CVE-2001-0288 in IOS
Summary
by MITRE
Cisco switches and routers running IOS 12.1 and earlier produce predictable TCP Initial Sequence Numbers (ISNs), which allows remote attackers to spoof or hijack TCP connections.
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Analysis
by VulDB Data Team • 11/24/2024
Cisco switches and routers running IOS version 12.1 and earlier contain a critical security flaw that stems from the predictable generation of TCP Initial Sequence Numbers. This vulnerability represents a fundamental weakness in the network infrastructure's ability to establish secure communication channels, as the predictable nature of ISNs undermines the core security mechanisms designed to prevent unauthorized access to network resources. The flaw affects the TCP/IP stack implementation within Cisco's IOS operating system, specifically in how it generates sequence numbers for new TCP connections, creating a pathway for sophisticated attackers to exploit the network's communication protocols.
The technical implementation of this vulnerability resides in the cryptographic randomness of TCP ISN generation within the IOS kernel. When a Cisco device establishes a TCP connection, it uses a predictable algorithm to generate the initial sequence number that serves as the foundation for the entire connection's sequence space. This predictable sequence generation allows remote attackers to accurately guess the next sequence number in an established connection, enabling them to inject malicious packets into the communication stream without being detected. The vulnerability is classified as a weakness in the generation of random numbers, specifically mapping to CWE-330, which addresses the use of insufficiently random values in security-critical contexts. Attackers can leverage this predictability to perform TCP session hijacking attacks, where they take control of legitimate TCP connections between hosts.
The operational impact of this vulnerability extends far beyond simple network disruption, as it provides attackers with the capability to completely compromise network communications and potentially gain unauthorized access to sensitive systems. Remote attackers can exploit this vulnerability from outside the network perimeter, making it particularly dangerous for enterprise environments where network security boundaries are often relaxed. The attack vector allows for the injection of malicious data into established connections, potentially leading to man-in-the-middle attacks, data theft, or complete network compromise. This vulnerability directly aligns with ATT&CK technique T1071.004, which covers application layer protocol: DNS, as attackers can manipulate network communications to redirect traffic or extract information. The predictable ISN generation also enables attackers to perform connection termination attacks, effectively breaking network communications and potentially causing service disruption.
The mitigation strategies for this vulnerability require immediate attention from network administrators and security teams responsible for Cisco network infrastructure. The most effective solution involves upgrading to Cisco IOS versions that implement proper random number generation for TCP ISNs, specifically versions beyond 12.1 where the vulnerability has been addressed. Organizations should also implement network segmentation and access control measures to limit the potential impact of successful exploitation attempts. Additional defensive measures include monitoring network traffic for unusual connection patterns and implementing intrusion detection systems that can identify potential TCP sequence number manipulation attempts. The vulnerability demonstrates the importance of proper cryptographic implementation in network infrastructure components and highlights the need for regular security assessments of core network protocols. Network security teams should also consider implementing TCP timestamp options and other security enhancements that make connection hijacking attacks more difficult to execute, as these additional protections complement the fundamental fix provided by proper ISN generation.