Overview
CVE-2025-49643 describes a vulnerability in Zabbix where an authenticated user, including the Guest user, can cause a disproportionate CPU load on the webserver. This is achieved by sending specially crafted parameters to the /imgstore.php endpoint. Successfully exploiting this vulnerability could lead to a denial of service (DoS) condition, impacting the availability of the Zabbix monitoring system.
Technical Details
The vulnerability resides within the imgstore.php file of Zabbix. It appears that the processing of image data or parameters passed to this script lacks proper input validation and sanitization. An attacker can craft malicious input that forces the webserver to consume excessive CPU resources when processing the request. Because even the Guest user has access by default, this makes the vulnerability relatively easier to exploit.
CVSS Analysis
Currently, no CVSS score has been assigned to CVE-2025-49643. This is likely due to the vulnerability being recently discovered or the analysis is still ongoing. However, considering the potential for denial of service, a CVSS score in the medium to high range is plausible, depending on the ease of exploitation and the duration of the CPU exhaustion.
Severity: N/A
CVSS Score: N/A
Possible Impact
The primary impact of CVE-2025-49643 is a potential denial-of-service (DoS) condition. Successful exploitation can lead to the following consequences:
- Webserver Unavailability: The excessive CPU load can render the Zabbix web interface unresponsive, preventing legitimate users from accessing monitoring data and managing the system.
- Monitoring Gaps: If the Zabbix webserver becomes unavailable, monitoring capabilities may be compromised, leading to gaps in data collection and delayed alerts for critical infrastructure issues.
- System Instability: In severe cases, the CPU exhaustion could impact other services running on the same server, potentially leading to broader system instability.
Mitigation and Patch Steps
To mitigate the risk posed by CVE-2025-49643, the following steps are recommended:
- Apply the Patch: The most effective solution is to apply the official patch provided by Zabbix. Check the Zabbix support portal (linked below) for the availability of a patch for your specific Zabbix version.
- Restrict Guest Access (If Possible): While patching is paramount, consider restricting or disabling guest access to the Zabbix frontend as a temporary measure. Review the necessity of guest access and, if not essential, disable it to limit the attack surface.
- Web Application Firewall (WAF) Rules: Implement WAF rules to filter malicious requests to
/imgstore.php. Look for patterns indicative of exploitation attempts, such as abnormally large parameters or suspicious character sequences. Consult your WAF vendor for specific guidance on creating effective rules. - Monitor Webserver Resources: Closely monitor CPU utilization and other resource metrics on the Zabbix webserver. Set up alerts to detect any unusual spikes in CPU usage, which could indicate an ongoing attack.
