CVE-2025-54812 is a vulnerability classified under CWE-117 (Improper Output Neutralization for Logs) affecting the Apache Software Foundation's Apache Log4cxx library prior to version 1.5.0. The issue arises when Log4cxx is configured to use the HTMLLayout for logging output. Specifically, logger names are not properly escaped or sanitized when written to HTML log files. If an attacker can influence or control the logger name—by supplying untrusted input as the logger identifier—they could inject malicious HTML or JavaScript code into the generated log files. When these HTML log files are viewed in a web browser, the injected code could execute, potentially enabling cross-site scripting (XSS) attacks. This could allow attackers to hide log information, manipulate log content, or steal data from users viewing the logs. However, exploitation requires a specific sequence: the use of HTMLLayout, logger names derived from untrusted input, and the victim opening the resulting HTML log file in a browser. Since logger names are typically static and controlled by developers, the likelihood of exploitation is low, and the overall impact is assessed as low. The vulnerability has a CVSS 4.0 score of 2.1, reflecting low severity due to the limited attack vector and impact. The issue is resolved in Apache Log4cxx version 1.5.0, and users are advised to upgrade to this version to mitigate the risk.

For European organizations, the direct impact of this vulnerability is limited due to the low likelihood of exploitation and the specific conditions required. However, organizations that use Apache Log4cxx with HTMLLayout for logging and that incorporate untrusted input into logger names could face risks of log manipulation or XSS attacks when viewing logs in browsers. This could undermine the integrity and reliability of log data, which is critical for security monitoring and forensic investigations. In regulated industries such as finance, healthcare, and critical infrastructure within Europe, compromised logs could hinder compliance and incident response efforts. Additionally, if attackers use this vulnerability to conceal malicious activity within logs, it could delay detection of more severe attacks. While the vulnerability does not directly compromise system confidentiality or availability, the potential for data theft via XSS and log tampering poses a reputational risk and could facilitate further attacks if combined with other vulnerabilities.

European organizations should take the following specific steps beyond generic advice: 1) Immediately upgrade all Apache Log4cxx deployments to version 1.5.0 or later, where the vulnerability is fixed. 2) Audit logging configurations to identify any use of HTMLLayout and assess whether logger names are derived from untrusted or external input. 3) Where HTMLLayout is necessary, implement input validation or sanitization on logger names to prevent injection of malicious content. 4) Restrict access to log files, especially HTML logs, to trusted personnel and avoid opening them in untrusted or public browsers. 5) Consider switching to alternative logging layouts that do not render logs as HTML if HTML output is not essential. 6) Incorporate log integrity verification mechanisms, such as cryptographic hashes or append-only logging, to detect tampering. 7) Train security and operations teams to recognize suspicious log entries and understand the risks of XSS in log files. 8) Monitor for any unusual activity related to logging components and review logs regularly for anomalies.