CVE-2012-0339 in IOS
Summary
by MITRE
Cisco IOS 12.2 through 12.4 and 15.0 does not recognize the vrf-also keyword during enforcement of access-class commands, which allows remote attackers to establish TELNET connections from arbitrary source IP addresses via a standard TELNET client, aka Bug ID CSCsi77774.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 05/10/2018
The vulnerability described in CVE-2012-0339 represents a critical access control flaw within Cisco IOS software versions 12.2 through 12.4 and 15.0. This issue specifically affects the implementation of access-class commands that are designed to control network access based on source IP addresses. The flaw manifests when the vrf-also keyword is not properly recognized during access control enforcement, creating a significant bypass mechanism that undermines the intended security controls.
The technical implementation of this vulnerability stems from how Cisco IOS processes access control lists when the vrf-also keyword is present in configuration. The vrf-also keyword is typically used to apply access control lists to multiple VRF (Virtual Routing and Forwarding) instances, but in the affected versions, the system fails to properly enforce access-class restrictions when this keyword is used. This creates a scenario where remote attackers can circumvent the intended access controls and establish Telnet connections from any source IP address, regardless of the configured access restrictions. The flaw essentially allows unauthorized remote access to network devices by bypassing the standard access control enforcement mechanisms.
From an operational impact perspective, this vulnerability poses a severe threat to network security infrastructure as it enables remote attackers to gain unauthorized access to network devices without proper authentication. The ability to establish Telnet connections from arbitrary source IP addresses means that attackers can potentially compromise network management systems, access sensitive network configurations, and potentially escalate privileges within the network. The vulnerability affects the fundamental security controls that network administrators rely upon to protect their infrastructure, making it particularly dangerous in enterprise and service provider environments where network access control is critical.
Network administrators should implement immediate mitigations including upgrading to Cisco IOS versions that have addressed this vulnerability, which were released as part of the security patches following the disclosure. The remediation process should involve careful planning to ensure that the upgrade does not disrupt existing network operations while also verifying that the vrf-also keyword configurations are properly implemented and tested. Additionally, organizations should consider implementing alternative access control mechanisms such as SSH instead of Telnet, implementing stronger authentication controls, and monitoring for unauthorized access attempts. The vulnerability aligns with CWE-284 which addresses improper access control, and can be mapped to ATT&CK techniques related to remote access and privilege escalation through network service exploitation. Organizations should also conduct comprehensive network audits to identify any devices running the affected IOS versions and ensure proper access control configurations are implemented across all network infrastructure components.