CVE-2025-55668 is a session fixation vulnerability classified under CWE-384, found in the Apache Tomcat server's rewrite valve component. The flaw exists in versions 9.0.0.M1 through 9.0.105, 10.1.0-M1 through 10.1.41, and 11.0.0-M1 through 11.0.7. Session fixation attacks allow an adversary to set or fix a user's session identifier before authentication, enabling them to hijack the session once the user logs in. This vulnerability arises because the rewrite valve does not properly regenerate or invalidate session identifiers upon authentication or session establishment, allowing attackers to coerce users into authenticating with a session ID known to the attacker. The CVSS 3.1 base score is 6.5, reflecting a network attack vector with low complexity, no privileges required, but requiring user interaction. The impact is high on confidentiality as attackers can impersonate legitimate users, but integrity and availability are not affected. No public exploits have been reported yet, but the vulnerability is significant due to the widespread use of Apache Tomcat in enterprise and web application environments. The recommended fix is to upgrade to Apache Tomcat versions 9.0.106, 10.1.42, or 11.0.8, which address this issue by ensuring proper session management and regeneration of session IDs during authentication flows.

For European organizations, this vulnerability poses a risk of unauthorized access to sensitive web applications hosted on Apache Tomcat servers. Attackers exploiting this flaw can hijack user sessions, potentially gaining access to confidential data, internal systems, or administrative interfaces without needing credentials. This can lead to data breaches, compliance violations (e.g., GDPR), and reputational damage. Sectors such as finance, healthcare, government, and critical infrastructure are particularly vulnerable due to their reliance on secure web services. The medium severity score indicates a moderate but tangible risk, especially in environments where session management is critical. Since exploitation requires user interaction, phishing or social engineering could be used to lure victims into using attacker-controlled session IDs. The absence of known exploits currently reduces immediate risk but does not eliminate the threat, especially as attackers often develop exploits rapidly after disclosure.

1. Upgrade Apache Tomcat to the fixed versions: 9.0.106, 10.1.42, or 11.0.8 as soon as possible to ensure the vulnerability is patched. 2. Review and harden session management policies, ensuring session IDs are regenerated upon authentication and that session fixation protections are enabled. 3. Implement web application firewalls (WAFs) to detect and block suspicious session fixation attempts or abnormal session behaviors. 4. Educate users about phishing and social engineering risks that could facilitate session fixation exploitation. 5. Conduct regular security assessments and penetration testing focusing on session management vulnerabilities. 6. Monitor logs for unusual session activity or repeated session ID reuse patterns. 7. For legacy or EOL Tomcat versions that cannot be immediately upgraded, consider isolating affected services behind additional security layers or reverse proxies that can enforce session security controls.