CVE-2023-32725: Zabbix Server Auth Bypass Vulnerability

CVE-2023-32725 Overview

CVE-2023-32725 is a session hijacking vulnerability in Zabbix monitoring software that affects the URL widget functionality used in dashboards. The vulnerability occurs when testing or executing scheduled reports—the website configured in the URL widget receives the user's session cookie, which can then be exploited by an attacker to gain unauthorized access to the Zabbix frontend with the privileges of the affected user.

Critical Impact

Attackers can hijack authenticated user sessions by configuring malicious URLs in widgets, potentially gaining full administrative access to Zabbix monitoring infrastructure.

Affected Products

• Zabbix Server (multiple versions including 7.0.0 alpha1, alpha2, alpha3)
• Zabbix Frontend (multiple versions including 7.0.0 alpha1, alpha2, alpha3)
• Zabbix deployments using URL widgets with scheduled reports

Discovery Timeline

• 2023-12-18 - CVE-2023-32725 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-32725

Vulnerability Analysis

This vulnerability is classified under CWE-565 (Reliance on Cookies without Validation or Integrity Checking). The core issue stems from improper handling of session cookies when the Zabbix reporting system renders URL widgets. When a user tests or schedules a report containing a URL widget, the Zabbix system makes HTTP requests to the configured external URLs while inadvertently including the user's session cookie in these requests.

The attack exploits the trust relationship between the Zabbix server and external websites configured in URL widgets. Since session cookies are transmitted without proper scope validation, any attacker-controlled server receiving these requests can capture valid session tokens. These captured cookies remain valid and can be replayed to authenticate as the victim user without requiring any additional credentials.

Root Cause

The root cause lies in the improper cookie scope handling within Zabbix's report generation and URL widget rendering functionality. When the system processes URL widgets for reports, it fails to strip or properly scope session cookies before making external HTTP requests. This design flaw allows sensitive authentication material to leak to arbitrary external domains configured by users with widget configuration privileges.

Attack Vector

The attack vector is network-based and requires user interaction. An attacker with access to configure URL widgets (or the ability to convince an administrator to add their malicious URL) can set up a data collection endpoint. When victims interact with reports containing the malicious widget—either by testing the report or when scheduled reports execute—their session cookies are transmitted to the attacker's server.

The attacker then captures these session tokens and uses them to authenticate to the Zabbix frontend, bypassing the normal authentication flow entirely. This grants the attacker the same permissions as the victim, which could include administrative access to the monitoring infrastructure.

Detection Methods for CVE-2023-32725

Indicators of Compromise

• Unusual URL widget configurations pointing to external or unknown domains
• Suspicious HTTP requests from the Zabbix server to unexpected external endpoints
• Session activity originating from IP addresses inconsistent with legitimate user access patterns
• Audit log entries showing access to sensitive configurations from unfamiliar sources

Detection Strategies

• Review URL widget configurations across all dashboards for suspicious or unauthorized external URLs
• Monitor network traffic from Zabbix servers for outbound connections to non-standard destinations
• Implement session monitoring to detect concurrent access from geographically disparate locations
• Enable comprehensive audit logging for all widget configuration changes

Monitoring Recommendations

• Configure alerts for new URL widget creations pointing to external domains
• Monitor session usage patterns for anomalies indicating potential session hijacking
• Track report generation activities and correlate with outbound network connections
• Implement network-level monitoring to detect cookie exfiltration attempts

How to Mitigate CVE-2023-32725

Immediate Actions Required

• Audit all existing URL widgets and remove or disable any pointing to untrusted external URLs
• Restrict URL widget configuration permissions to trusted administrators only
• Implement network-level controls to limit outbound connections from Zabbix servers
• Review access logs for any signs of session compromise and invalidate suspicious sessions

Patch Information

Zabbix has addressed this vulnerability in updated versions of the software. Organizations should upgrade to the latest patched version of Zabbix Server and Frontend. For detailed patch information and affected version ranges, refer to the Zabbix Support Issue ZBX-23854.

Workarounds

• Disable URL widgets entirely if they are not essential to operations
• Configure firewall rules to restrict outbound HTTP/HTTPS connections from Zabbix servers to approved destinations only
• Implement a proxy for all outbound Zabbix connections that strips authentication cookies from requests
• Use shorter session timeouts to limit the window of opportunity for session token reuse

# Example: Restrict outbound connections from Zabbix server using iptables
# Allow only connections to trusted monitoring endpoints
iptables -A OUTPUT -p tcp --dport 80 -d trusted-endpoint.example.com -j ACCEPT
iptables -A OUTPUT -p tcp --dport 443 -d trusted-endpoint.example.com -j ACCEPT
# Block other outbound HTTP/HTTPS from Zabbix server
iptables -A OUTPUT -p tcp --dport 80 -m owner --uid-owner zabbix -j DROP
iptables -A OUTPUT -p tcp --dport 443 -m owner --uid-owner zabbix -j DROP