CVE-2025-46827 is a high-severity cross-site scripting (XSS) vulnerability affecting Graylog2's graylog2-server versions prior to 6.0.14, and versions from 6.1.0 up to but not including 6.1.10. Graylog is an open-source log management platform widely used for collecting, indexing, and analyzing log data. The vulnerability arises from improper neutralization of input during web page generation (CWE-79), specifically when an attacker submits an HTML form as part of an Event Definition Remediation Step field. This malicious input can be rendered in the web interface, allowing an attacker to steal user session cookies. For exploitation, the attacker must have a user account with permissions to create event definitions, while the victim user must have permissions to view alerts. Additionally, the Graylog server must have an active input capable of receiving form data, such as HTTP input, TCP raw, or syslog inputs. The attack requires user interaction (the victim viewing the alert) and privileges to create event definitions, which limits the attack surface but does not eliminate risk. Successful exploitation can lead to full compromise of user sessions, enabling unauthorized access to the Graylog interface with the victim's privileges. The vulnerability has a CVSS 3.1 score of 8.0, reflecting high impact on confidentiality, integrity, and availability, with network attack vector, low attack complexity, and requiring privileges and user interaction. Fixed versions include 6.0.14, 6.1.10, and 6.2.0. No known workarounds exist, making patching critical. No known exploits are currently in the wild, but the presence of the vulnerability in widely deployed logging infrastructure poses a significant risk if weaponized.

For European organizations, this vulnerability poses a significant risk to the security and integrity of log management systems. Graylog servers often contain sensitive operational and security logs, which if accessed or manipulated by attackers, could lead to data breaches, disruption of incident response, and loss of forensic evidence. The ability to hijack user sessions could allow attackers to escalate privileges within the Graylog environment, potentially accessing or altering logs, creating false alerts, or disabling monitoring capabilities. This undermines trust in security monitoring and could facilitate further attacks. Given the reliance on centralized logging for compliance with regulations such as GDPR and NIS Directive, exploitation could lead to regulatory non-compliance and associated penalties. The requirement for attacker privileges to create event definitions and the need for victim user interaction somewhat limit the scope, but insider threats or compromised accounts could easily exploit this. The lack of workarounds means European organizations must prioritize patching to maintain operational security and compliance.

1. Immediate upgrade of graylog2-server to versions 6.0.14, 6.1.10, or later (6.2.0+) to apply the official fix. 2. Restrict permissions tightly: limit the ability to create event definitions to only trusted administrators and reduce the number of users who can view alerts to minimize attack vectors. 3. Monitor and audit user accounts with event definition creation privileges for suspicious activity. 4. Disable or restrict inputs capable of receiving form data (HTTP, TCP raw, syslog) if not strictly necessary, to reduce the attack surface. 5. Implement web application firewall (WAF) rules to detect and block suspicious HTML form submissions in remediation steps, if feasible. 6. Educate users with alert viewing permissions about the risk of interacting with suspicious alerts or content. 7. Regularly review Graylog logs for anomalous event definition creations or alert views that could indicate exploitation attempts. 8. Incorporate this vulnerability into vulnerability management and incident response plans to ensure rapid detection and remediation.