CVE-2001-0929 in IOS
Summary
by MITRE
Cisco IOS Firewall Feature set, aka Context Based Access Control (CBAC) or Cisco Secure Integrated Software, for IOS 11.2P through 12.2T does not properly check the IP protocol type, which could allow remote attackers to bypass access control lists.
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Analysis
by VulDB Data Team • 12/15/2024
The vulnerability described in CVE-2001-0929 represents a critical flaw in Cisco IOS Firewall Feature set implementation that directly impacts network security controls. This weakness specifically affects Cisco IOS versions ranging from 11.2P through 12.2T, where the Context Based Access Control (CBAC) functionality fails to properly validate IP protocol types during packet processing. The flaw resides within the firewall's packet inspection mechanism that is designed to enforce access control policies but instead allows unauthorized traffic to bypass established security rules. This vulnerability operates at the network layer where IP protocol verification should occur, creating a potential attack vector that could be exploited by remote adversaries to circumvent security controls.
The technical implementation flaw stems from inadequate validation of IP protocol headers within the CBAC processing pipeline. When Cisco IOS processes packets through its firewall feature set, it should rigorously check the IP protocol field to ensure that only authorized protocols are permitted through the network boundary. However, the vulnerability allows certain protocol types to bypass this validation check, enabling attackers to craft packets that appear legitimate to the firewall while actually containing unauthorized traffic. This misconfiguration creates a path for malicious packets to traverse network security controls without proper inspection, effectively neutralizing the access control lists that administrators have configured to protect their network infrastructure.
The operational impact of this vulnerability extends beyond simple protocol bypass, as it fundamentally undermines the security posture of networks relying on Cisco IOS firewalls. Attackers can exploit this weakness to gain unauthorized access to network resources, potentially leading to data breaches, network infiltration, or service disruption. The remote nature of the attack means that adversaries do not need physical access to the network or direct connection to the firewall device to exploit the vulnerability. This flaw particularly affects organizations that depend on CBAC for their security model, where network administrators have configured access control lists expecting proper protocol validation. The vulnerability creates a situation where even well-configured firewalls can be bypassed, rendering security policies ineffective and potentially exposing sensitive network assets to unauthorized access.
Organizations affected by this vulnerability should implement immediate mitigations including upgrading to patched versions of Cisco IOS that properly validate IP protocol types within the CBAC feature set. The recommended approach involves applying Cisco's security advisories and patches that address the specific validation flaw in the firewall processing logic. Network administrators should also consider implementing additional monitoring and logging controls to detect unusual traffic patterns that might indicate exploitation attempts. From a cybersecurity perspective, this vulnerability aligns with CWE-20, which describes improper input validation, and represents a significant weakness in the defense-in-depth model where multiple layers of security are bypassed. The attack surface for this vulnerability can be mapped to ATT&CK technique T1071.004, which covers protocol tunneling, as attackers could potentially use this flaw to establish covert communication channels. Organizations should also review their existing access control policies and implement additional network segmentation measures to limit the potential impact should exploitation occur, while ensuring that all network devices are running supported and patched firmware versions to prevent similar vulnerabilities from being exploited in the future.