CVE-2006-4911 in Intrusion Prevention System
Summary
by MITRE
Unspecified vulnerability in Cisco IPS 5.0 before 5.0(6p2) and 5.1 before 5.1(2), when running in inline or promiscuous mode, allows remote attackers to bypass traffic inspection via a "crafted sequence of fragmented IP packets".
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Analysis
by VulDB Data Team • 01/25/2025
The vulnerability described in CVE-2006-4911 represents a critical flaw in Cisco's Intrusion Prevention System software that affects versions prior to specific patch releases. This issue specifically impacts the IPS 5.0 and 5.1 product lines when operating in either inline or promiscuous monitoring modes, creating a significant security gap in network traffic inspection capabilities. The vulnerability stems from the system's inability to properly handle fragmented IP packets, allowing malicious actors to craft specific packet sequences that evade detection mechanisms. This weakness directly undermines the fundamental purpose of intrusion prevention systems which are designed to identify and block malicious network traffic before it can compromise network resources.
The technical implementation of this vulnerability involves the improper processing of IP fragmentation within the IPS engine's packet inspection logic. When the system encounters a crafted sequence of fragmented packets, it fails to properly reassemble and analyze the complete payload, enabling attackers to bypass the security controls that would normally detect malicious content. This flaw operates at the network protocol level and specifically targets the fragmentation handling routines that are essential for proper packet inspection. The vulnerability is particularly concerning because it affects both inline and promiscuous modes, meaning that even when the IPS is not actively blocking traffic but merely monitoring it, the system remains susceptible to this attack vector. The issue demonstrates a weakness in the system's state management and packet reassembly capabilities, where the IPS engine cannot maintain proper context across fragmented packet sequences.
From an operational impact perspective, this vulnerability creates a significant risk for organizations relying on Cisco IPS for network security protection. Attackers can exploit this weakness to deliver malicious payloads that would normally be detected by the intrusion prevention system, effectively rendering the security controls ineffective for the specific attack pattern. The ability to bypass traffic inspection means that malicious activities such as port scanning, protocol exploitation, or payload delivery can occur without detection, potentially leading to unauthorized access, data exfiltration, or network compromise. This vulnerability directly impacts the CIA triad by compromising confidentiality and integrity of network communications, as the IPS fails to provide its intended protection against crafted network traffic. Organizations may experience false security confidence while simultaneously allowing malicious activity to pass through their network defenses, creating a dangerous illusion of security.
The mitigation strategy for this vulnerability requires immediate patching of affected Cisco IPS systems to versions 5.0(6p2) or 5.1(2) and later, which contain the necessary fixes for proper fragmented packet handling. Network administrators should also implement additional monitoring and alerting mechanisms to detect unusual traffic patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-129, which addresses improper handling of input that could lead to buffer overflows or other security issues, and may also relate to CWE-128, concerning improper handling of data that could lead to incorrect processing. From an ATT&CK framework perspective, this vulnerability maps to techniques involving evasion of network security controls and potentially to initial access methods that leverage network traffic manipulation. Organizations should also consider implementing network segmentation and additional security layers to reduce the impact if exploitation occurs, while ensuring that all network monitoring systems are updated to prevent similar issues in other components of their security infrastructure.