CVE-1999-0969 in Windows
Summary
by MITRE
The Windows NT RPC service allows remote attackers to conduct a denial of service using spoofed malformed RPC packets which generate an error message that is sent to the spoofed host, potentially setting up a loop, aka Snork.
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Analysis
by VulDB Data Team • 04/17/2026
The vulnerability described in CVE-1999-0969 represents a critical denial of service weakness in the Windows NT Remote Procedure Call service that enables remote attackers to disrupt system operations through carefully crafted malformed packets. This flaw specifically targets the RPC service implementation in Windows NT systems, creating a condition where legitimate network traffic can be exploited to generate continuous error message loops. The vulnerability operates by exploiting the service's handling of RPC packets that contain malformed data, causing the system to respond with error messages that are then sent back to the originating host, potentially creating an infinite loop of error responses.
The technical mechanism behind this vulnerability involves the Windows NT RPC service's insufficient validation of incoming packet structures and content. When the service receives malformed RPC packets, it fails to properly handle the error conditions, leading to the generation of error messages that are sent back to the spoofed source address. This creates a scenario where the original attacker can send packets to a victim system, receive error responses, and potentially retransmit those responses back to the original source, establishing a feedback loop that consumes system resources and network bandwidth. The flaw essentially allows an attacker to trigger a denial of service condition without requiring authentication or elevated privileges, making it particularly dangerous for networked environments.
The operational impact of this vulnerability extends beyond simple service disruption, as it can consume significant system resources including memory, CPU cycles, and network bandwidth. The continuous loop of error messages generated by the spoofed packets can overwhelm the target system's ability to process legitimate traffic, effectively rendering the affected service unavailable to legitimate users. Network administrators may observe unusual traffic patterns, system performance degradation, and potential network congestion as the loop continues to propagate. The vulnerability is especially concerning because it can be exploited from remote locations without requiring any special access credentials, making it a preferred attack vector for network-level disruption.
This vulnerability aligns with CWE-121, which describes buffer overflow conditions, and demonstrates the broader category of input validation failures that can lead to denial of service conditions. From an ATT&CK framework perspective, this represents a network denial of service technique that falls under the T1498 category of Network Denial of Service, specifically utilizing T1498.001 for Direct Network Denial of Service. The attack pattern leverages the inherent weaknesses in Windows NT's RPC implementation to create a persistent denial of service condition, highlighting the importance of robust input validation and error handling mechanisms in network services. Organizations should implement network segmentation, firewall rules to restrict RPC traffic, and ensure timely patching of affected systems to mitigate this vulnerability. The flaw underscores the critical need for proper error handling in network services and demonstrates how seemingly minor implementation gaps can create significant security risks that can be exploited remotely.