CVE-2001-0055 in CBOS
Summary
by MITRE
CBOS 2.4.1 and earlier in Cisco 600 routers allows remote attackers to cause a denial of service via a slow stream of TCP SYN packets.
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Analysis
by VulDB Data Team • 04/07/2019
The vulnerability identified as CVE-2001-0055 represents a critical denial of service flaw affecting Cisco 600 routers running CBOS 2.4.1 and earlier versions. This vulnerability specifically targets the router's TCP connection handling mechanism, creating a condition where legitimate network services can be disrupted through carefully crafted network traffic patterns. The issue stems from inadequate processing of TCP SYN packets within the router's network stack implementation, which fails to properly manage connection request sequences that are intentionally delayed or throttled by malicious actors.
The technical flaw manifests when the router's TCP stack encounters a slow stream of TCP SYN packets, which are the initial packets sent to establish a TCP connection. In normal operation, these packets should be processed efficiently and either accepted or rejected based on established connection criteria. However, the vulnerable CBOS versions lack proper rate limiting and connection queue management mechanisms that would normally prevent resource exhaustion. This weakness creates a scenario where an attacker can maintain a large number of half-open connections by sending SYN packets at a slow rate, effectively consuming the router's available connection slots and system resources.
The operational impact of this vulnerability extends beyond simple service disruption, as it can severely compromise network availability and reliability for legitimate users. When exploited, the vulnerability allows remote attackers to consume significant system resources including memory and processing power, leading to complete denial of service conditions that can affect all network services running through the affected router. Network administrators may observe degraded performance, connection timeouts, and complete loss of connectivity for services that depend on the router's TCP handling capabilities. The vulnerability is particularly dangerous because it can be exploited remotely without requiring authentication, making it a prime target for automated attack tools.
This vulnerability aligns with CWE-400, which categorizes improper handling of resource exhaustion conditions in network protocols, and relates to ATT&CK technique T1499.004 for network denial of service attacks. The flaw demonstrates a classic resource exhaustion attack pattern where attackers leverage protocol implementation weaknesses to consume system resources. Organizations should prioritize immediate patching of affected Cisco 600 routers to address this vulnerability, as the CBOS versions prior to 2.4.2 contain the necessary fixes to properly manage TCP SYN packet processing and prevent the accumulation of half-open connections. Network security teams should also implement monitoring for unusual TCP connection patterns and consider deploying rate limiting mechanisms at network boundaries to mitigate potential exploitation attempts.