CVE-2007-0917 in IOS
Summary
by MITRE
The Intrusion Prevention System (IPS) feature for Cisco IOS 12.4XE to 12.3T allows remote attackers to bypass IPS signatures that use regular expressions via fragmented packets.
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Analysis
by VulDB Data Team • 07/14/2019
The vulnerability described in CVE-2007-0917 represents a critical weakness in Cisco IOS implementations that affects versions 12.4XE through 12.3T. This flaw specifically targets the Intrusion Prevention System functionality, which is designed to detect and block malicious network traffic patterns. The vulnerability arises from how the system processes fragmented packets when evaluating regular expression-based signatures, creating a potential bypass mechanism that allows attackers to evade security monitoring. This issue fundamentally undermines the integrity of network security controls that depend on signature-based detection methods.
The technical root cause of this vulnerability stems from the improper handling of IP fragmentation within the IPS processing pipeline. When network packets are fragmented across multiple frames, the Cisco IOS IPS engine fails to properly reconstruct and analyze the complete packet content before applying regular expression signatures. This processing gap occurs because the system evaluates signatures on individual fragments rather than on the reassembled complete packet, enabling attackers to strategically fragment malicious payloads in ways that avoid detection. The flaw specifically affects regular expression-based signatures, which are commonly used for identifying complex attack patterns and malformed traffic. According to CWE-119, this vulnerability represents an improper restriction of operations within a recognized security boundary, while the ATT&CK framework would categorize this under T1071.004 for application layer protocol and T1566 for credential harvesting through network sniffing.
The operational impact of this vulnerability extends beyond simple bypass scenarios, as it effectively renders signature-based intrusion detection mechanisms ineffective against certain attack patterns. Remote attackers can exploit this weakness to deliver malicious payloads that would normally be detected by regular expression signatures, potentially leading to successful network infiltration, data exfiltration, or lateral movement within the compromised network. The vulnerability particularly affects environments where Cisco IOS devices serve as network security gateways, firewalls, or intrusion prevention systems, making it a significant concern for enterprise networks that rely on these devices for security enforcement. Organizations using affected Cisco IOS versions face the risk of undetected malicious traffic flowing through their networks, creating blind spots in their security monitoring capabilities.
Mitigation strategies for CVE-2007-0917 require immediate implementation of firmware updates from Cisco, specifically targeting the affected IOS versions that contain the necessary patches to properly handle fragmented packet processing. Network administrators should also implement additional monitoring and detection measures to identify potential exploitation attempts, including analyzing unusual fragmentation patterns and implementing alternative security controls such as stateful inspection or more robust signature validation mechanisms. The Cisco Security Advisory provides specific guidance for affected devices and recommends disabling IPS functionality on vulnerable systems until patches are applied. Organizations should also consider implementing network segmentation and redundant security controls to minimize the impact of potential exploitation, while maintaining detailed logging of network traffic patterns to detect anomalous behavior that might indicate attempted exploitation of this vulnerability.