CVE-2026-103558 in Windows
Summary
by MITRE • 10/13/2026
Deadlock in Windows Routing and Remote Access Service (RRAS) allows an unauthorized attacker to deny service over a network.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified within the Microsoft Windows Routing and Remote Access Service, commonly referred to as RRAS, represents a critical denial of service condition stemming from a deadlock scenario. This flaw is rooted in improper synchronization mechanisms used by the service when handling concurrent requests or specific packet sequences. The RRAS component is responsible for managing network routing policies, remote access connections, and dynamic host configuration protocol services on Windows Server systems. When an attacker can trigger this race condition through crafted network traffic, the internal locks required to manage state transitions fail to release properly. This results in a permanent blockage of service threads, effectively freezing the RRAS functionality until the system is rebooted or the specific process is forcibly terminated by an administrator.
From a technical perspective, this issue aligns with CWE-833, which describes Deadlock as a condition where two or more processes are each waiting for the other to release a lock and stop interfering with the first process. In the context of RRAS, the deadlock likely occurs during the handling of complex routing table updates or authentication handshakes involving multiple threads competing for shared resources such as memory structures or database locks within the service architecture. The lack of proper timeout mechanisms or deadlocks prevention logic allows a malicious actor to exploit this synchronization failure by sending specific malformed packets that force the system into an unrecoverable waiting state without requiring any form of user interaction or authentication credentials in many configurations, depending on the exposure level of the RRAS interface.
The operational impact of this vulnerability is severe for organizations relying on Windows-based infrastructure for remote access and network routing stability. A successful exploitation leads to a complete denial of service for all users attempting to connect via Remote Access Service connections. This disruption can halt business operations that depend on secure remote connectivity, such as virtual private networks used by mobile employees or branch office interconnects. Furthermore, because the RRAS service is often integrated with other critical Windows services like Active Directory authentication proxies, the outage may cascade into broader network availability issues. The persistence of this state means that automated recovery mechanisms are typically ineffective, necessitating manual intervention to restore normal operations and potentially causing significant downtime costs for enterprise environments.
Mitigation strategies primarily involve applying the relevant security updates provided by Microsoft that address the synchronization logic within the RRAS component. Administrators should ensure that all Windows Server systems running RRAS have the latest cumulative patches installed as soon as they become available. In scenarios where immediate patching is not feasible, network-level mitigations can be employed to reduce exposure. This includes restricting access to the RRAS service ports using firewalls or intrusion prevention systems to allow only trusted IP addresses and subnets. Additionally, disabling unnecessary remote access features if they are not actively used in the environment reduces the attack surface available for triggering this deadlock condition. Continuous monitoring of system logs for signs of high CPU usage or unresponsive services associated with RRAS can also aid in early detection of attempted exploitation attempts before a full service outage occurs.