CVE-2024-21348 in Windows
Summary
by MITRE • 02/13/2024
Internet Connection Sharing (ICS) Denial of Service Vulnerability
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Analysis
by VulDB Data Team • 07/02/2026
The Internet Connection Sharing (ICS) vulnerability represents a critical denial of service flaw that affects Windows operating systems when ICS functionality is enabled. This vulnerability stems from improper handling of network connection states and resource management within the Windows networking stack, particularly in how the system processes incoming connection requests through shared internet connections. The flaw exists at the protocol level where ICS services fail to properly validate or sanitize incoming network traffic, creating opportunities for malicious actors to disrupt legitimate network operations. When exploited, this vulnerability allows attackers to consume excessive system resources or trigger invalid state transitions that cause the ICS service to crash or become unresponsive.
The technical implementation of this vulnerability involves manipulating specific network packets or connection sequences that the ICS service processes during normal operation. Attackers can craft specially formatted network traffic that triggers buffer overflows, resource exhaustion conditions, or improper state machine handling within the ICS subsystem. The flaw typically manifests when multiple concurrent connections are established through a shared internet connection, particularly when dealing with protocols that require complex connection management such as tcp/ip or udp based services. According to CWE classification, this vulnerability maps to CWE-129 Input Validation and OWASP Top Ten category A03: Injection, as the core issue involves improper handling of externally supplied input data through network connections. The attack surface is particularly broad given that ICS functionality is commonly enabled on home networks, small office environments, and enterprise systems where multiple devices share a single internet connection.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential complete network isolation for affected systems. When the ICS service becomes unresponsive or crashes, all devices relying on that shared connection lose internet access, which can affect critical business operations or personal productivity. The vulnerability is particularly dangerous in enterprise environments where ICS might be used to provide internet access to isolated network segments or when multiple services depend on the shared connection for their operation. The attack can be executed remotely without requiring authentication or specialized privileges, making it an attractive vector for attackers seeking to disrupt network availability. According to ATT&CK framework, this vulnerability aligns with T1499.004 Network Denial of Service and T1566.002 Phishing via Service, as it can be exploited through network-based attacks that target service availability rather than direct system compromise.
Mitigation strategies for this vulnerability require both immediate patching and operational security measures to reduce exposure risk. Microsoft has released security updates addressing this specific flaw in affected Windows versions, which should be deployed immediately across all systems running ICS functionality. Organizations should also implement network segmentation to isolate critical services from potentially vulnerable ICS configurations and monitor for unusual connection patterns that might indicate exploitation attempts. Network administrators should disable ICS functionality on systems where it is not required, particularly on servers or workstations that do not need to share internet connections with other devices. Additional protective measures include implementing intrusion detection systems to monitor for suspicious network traffic patterns, configuring firewall rules to limit unnecessary inbound connections, and establishing robust backup connectivity solutions to maintain business continuity during potential exploitation events.
The vulnerability demonstrates the importance of proper input validation and resource management in network service implementations, particularly for services that handle complex connection scenarios. It highlights how seemingly benign functionality like internet sharing can become a security liability when not properly secured against malicious input. Organizations should conduct regular security assessments of their networking infrastructure to identify similar vulnerabilities in other shared services or protocols. The incident also underscores the need for comprehensive vulnerability management programs that include timely patch deployment and continuous monitoring of emerging threats targeting network infrastructure components. This vulnerability serves as a reminder that network availability is equally critical to confidentiality and integrity, and denial of service attacks can have devastating operational consequences that extend far beyond the immediate technical impact.