack vector of network (remote), low attack complexity, no privileges required, but user interaction needed (e.g., visiting a malicious webpage). The scope is unchanged, and the impact affects integrity but not confidentiality or availability. No known exploits have been reported in the wild, and no official patches were linked in the provided data, but Mozilla has released Firefox 109 which addresses this issue. The vulnerability could be exploited by attackers to bypass same-origin policies or other browser security mechanisms, potentially enabling unauthorized actions or data manipulation within the browser context. This poses risks especially in environments where web applications rely on Firefox's security model to enforce strict content isolation and authorization.

For European organizations, this vulnerability could undermine the security guarantees provided by Firefox, potentially allowing attackers to bypass web security controls and perform unauthorized actions within the browser. This could lead to integrity violations such as unauthorized script execution or manipulation of web content, which may facilitate further attacks like phishing, session hijacking, or privilege escalation within web applications. Sectors such as finance, government, and critical infrastructure that depend on secure web browsing are particularly at risk. Although confidentiality and availability are not directly impacted, the integrity compromise can have cascading effects on trustworthiness of web-based workflows and data. The requirement for user interaction limits mass exploitation but targeted attacks remain plausible. The absence of known exploits reduces immediate risk but patching remains critical to prevent future exploitation. Organizations relying on Firefox for secure web access should consider this vulnerability a moderate threat to their browser security posture.

The primary mitigation is to upgrade all Firefox installations to version 109 or later, where this vulnerability is fixed. Organizations should enforce patch management policies to ensure timely updates of browsers across all endpoints. Additionally, web application developers should avoid parsing untrusted HTML content using DOMParser::ParseFromSafeString or implement strict input validation and sanitization to reduce risk. Deploying browser security policies such as Content Security Policy (CSP) can help mitigate potential exploitation by restricting script execution and resource loading. Network-level protections like web filtering and endpoint security solutions can detect and block malicious web content attempting to exploit this vulnerability. User awareness training to avoid interacting with suspicious links or websites can further reduce risk. Monitoring browser telemetry and logs for unusual behavior related to DOM parsing or security principal anomalies can aid early detection of exploitation attempts.