CVE-2000-0262 in KEN!
Summary
by MITRE
The AVM KEN! ISDN Proxy server allows remote attackers to cause a denial of service via a malformed request.
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Analysis
by VulDB Data Team • 02/02/2025
The AVM KEN ISDN Proxy server implementation which was designed to facilitate ISDN (Integrated Services Digital Network) communications and proxy services for enterprise networks. The flaw manifests when the server processes malformed requests that do not conform to expected protocol structures, leading to system instability and complete service disruption. This type of vulnerability falls under the broader category of improper input validation issues that have been consistently documented in cybersecurity literature and categorized under CWE-20 as "Improper Input Validation." The vulnerability demonstrates how network proxy servers can be susceptible to crafted malicious inputs that trigger system crashes or resource exhaustion, fundamentally undermining the availability of critical network services.
The technical implementation of this vulnerability stems from inadequate request parsing and validation mechanisms within the AVM KEN! ISDN Proxy server software. When remote attackers submit specially crafted malformed requests to the server, the proxy fails to properly sanitize or validate incoming data before processing. This lack of robust input validation allows attackers to exploit memory handling inconsistencies and buffer management flaws that exist in the server's request processing pipeline. The malformed requests typically contain unexpected data sequences, invalid protocol headers, or malformed packet structures that cause the server to either crash completely or enter an unstable state where it can no longer process legitimate requests. From an operational perspective, this vulnerability creates a significant risk for organizations relying on ISDN proxy services, as it provides an easily exploitable path for attackers to disrupt critical communication infrastructure. The vulnerability aligns with ATT&CK technique T1498 which describes "Network Denial of Service" and represents a classic example of how protocol implementation flaws can be weaponized to achieve system compromise through availability attacks.
The operational impact of CVE-2000-0262 extends beyond simple service disruption to potentially affect business continuity and network reliability for organizations using AVM KEN! ISDN Proxy servers. When exploited, this vulnerability can render entire ISDN communication pathways unusable, affecting voice, data, and fax services that depend on these proxy systems. The attack surface is particularly concerning because it requires minimal technical expertise to exploit, making it attractive to attackers seeking to disrupt network operations. Organizations may experience cascading effects as dependent services fail and network administrators struggle to identify and resolve the root cause of outages. The vulnerability also highlights the importance of proper security testing and validation of network infrastructure components, particularly those handling external communications. From a security compliance standpoint, this vulnerability would likely trigger alerts under various regulatory frameworks that require robust security controls for network infrastructure, including requirements related to system availability and resilience against known threats.
Mitigation strategies for CVE-2000-0262 should focus on immediate protective measures and long-term architectural improvements. Organizations should implement network segmentation and access controls to limit exposure of vulnerable ISDN proxy servers to untrusted networks, reducing the attack surface available to potential attackers. Network monitoring systems should be configured to detect unusual request patterns and malformed traffic that could indicate exploitation attempts. The most effective immediate solution involves applying vendor patches or updates when available, though in this case the vulnerability predates many modern patch management practices. Organizations should also consider implementing intrusion detection systems specifically configured to identify and block malformed requests targeting ISDN proxy services. For legacy systems where patching is not feasible, network administrators should deploy firewalls with deep packet inspection capabilities to filter out suspicious traffic patterns. Additionally, implementing redundant proxy services and failover mechanisms can help maintain availability during exploitation attempts, though this approach does not prevent the underlying vulnerability from being exploited. The vulnerability serves as a historical example of why continuous security assessment and proper input validation should be integral components of all network infrastructure development processes.