CVE-2025-59476 is a vulnerability identified in Jenkins, an open-source automation server widely used for continuous integration and continuous delivery (CI/CD) pipelines. The affected versions include Jenkins 2.527 and earlier, as well as the Long-Term Support (LTS) version 2.516.2 and earlier. The vulnerability arises because Jenkins does not properly restrict or sanitize characters inserted into log messages from user-supplied content. Specifically, attackers who can control the content of log messages can insert line break characters followed by forged log entries. This manipulation can mislead administrators who rely on log outputs for monitoring, auditing, and troubleshooting. The forged log entries could obscure malicious activity, hide errors, or create false audit trails, thereby undermining the integrity and reliability of Jenkins logs. Although no known exploits are reported in the wild at the time of publication, the vulnerability poses a risk in environments where untrusted users or processes can influence log content. Since Jenkins is often integrated into critical software development workflows, this vulnerability could be leveraged as part of a broader attack chain to evade detection or misdirect incident response efforts. The vulnerability does not require authentication to exploit if the attacker can inject content into logs, but the exact attack vector depends on the Jenkins setup and user permissions. No CVSS score has been assigned yet, and no official patches or mitigations have been linked at the time of disclosure.

For European organizations, the impact of CVE-2025-59476 can be significant, especially for those relying heavily on Jenkins for their software development and deployment processes. The ability to forge log entries can lead to compromised audit trails, making it difficult to detect unauthorized actions or security incidents. This can delay incident response and forensic investigations, increasing the risk of prolonged undetected breaches. Additionally, misleading logs can cause administrators to overlook critical warnings or errors, potentially resulting in system misconfigurations or failures. In regulated industries common in Europe, such as finance, healthcare, and critical infrastructure, maintaining accurate logs is essential for compliance with standards like GDPR, NIS Directive, and ISO 27001. Manipulated logs could lead to non-compliance and legal repercussions. Furthermore, attackers might use this vulnerability as a stepping stone to cover tracks after exploiting other vulnerabilities, thereby increasing the overall risk posture of affected organizations.

To mitigate this vulnerability, European organizations should take several specific actions beyond generic advice: 1) Immediately review and restrict the sources of user input that can influence Jenkins log messages, limiting them to trusted users and processes. 2) Implement strict input validation and sanitization at the application or pipeline level to prevent injection of control characters such as line breaks into logs. 3) Monitor Jenkins logs for anomalies such as unexpected line breaks or suspicious log entries that could indicate tampering. 4) Employ external log aggregation and integrity verification tools that can detect and alert on log manipulation attempts. 5) Keep Jenkins installations updated and monitor the Jenkins security advisories for patches addressing this vulnerability; apply updates promptly once available. 6) Enforce the principle of least privilege for Jenkins users and agents to minimize the risk of unauthorized log manipulation. 7) Consider isolating Jenkins environments and limiting network access to reduce exposure. 8) Conduct regular security audits and penetration tests focusing on log integrity and injection vectors. These targeted measures will help reduce the risk of exploitation and maintain the reliability of Jenkins logs.