CVE-2001-1558 in Snort
Summary
by MITRE
Unknown vulnerability in IP defragmenter (frag2) in Snort before 1.8.3 allows attackers to cause a denial of service (crash).
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Analysis
by VulDB Data Team • 06/05/2018
The vulnerability identified as CVE-2001-1558 represents a critical flaw in the Snort network intrusion detection system's IP defragmentation functionality known as frag2. This vulnerability exists within the software's packet processing pipeline where it handles fragmented internet protocol packets that are reassembled for analysis. The issue specifically affects Snort versions prior to 1.8.3, making it a significant concern for organizations running older iterations of this widely deployed network security tool. The frag2 component is responsible for reconstructing fragmented IP packets that are commonly used in various network communications and attack scenarios, making it a critical subsystem for proper network monitoring and analysis.
The technical nature of this vulnerability stems from improper handling of malformed or specially crafted fragmented IP packets within the defragmentation process. When Snort encounters certain combinations of fragment headers and payload data that do not conform to standard IP fragmentation protocols, the frag2 module fails to properly validate or process these inputs. This leads to memory corruption or pointer manipulation issues that ultimately cause the Snort daemon to terminate unexpectedly. The flaw typically manifests when the system attempts to reassemble fragments with overlapping ranges, incorrect fragment offsets, or other anomalous characteristics that the frag2 component cannot properly handle without crashing. This behavior aligns with common software vulnerabilities categorized under CWE-129, which deals with insufficient validation of length fields, and CWE-125, which addresses out-of-bounds read conditions.
The operational impact of this vulnerability extends beyond simple service disruption as it creates a potential attack vector for denial of service campaigns targeting network monitoring infrastructure. Attackers can exploit this weakness by crafting specific fragmented packets designed to trigger the crash condition in Snort, effectively rendering the intrusion detection system unavailable during the time needed for system recovery and restart. This creates a window of vulnerability where network traffic can flow undetected through the compromised monitoring system, potentially allowing other attacks to go unnoticed while the system is offline. The attack surface is particularly concerning for organizations relying on Snort for network security monitoring, as the disruption can occur without any indication of malicious activity, making it difficult to distinguish between legitimate service interruptions and targeted attacks. According to ATT&CK framework category T1498, this vulnerability could be leveraged to execute denial of service attacks against network infrastructure, while also aligning with T1071 which covers application layer protocol usage that can be exploited to disrupt services.
Organizations affected by this vulnerability should immediately implement mitigations focused on updating to Snort version 1.8.3 or later, which includes patches addressing the frag2 defragmentation issues. The update process should be carefully coordinated to minimize network downtime while ensuring complete protection against this specific vulnerability. Additional defensive measures include implementing network segmentation to limit the exposure of Snort systems to potentially malicious traffic, deploying intrusion prevention systems that can detect and block malformed fragmented packets, and establishing robust monitoring procedures to quickly identify when Snort systems experience unexpected termination. Network administrators should also consider implementing redundant monitoring systems to maintain continuous visibility even when primary Snort instances are temporarily unavailable due to this vulnerability. The remediation process should include thorough testing of updated Snort configurations to ensure that the patch does not introduce compatibility issues with existing network monitoring policies or rulesets that organizations have developed over time.