CVE-2001-0751 in CBOS
Summary
by MITRE
Cisco switches and routers running CBOS 2.3.8 and earlier use predictable TCP Initial Sequence Numbers (ISN), which allows remote attackers to spoof or hijack TCP connections.
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Analysis
by VulDB Data Team • 11/24/2024
The vulnerability identified as CVE-2001-0751 represents a critical weakness in Cisco's Communications Operating System CBOS version 2.3.8 and earlier releases. This flaw resides in the network infrastructure devices that form the backbone of enterprise communications networks, specifically affecting Cisco switches and routers that are widely deployed in corporate and governmental environments. The vulnerability stems from the predictable nature of TCP initial sequence numbers, which are fundamental to the TCP protocol's connection establishment mechanism. These sequence numbers must be unpredictable to prevent malicious actors from exploiting them to gain unauthorized access to network connections.
The technical implementation of this vulnerability exploits the deterministic nature of how Cisco devices generate TCP initial sequence numbers. In properly secured systems, TCP ISNs should be cryptographically random to prevent attackers from predicting future sequence numbers. However, CBOS versions 2.3.8 and earlier implement a predictable algorithm for generating these numbers, making it feasible for remote attackers to calculate the next sequence number in a TCP conversation. This predictability allows for TCP connection hijacking, where an attacker can insert themselves into an established connection without proper authentication, effectively taking control of network communications.
The operational impact of this vulnerability extends beyond simple network disruption to encompass serious security implications for organizations relying on Cisco networking equipment. Attackers who successfully exploit this weakness can perform man-in-the-middle attacks, intercept sensitive communications, modify data in transit, or even completely sever network connections. The vulnerability affects the integrity and confidentiality of network communications, potentially exposing corporate data, financial information, and other sensitive assets. Given that these devices are often deployed in critical network infrastructure roles, the exploitation of this vulnerability could lead to widespread service degradation or complete network outages. The remote nature of the attack means that adversaries do not require physical access to the network equipment, making the threat particularly concerning for organizations with distributed network deployments.
Mitigation strategies for this vulnerability require immediate attention from network administrators and security teams. The most effective approach involves upgrading affected Cisco devices to CBOS versions that implement proper randomization of TCP initial sequence numbers, typically CBOS 3.0 or later releases. Network segmentation and access control measures should be implemented to limit the potential impact of successful exploitation attempts. Organizations should also consider implementing additional security controls such as TCP sequence number randomization at the operating system level, network intrusion detection systems, and monitoring for suspicious network activity patterns. This vulnerability aligns with CWE-330, which addresses the use of insufficiently random values, and maps to ATT&CK technique T1071.004 for application layer protocol usage, particularly in the context of network protocol manipulation and connection hijacking attacks. The vulnerability demonstrates the critical importance of cryptographic randomness in network security implementations and serves as a reminder of the long-term security implications of predictable number generation in network protocols.