CVE-2000-0899 in Small HTTP Server
Summary
by MITRE
Small HTTP Server 2.01 allows remote attackers to cause a denial of service by connecting to the server and sending out multiple GET, HEAD, or POST requests and closing the connection before the server responds to the requests.
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Analysis
by VulDB Data Team • 04/09/2019
The vulnerability identified as CVE-2000-0899 affects Small HTTP Server version 2.01, representing a classic denial of service flaw that exploits the server's handling of concurrent connections and request processing. This vulnerability resides in the server's protocol implementation where it fails to properly manage connection states when clients send requests and immediately close connections without waiting for responses. The flaw demonstrates characteristics consistent with CWE-400, which addresses unspecified denial of service conditions, and aligns with ATT&CK technique T1499.004 for network denial of service attacks. The vulnerability manifests when an attacker establishes multiple connections to the server and sends GET, HEAD, or POST requests before abruptly closing the connection, creating a scenario where the server maintains connection state information in memory without completing the request cycle.
The technical implementation of this vulnerability exploits the server's resource management mechanisms by creating a resource exhaustion condition through connection state handling. When the server receives a request and begins processing it, it allocates memory and system resources to maintain the connection state until the request is completed or timed out. However, when clients immediately close connections without proper termination sequences, the server's connection management module fails to properly clean up these resources, leading to memory leaks and eventual resource exhaustion. This behavior creates a cascading effect where the server becomes unable to accept new legitimate connections or process valid requests, effectively rendering the service unavailable to authorized users. The vulnerability is particularly concerning because it requires minimal resources from the attacker and can be executed rapidly, making it a preferred method for disrupting service availability.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential system instability and resource consumption issues that can affect overall system performance. When exploited, the vulnerability can cause the Small HTTP Server to consume excessive memory resources as connection states accumulate without proper cleanup, potentially leading to system crashes or requiring manual intervention to restore normal operations. Network administrators may observe increased system load, reduced response times, and eventual complete service unavailability. The vulnerability's impact is amplified in environments where the server handles high connection volumes or where multiple simultaneous attacks occur, as the cumulative effect of resource exhaustion can lead to broader system degradation. Organizations relying on this server for critical web services face significant risk of operational disruption and potential business impact.
Mitigation strategies for this vulnerability should focus on implementing proper connection state management and resource cleanup mechanisms within the server's protocol handling. The most effective immediate solution involves patching the server software to properly handle connection termination events and ensure that all connection states are properly cleaned up regardless of how connections are terminated. Network-level mitigations include implementing rate limiting and connection throttling mechanisms to prevent rapid connection establishment and termination patterns. Additionally, deploying intrusion detection systems that can identify and alert on unusual connection patterns may provide early warning of potential exploitation attempts. System administrators should also consider implementing connection timeout configurations that aggressively clean up stale connection states and monitor server resource utilization to detect anomalous behavior. The vulnerability highlights the importance of proper resource management in network services and underscores the necessity of implementing robust connection state handling as outlined in industry best practices for secure server implementation.