CVE-1999-0889 in CBOS
Summary
by MITRE
Cisco 675 routers running CBOS allow remote attackers to establish telnet sessions if an exec or superuser password has not been set.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability identified as CVE-1999-0889 represents a critical security flaw in Cisco 675 routers operating with CBOS operating system. This issue stems from insufficient authentication mechanisms within the router's telnet service implementation, creating a significant backdoor that malicious actors can exploit to gain unauthorized remote access to network infrastructure. The vulnerability specifically affects devices where administrative passwords have not been properly configured, leaving the system in a default state that lacks essential security controls.
The technical nature of this flaw resides in the router's default configuration behavior where telnet access remains enabled without requiring authentication credentials. When no exec or superuser password is set, the CBOS operating system fails to enforce proper access controls, allowing any remote user to establish a telnet session with administrative privileges. This represents a fundamental failure in the principle of least privilege and demonstrates poor default security configuration practices. The vulnerability operates at the network layer and application layer, leveraging the telnet protocol's inherent weaknesses while exploiting the router's trust model that assumes authenticated access when no password is present.
The operational impact of this vulnerability is severe and far-reaching for organizations utilizing affected Cisco 675 routers. Remote attackers can immediately gain full administrative control over the network infrastructure without requiring any specialized tools or complex exploitation techniques. This access enables malicious actors to modify router configurations, redirect network traffic, monitor communications, and potentially establish persistent access points within the network. The vulnerability effectively nullifies network security controls and provides attackers with a direct pathway to compromise the entire network infrastructure, as routers serve as critical gateways and control points for network operations.
Organizations should immediately implement mandatory password configuration policies for all router administrative interfaces, ensuring that both exec and superuser passwords are properly established. Network segmentation and access control measures should be implemented to limit telnet access to authorized administrative workstations only. Regular security audits and configuration reviews are essential to identify and remediate similar default configurations across network infrastructure. The vulnerability aligns with CWE-310 and CWE-255 categories related to cryptographic failures and weak credentials, while also mapping to ATT&CK techniques involving remote access tools and credential access. System administrators should disable unnecessary services, implement strong authentication mechanisms, and maintain comprehensive network monitoring to detect unauthorized access attempts. This vulnerability underscores the critical importance of proper initial configuration and the principle of defense in depth when securing network infrastructure components.