CVE-2005-1517 in Firewall Services Module
Summary
by MITRE
Unknown vulnerability in Cisco Firewall Services Module (FWSM) 2.3.1 and earlier, when using URL, FTP, or HTTPS filtering exceptions, allows certain TCP packets to bypass access control lists (ACLs).
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Analysis
by VulDB Data Team • 07/03/2019
The vulnerability identified as CVE-2005-1517 represents a critical flaw in Cisco Firewall Services Module FWSM version 2.3.1 and earlier implementations that directly impacts network security controls. This issue specifically affects the module's handling of URL, FTP, and HTTPS filtering exceptions, creating a potential bypass mechanism that undermines the fundamental purpose of access control lists. The flaw exists within the packet processing logic of the firewall module, where certain TCP packets are not properly evaluated against configured security policies during the filtering exception handling process. This vulnerability demonstrates a failure in the principle of least privilege and proper access control enforcement that forms the cornerstone of network security architectures.
The technical root cause of this vulnerability stems from inadequate validation and processing of TCP packet headers when the FWSM encounters filtering exceptions for web protocols. When the firewall encounters URL, FTP, or HTTPS traffic that should be subject to exception handling, the module fails to properly validate that these packets conform to the established access control policies before allowing them to pass through the security boundary. This creates a scenario where packets that should be inspected and potentially blocked based on ACL rules can successfully traverse the firewall without proper authorization checks. The vulnerability operates at the network layer and application layer interfaces within the firewall's packet processing pipeline, where exception handling logic does not adequately integrate with the core ACL enforcement mechanisms. This represents a classic case of insufficient input validation and access control bypass, aligning with CWE-284 for improper access control and CWE-347 for insufficient verification of data integrity.
The operational impact of this vulnerability extends beyond simple network connectivity issues, as it fundamentally compromises the security posture of any network relying on FWSM for traffic filtering. An attacker could potentially exploit this vulnerability to gain unauthorized access to protected network segments by crafting TCP packets that trigger the exception handling path while bypassing the intended access controls. This could enable man-in-the-middle attacks, data exfiltration, or lateral movement within the network environment. The vulnerability affects organizations that deploy Cisco FWSM in their security infrastructure, particularly those using URL, FTP, or HTTPS filtering as part of their security policy enforcement. The bypass occurs silently without generating audit logs or alerts, making detection extremely difficult and potentially allowing attackers to maintain persistent access. This flaw undermines the trust model of the network security infrastructure and could lead to significant data breaches or system compromise.
Organizations should implement immediate mitigations including upgrading to Cisco FWSM versions that address this vulnerability, which would typically involve applying the latest security patches and firmware updates from Cisco. Network administrators should also consider implementing additional monitoring and logging mechanisms to detect anomalous traffic patterns that might indicate exploitation attempts. The remediation process should include thorough testing of updated configurations to ensure that the fix does not introduce compatibility issues with existing network services. Security teams should conduct comprehensive vulnerability assessments of their firewall infrastructure to identify all affected devices and implement proper network segmentation to limit the potential impact of any exploitation attempts. Additionally, organizations should review and update their incident response procedures to address potential exploitation scenarios involving access control bypass mechanisms. This vulnerability highlights the critical importance of maintaining up-to-date security controls and demonstrates the potential for seemingly minor flaws in firewall implementations to create significant security risks. The issue should be prioritized in accordance with ATT&CK framework tactics related to privilege escalation and defense evasion, as it enables adversaries to bypass security controls without detection.