CVE-2025-54812 is a vulnerability classified under CWE-117 (Improper Output Neutralization for Logs) found in Apache Log4cxx versions prior to 1.5.0. The issue arises specifically when the logging framework is configured to use the HTMLLayout, which formats log entries as HTML files. In this scenario, logger names are not properly escaped before being written into the HTML log output. If an attacker can influence or control the logger name—typically a string used to identify the source of log messages—they can inject malicious HTML or JavaScript code into the log file. When a user subsequently opens this HTML log file in a web browser, the injected script can execute, resulting in a cross-site scripting (XSS) attack. This could allow attackers to hide log entries, manipulate log content, or potentially steal sensitive information from the user viewing the logs. However, exploitation requires several conditions: the use of HTMLLayout, logger names derived from untrusted input, and user interaction to open the HTML log file. Logger names are generally static and controlled by developers, limiting the attack surface. The vulnerability has a CVSS 4.0 base score of 2.1, reflecting low severity due to the complexity and limited impact. The issue is resolved in Apache Log4cxx version 1.5.0, which properly escapes logger names in HTMLLayout outputs.

For European organizations, the impact of CVE-2025-54812 is generally low but context-dependent. Organizations that generate HTML logs using Apache Log4cxx with HTMLLayout and allow untrusted input to influence logger names are at risk of XSS attacks when logs are viewed in browsers. This could lead to misleading log information, concealment of malicious activity, or theft of sensitive data from users viewing the logs. While the direct impact on confidentiality, integrity, and availability is limited, the vulnerability could aid attackers in covering tracks or conducting social engineering attacks via malicious log content. Critical sectors such as finance, healthcare, and government that rely on detailed logging for auditing and compliance may find such manipulation problematic. However, since exploitation requires user interaction and specific configuration, the overall risk remains low. European organizations should assess their use of Log4cxx, especially in environments where HTML logs are generated and viewed, to determine exposure.

1. Upgrade Apache Log4cxx to version 1.5.0 or later, where the vulnerability is fixed by proper escaping of logger names in HTMLLayout. 2. Avoid using HTMLLayout for logging if possible, especially if untrusted input might influence logger names. 3. Ensure logger names are static and controlled by the application, never derived from user input or untrusted sources. 4. Implement strict input validation and sanitization on any data that could influence logger names or other log metadata. 5. Educate users and administrators to avoid opening HTML log files from untrusted sources or environments. 6. Consider alternative logging formats (e.g., plain text or JSON) that do not render in browsers or execute scripts. 7. Monitor logs for suspicious entries that could indicate attempts to inject malicious content. 8. Apply principle of least privilege to limit who can configure logging and access log files. 9. Integrate log integrity verification mechanisms to detect tampering. 10. Regularly review and audit logging configurations and practices to ensure compliance with security policies.