CVE-2012-0338 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 SSH connections from arbitrary source IP addresses via a standard SSH client, aka Bug ID CSCsv86113.
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Analysis
by VulDB Data Team • 05/09/2018
The vulnerability described in CVE-2012-0338 represents a significant security flaw in Cisco IOS software versions 12.2 through 12.4 and 15.0, specifically affecting the enforcement of access-class commands within virtual routing and forwarding (VRF) contexts. This issue stems from the software's failure to properly recognize the vrf-also keyword when processing access control lists, creating an unintended bypass mechanism that undermines network security controls. The vulnerability is particularly concerning because it affects a fundamental network security feature that should restrict remote access based on source IP addresses, yet allows unauthorized connections to be established through SSH protocols.
The technical implementation of this flaw occurs at the access control enforcement layer within Cisco IOS where the system should validate VRF contexts against access-class configurations. When the vrf-also keyword is present in access-list definitions, the IOS software fails to properly interpret this directive during SSH connection establishment, resulting in access control decisions that bypass VRF-specific restrictions. This misconfiguration allows attackers to establish SSH sessions from any source IP address, regardless of the access-list rules that should normally restrict such connections. The vulnerability operates at the network protocol level, specifically impacting the SSH daemon's authentication process and access control decision-making mechanisms.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it fundamentally compromises the network segmentation capabilities that VRF technology is designed to provide. Attackers can exploit this flaw to bypass network access controls and establish secure shell connections from arbitrary locations, potentially gaining administrative access to network devices. This represents a critical escalation from the expected behavior of access-class commands, which should enforce source IP restrictions within specific VRF contexts. The vulnerability affects network infrastructure devices that rely on IOS for access control enforcement, potentially allowing attackers to move laterally within networks where VRF-based segmentation is implemented for security isolation.
Mitigation strategies for CVE-2012-0338 should prioritize immediate software patching to address the IOS software flaw, as Cisco has released security advisories and patches specifically targeting this vulnerability. Network administrators should implement additional access control measures such as configuring SSH access lists that explicitly restrict connections based on source IP addresses, regardless of VRF configuration. The implementation of network segmentation controls using multiple VRF instances with proper access control enforcement should be reviewed and strengthened to prevent unauthorized access. Organizations should also consider implementing network monitoring and anomaly detection systems to identify unauthorized SSH connection attempts that may indicate exploitation of this vulnerability. This issue aligns with CWE-284 Access Control Flaws and relates to ATT&CK technique T1021.004 Remote Services SSH, emphasizing the critical need for proper access control enforcement in network infrastructure devices.
The vulnerability demonstrates the complexity of access control enforcement in multi-VRF environments where keyword recognition and interpretation play crucial roles in security policy enforcement. It highlights the importance of proper software validation and testing of access control mechanisms, particularly in enterprise network infrastructure where segmentation and access control are fundamental security requirements. Organizations should conduct thorough vulnerability assessments of their IOS-based network devices to identify similar issues and ensure proper access control enforcement across all network segments. This vulnerability underscores the necessity of maintaining up-to-date security patches and implementing comprehensive network security monitoring to detect and respond to exploitation attempts effectively.