CVE-2011-3263 in Zabbix
Summary
by MITRE
zabbix_agentd in Zabbix before 1.8.6 and 1.9.x before 1.9.4 allows context-dependent attackers to cause a denial of service (CPU consumption) by executing the vfs.file.cksum command for a special device, as demonstrated by the /dev/urandom device.
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Analysis
by VulDB Data Team • 11/18/2021
The vulnerability identified as CVE-2011-3263 affects Zabbix agent daemon versions prior to 1.8.6 and 1.9.4, representing a critical denial of service weakness that can be exploited through improper handling of file system operations. This issue specifically manifests when the vfs.file.cksum command is executed against special device files, particularly /dev/urandom, which can lead to excessive cpu consumption and system instability. The vulnerability stems from the agent's inability to properly handle special device files during checksum operations, creating a scenario where malicious or unauthorized users can exploit this behavior to disrupt normal system operations.
The technical flaw resides in the Zabbix agent's implementation of the vfs.file.cksum function which does not adequately validate or sanitize input parameters when processing device files. When the agent attempts to calculate a checksum for special device files like /dev/urandom, it enters into an infinite loop or consumes excessive cpu cycles due to the nature of these devices that continuously generate data. This behavior aligns with CWE-400, which catalogs weaknesses related to uncontrolled resource consumption, specifically addressing the improper handling of resource allocation and usage in system components. The vulnerability represents a classic case of insufficient input validation where the agent fails to recognize that certain file types cannot be processed in the expected manner, leading to resource exhaustion rather than proper error handling.
The operational impact of this vulnerability extends beyond simple service disruption as it can be leveraged by context-dependent attackers to perform sustained denial of service attacks against monitored systems. Attackers can exploit this weakness by crafting specific monitoring requests that target special device files, causing the zabbix_agentd process to consume 100% cpu resources and potentially leading to system unresponsiveness. This type of attack can be particularly damaging in production environments where system availability is critical, as it can go unnoticed for extended periods while consuming valuable computational resources. The vulnerability also demonstrates characteristics consistent with attack patterns found in the ATT&CK framework under the T1499 category, which covers resource hijacking techniques that can be used to disrupt system operations and consume computational resources.
Mitigation strategies for CVE-2011-3263 primarily focus on upgrading to patched versions of Zabbix agent software, specifically versions 1.8.6 and 1.9.4 or later, which contain proper input validation and error handling for device file operations. System administrators should also implement monitoring and alerting mechanisms to detect unusual cpu consumption patterns that might indicate exploitation attempts. Additional protective measures include restricting access to the zabbix agent configuration and monitoring capabilities, implementing proper access controls, and conducting regular security assessments of monitoring infrastructure. Organizations should also consider implementing network segmentation and firewall rules to limit exposure of zabbix agent services to untrusted networks, as this vulnerability can be exploited remotely if the agent is configured to accept connections from external sources. The vulnerability serves as a reminder of the importance of proper input validation and resource management in monitoring and security tools, particularly those that interact with system-level file operations and device files.