CVE-2019-12175 in Network Security Monitor
Summary
by MITRE
In Zeek Network Security Monitor (formerly known as Bro) before 2.6.2, a NULL pointer dereference in the Kerberos (aka KRB) protocol parser leads to DoS because a case-type index is mishandled.
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Analysis
by VulDB Data Team • 11/01/2023
The vulnerability identified as CVE-2019-12175 affects Zeek Network Security Monitor version 2.6.1 and earlier, representing a critical denial of service weakness that stems from improper handling of Kerberos protocol parsing. This issue manifests as a NULL pointer dereference within the Kerberos protocol parser component, which is part of Zeek's extensive protocol analysis framework designed to monitor and analyze network traffic for security threats.
The technical flaw occurs when the Kerberos protocol parser encounters specific malformed or unexpected input data that causes a case-type index to be mishandled during protocol state transitions. This mismanagement results in the parser attempting to dereference a NULL pointer, which leads to an immediate crash of the Zeek process. The vulnerability is particularly concerning because it can be triggered through network traffic that contains specially crafted Kerberos messages, making it exploitable by remote attackers who can send malicious packets to systems running vulnerable versions of Zeek.
From an operational perspective, this vulnerability creates significant risk for network security monitoring environments that rely on Zeek for protocol analysis and threat detection. The denial of service condition effectively disables the security monitoring capabilities of affected systems, leaving network traffic unmonitored and potentially exposing the network to undetected malicious activity. The impact extends beyond simple service disruption as organizations may experience gaps in their security posture, with potential consequences for compliance requirements and incident response capabilities that depend on continuous network monitoring.
The vulnerability maps to CWE-476 which specifically addresses NULL pointer dereference conditions in software implementations, and aligns with ATT&CK technique T1498 which covers network denial of service attacks. Organizations using Zeek for network security monitoring should prioritize immediate patching to version 2.6.2 or later, which contains the necessary fixes to properly handle the Kerberos protocol parsing edge cases. Additionally, network administrators should implement monitoring for unusual traffic patterns that might indicate exploitation attempts and consider deploying additional network segmentation measures to limit the potential impact of such attacks.
The root cause analysis reveals that the issue stems from inadequate input validation within the Kerberos protocol parser's state machine implementation, where the parser fails to properly validate index values before using them to access protocol state data structures. This type of vulnerability is particularly challenging to detect during routine testing as it typically requires specific malformed input conditions that may not be part of standard test suites, making it essential for security teams to maintain updated threat intelligence and ensure timely patch deployment across all network monitoring infrastructure.
Organizations should also consider implementing network-based intrusion detection systems that can detect and alert on unusual Kerberos traffic patterns, as well as maintaining detailed monitoring of Zeek process health and system logs to quickly identify potential exploitation attempts. The fix implemented in Zeek 2.6.2 addresses the core issue by adding proper NULL pointer checks and input validation within the Kerberos parser, ensuring that malformed protocol data cannot cause the application to crash and maintain continuous network monitoring capabilities.