CVE-2025-67835 is a denial-of-service vulnerability identified in Paessler PRTG Network Monitor versions before 25.4.114. The vulnerability arises from the Notification Contacts functionality, which allows an authenticated attacker to trigger conditions that cause the monitoring service to become unresponsive or crash, effectively denying service to legitimate users. The attack vector requires the attacker to have valid authentication credentials, implying that the attacker must be an insider or have compromised an account with sufficient privileges. The lack of a CVSS score indicates that the vulnerability is newly published and has not yet been fully evaluated. No public exploits have been reported, suggesting limited current exploitation but a potential risk if attackers develop proof-of-concept code. PRTG Network Monitor is widely used for real-time network monitoring, alerting, and reporting, making its availability critical for maintaining operational awareness and incident response. Disruption of this service can delay detection of network issues or security incidents, increasing organizational risk. The vulnerability does not appear to allow privilege escalation or data leakage but focuses on impacting service availability. The absence of patch links indicates that a fix may be forthcoming or pending deployment by Paessler. Organizations should monitor vendor advisories closely and prepare to apply updates promptly.

For European organizations, the impact of this vulnerability can be significant, especially for those relying heavily on PRTG Network Monitor for critical infrastructure monitoring and IT operations. A successful DoS attack could lead to loss of visibility into network health, delayed incident detection, and impaired response capabilities, potentially increasing downtime and operational risk. Sectors such as finance, telecommunications, energy, and government agencies, which depend on continuous network monitoring, could face increased exposure to secondary attacks or prolonged outages. The requirement for authentication limits the attack surface but does not eliminate risk, as insider threats or compromised credentials are common vectors. Additionally, disruption of monitoring services could affect compliance with regulatory requirements for network security and availability, such as GDPR mandates on operational resilience. The lack of known exploits currently reduces immediate risk but should not lead to complacency, as attackers may develop exploits once the vulnerability details are widely known.

1. Restrict access to the PRTG Network Monitor interface by enforcing strong authentication mechanisms, including multi-factor authentication (MFA), to reduce the risk of credential compromise. 2. Implement strict role-based access controls (RBAC) to limit the number of users who can modify Notification Contacts or other sensitive configurations. 3. Monitor user activity logs for unusual behavior indicative of attempted exploitation or unauthorized access. 4. Prepare to apply vendor patches immediately upon release; subscribe to Paessler security advisories to receive timely updates. 5. Consider network segmentation to isolate the PRTG server from less trusted network zones, limiting exposure. 6. Develop and test incident response plans that include scenarios involving monitoring system outages to ensure rapid recovery. 7. Regularly audit and update notification contact configurations to ensure they follow best practices and do not expose the system to unnecessary risk. 8. If possible, deploy redundant monitoring solutions or failover mechanisms to maintain visibility during potential outages.