CVE-2009-4501 in Zabbix
Summary
by MITRE
The zbx_get_next_field function in libs/zbxcommon/str.c in Zabbix Server before 1.6.8 allows remote attackers to cause a denial of service (crash) via a request that lacks expected separators, which triggers a NULL pointer dereference, as demonstrated using the Command keyword.
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Analysis
by VulDB Data Team • 02/02/2025
The vulnerability identified as CVE-2009-4501 represents a critical denial of service flaw within the Zabbix monitoring system's core components. This issue affects Zabbix Server versions prior to 1.6.8 and stems from improper handling of input parsing within the zbx_get_next_field function located in the libs/zbxcommon/str.c file. The vulnerability manifests when the system processes requests that lack expected separators, creating a condition where the application fails to properly validate input structure before attempting to access memory locations.
The technical implementation of this flaw involves a NULL pointer dereference scenario that occurs during the parsing of command keywords within Zabbix's communication protocols. When an attacker crafts a malformed request containing the Command keyword without proper separators, the zbx_get_next_field function attempts to process this input without adequate null checks. This results in the application attempting to dereference a NULL pointer, leading to an immediate crash of the Zabbix server process. The vulnerability is particularly concerning as it can be exploited remotely without requiring authentication, making it accessible to any attacker who can send requests to the vulnerable system.
From an operational perspective, this vulnerability creates significant risk for organizations relying on Zabbix for system monitoring and alerting. The denial of service condition effectively disables the monitoring capabilities of the affected server, potentially leaving critical infrastructure without visibility during the time when the system is most needed. The impact extends beyond simple service disruption as it can mask actual system failures or security incidents that the monitoring system would normally detect and report. Organizations may experience extended downtime while the service recovers from the crash, and the lack of monitoring during this period can compound the operational impact of other concurrent issues.
The vulnerability aligns with CWE-476, which specifically addresses NULL pointer dereference conditions in software implementations. This classification highlights the fundamental programming error where the application fails to validate pointer references before using them, a common weakness in input validation routines. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique for Network Denial of Service, as it enables an attacker to disrupt network monitoring services through crafted requests. The remote exploitation capability places this vulnerability in the T1190 category of Exploit Public-Facing Application, as it targets a service that typically operates on network-facing ports.
Mitigation strategies should focus on immediate patching of affected Zabbix Server installations to version 1.6.8 or later, where the input validation has been corrected. Organizations should also implement network-level controls to restrict access to Zabbix server components and monitor for unusual request patterns that might indicate exploitation attempts. Additional defensive measures include implementing application-level firewalls or intrusion detection systems that can identify and block malformed requests before they reach the vulnerable parsing functions. Regular security assessments of monitoring infrastructure should be conducted to identify similar input validation vulnerabilities that might exist in other system components, ensuring comprehensive protection against similar classes of attacks that could compromise system availability.