CVE-2025-59476 is a vulnerability identified in Jenkins, a widely used open-source automation server for continuous integration and continuous delivery (CI/CD). 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 and troubleshooting by injecting deceptive or misleading log entries. The underlying weakness corresponds to CWE-117, which involves improper output neutralization for logs. The CVSS v3.1 base score is 5.3 (medium severity), with the vector indicating that the attack can be performed remotely (AV:N), with low attack complexity (AC:L), no privileges required (PR:N), no user interaction needed (UI:N), and impacts integrity only (I:L) without affecting confidentiality or availability. There are no known exploits in the wild at the time of publication, and no patches have been linked yet. The vulnerability does not allow direct code execution or data disclosure but can undermine trust in log data, potentially masking other malicious activities or complicating incident response efforts.

For European organizations, this vulnerability can have significant operational and security implications. Jenkins is extensively used in software development pipelines across Europe, including in industries such as finance, manufacturing, telecommunications, and government sectors. The ability to inject forged log messages can lead to misinterpretation of system states, delayed detection of real security incidents, and erroneous forensic analysis. This undermines the integrity of audit trails, which are critical for compliance with regulations such as GDPR and NIS Directive that mandate accurate logging and incident reporting. Although the vulnerability does not directly compromise system confidentiality or availability, the indirect effects on incident response and trustworthiness of logs can increase the risk of prolonged undetected attacks or insider threats. Organizations relying heavily on Jenkins for CI/CD automation may face increased operational risk and potential regulatory scrutiny if log integrity is compromised.

To mitigate CVE-2025-59476, European organizations should implement several specific measures beyond generic patching advice: 1) Immediately review and restrict user inputs that can influence Jenkins log messages, applying input validation and sanitization to remove or encode line break characters and other control characters. 2) Implement log monitoring tools that can detect anomalous log entries, such as unexpected line breaks or suspicious patterns indicative of log injection attempts. 3) Harden Jenkins access controls to limit who can submit content that appears in logs, reducing the attack surface by enforcing the principle of least privilege. 4) Use centralized and immutable logging systems (e.g., append-only logs or external log aggregation services) to prevent tampering and facilitate reliable audit trails. 5) Stay updated with Jenkins security advisories and apply patches promptly once available. 6) Conduct regular security awareness training for administrators to recognize signs of log manipulation and maintain vigilance during log review processes. 7) Consider deploying Web Application Firewalls (WAFs) or runtime application self-protection (RASP) solutions that can detect and block malicious payloads targeting logging mechanisms.