CVE-2025-59476 is a vulnerability in Jenkins, a widely used open-source automation server for continuous integration and delivery. Versions 2.527 and earlier, including LTS 2.516.2 and earlier, do not properly restrict or sanitize characters inserted into log messages from user-controlled content. Specifically, attackers able to influence log message content can insert line break characters, which allows them to create forged log entries that appear legitimate. This manipulation can mislead administrators or security personnel reviewing logs by obscuring or fabricating events, potentially hiding malicious activity or causing incorrect operational decisions. The vulnerability falls under CWE-117, which involves improper output neutralization for logs, a common issue that can undermine the trustworthiness of audit trails. The CVSS v3.1 base score is 5.3 (medium severity), reflecting that the attack vector is network-based with low complexity, no privileges or user interaction required, and impacts only the integrity of logs without affecting confidentiality or availability. No patches or exploits are currently documented, but the risk lies in the potential for attackers to evade detection or mislead incident response through log forgery. This vulnerability highlights the importance of input validation and output encoding in logging mechanisms within critical infrastructure software like Jenkins.

For European organizations, the primary impact is on the integrity of security and operational logs generated by Jenkins servers. Since Jenkins is heavily used in software development and deployment pipelines, forged log entries could mislead administrators during incident investigations or routine audits, potentially allowing attackers to hide unauthorized activities or cause confusion. This could delay detection of breaches or operational issues, increasing risk exposure. While confidentiality and availability are not directly affected, the loss of log integrity undermines trust in monitoring and forensic capabilities, which are critical for compliance with regulations such as GDPR and NIS Directive. Organizations relying on Jenkins for critical CI/CD workflows may face increased risk of undetected compromise or operational errors. The medium severity rating suggests that while the vulnerability is not immediately critical, it poses a meaningful risk that should be addressed promptly to maintain secure development environments and reliable audit trails.

To mitigate CVE-2025-59476, organizations should first upgrade Jenkins to a version where this vulnerability is patched once available. In the absence of an official patch, administrators can implement strict input validation and sanitization on any user-supplied content that may be logged, ensuring that line break characters and other control characters are either removed or properly escaped before logging. Additionally, configuring Jenkins to restrict who can submit content that appears in logs can reduce exposure. Monitoring logs for suspicious or anomalous entries that contain unexpected line breaks or formatting irregularities can help detect exploitation attempts. Employing centralized log management solutions with integrity verification and alerting on log anomalies can further enhance detection. Finally, educating administrators to be aware of this type of log forgery risk will improve incident response effectiveness.