CVE-2001-0866 in IOS
Summary
by MITRE
Cisco 12000 with IOS 12.0 and lines card based on Engine 2 does not properly handle an outbound ACL when an input ACL is not configured on all the interfaces of a multi port line card, which could allow remote attackers to bypass the intended access controls.
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Analysis
by VulDB Data Team • 05/19/2019
The vulnerability identified as CVE-2001-0866 represents a critical access control flaw within Cisco 12000 series routers running IOS 12.0 software with Engine 2-based line cards. This issue stems from improper handling of outbound access control lists when input ACLs are absent from all interfaces of multi-port line cards, creating a significant security gap in network perimeter protection. The flaw specifically affects routers where the input access control list configuration is incomplete across all interfaces of a multi-port line card, allowing unauthorized network access that bypasses intended security policies.
This technical vulnerability manifests due to a logic error in the IOS processing of access control list enforcement mechanisms. When an input ACL is configured on some but not all interfaces of a multi-port line card, the system fails to properly enforce outbound access control rules, creating a path for remote attackers to circumvent network security controls. The flaw operates at the network layer processing level where IOS should enforce consistent access control policies across all interfaces of a line card but instead allows traffic to pass through based on incomplete ACL configurations. The issue falls under the CWE-284 access control weakness category, specifically representing improper access control implementation where the system fails to properly enforce security policies across all network interfaces.
The operational impact of this vulnerability extends beyond simple network access control bypass to potentially expose entire network segments to unauthorized access. Remote attackers can exploit this flaw to gain access to network resources that should be protected by outbound access control lists, effectively allowing them to traverse network boundaries without proper authorization. This vulnerability enables attackers to perform reconnaissance activities, establish unauthorized connections, and potentially escalate privileges within the network environment. The attack vector is particularly concerning as it requires no local access or authentication, making it exploitable by remote adversaries who can simply attempt to establish connections that should have been blocked by the configured access control policies.
The security implications of CVE-2001-0866 align with ATT&CK technique T1046 network service scanning and T1071 application layer protocol, as attackers can leverage this vulnerability to map network topology and access protected resources. The flaw essentially creates a bypass mechanism that allows attackers to circumvent network segmentation and access controls that should prevent unauthorized traffic flows. Organizations using affected Cisco 12000 series routers with Engine 2 line cards face significant risk of unauthorized network access, data exfiltration, and potential compromise of sensitive network resources. The vulnerability demonstrates a fundamental flaw in network access control enforcement where incomplete configuration on one interface affects the entire multi-port line card's security posture.
Mitigation strategies for this vulnerability require immediate implementation of proper access control list configuration across all interfaces of multi-port line cards. Network administrators must ensure that input ACLs are consistently configured on all interfaces within affected line cards to prevent the bypass condition. Cisco recommends applying the appropriate IOS software patches or upgrading to versions that address this access control flaw. Organizations should also implement network segmentation strategies and additional monitoring to detect unauthorized traffic patterns that might indicate exploitation attempts. The remediation process involves comprehensive review of access control list configurations across all network devices, particularly focusing on multi-port line card interfaces where this vulnerability can manifest. Additionally, implementing network access control solutions and regular security audits can help identify and prevent similar configuration gaps that could lead to unauthorized access.