CVE-2024-51504: Apache ZooKeeper Auth Bypass Vulnerability

CVE-2024-51504 Overview

CVE-2024-51504 is an Authentication Bypass by Spoofing vulnerability in the Apache ZooKeeper Admin Server's IPAuthenticationProvider component. The vulnerability stems from a weak default configuration that relies on HTTP request headers (specifically X-Forwarded-For) to determine client IP addresses for authentication purposes. An attacker can easily spoof these headers to bypass IP-based authentication controls and gain unauthorized access to the Admin Server.

When exploited, this vulnerability allows attackers to execute administrative commands such as snapshot and restore, potentially leading to information leakage or service availability issues. The vulnerability only affects deployments using IP-based authentication in the ZooKeeper Admin Server.

Critical Impact

Attackers can bypass IP-based authentication by spoofing the X-Forwarded-For HTTP header, gaining unauthorized access to execute Admin Server commands that could compromise data confidentiality and service availability.

Affected Products

• Apache ZooKeeper (versions prior to 3.9.3)
• Apache ZooKeeper Admin Server with IPAuthenticationProvider enabled
• Deployments relying on IP-based authentication via HTTP headers

Discovery Timeline

• 2024-11-07 - CVE CVE-2024-51504 published to NVD
• 2025-06-24 - Last updated in NVD database

Technical Details for CVE-2024-51504

Vulnerability Analysis

This vulnerability is classified as CWE-290 (Authentication Bypass by Spoofing). The root issue lies in how the IPAuthenticationProvider determines the source IP address of incoming requests. By default, the provider trusts the X-Forwarded-For HTTP header to identify the client's IP address. This header is typically set by proxy servers to preserve the original client IP when forwarding requests.

However, this header can be arbitrarily set by any client making a direct connection to the server. An attacker who knows or can guess an IP address on the allowlist can simply include that address in the X-Forwarded-For header of their request, effectively impersonating an authorized client.

The attack is network-accessible and requires no authentication or user interaction to exploit. Successful exploitation enables an attacker to execute privileged Admin Server commands, including snapshot and restore operations, which could lead to exposure of sensitive configuration data or disruption of ZooKeeper cluster availability.

Root Cause

The root cause is the insecure default configuration of the IPAuthenticationProvider that blindly trusts the X-Forwarded-For HTTP header for client IP identification. This design flaw assumes the Admin Server is always deployed behind a trusted proxy that properly sanitizes or overwrites this header, which is not always the case in production environments.

Attack Vector

The attack vector exploits the trust relationship between the Admin Server and HTTP request headers. An attacker sends a request directly to the ZooKeeper Admin Server with a spoofed X-Forwarded-For header containing an IP address that is authorized in the IPAuthenticationProvider configuration.

For example, if the Admin Server is configured to allow access from 192.168.1.100, an attacker from any IP address can craft a request with the header X-Forwarded-For: 192.168.1.100 to bypass the IP-based access control. The Admin Server will trust this header value and grant access to administrative functions.

The attack requires knowledge of at least one authorized IP address, which could be obtained through reconnaissance, information disclosure, or by targeting common internal network ranges. Once authenticated, the attacker can execute commands like snapshot to extract cluster state data or restore to potentially disrupt service availability.

Detection Methods for CVE-2024-51504

Indicators of Compromise

• Unusual requests to ZooKeeper Admin Server endpoints from external IP addresses
• Presence of X-Forwarded-For headers in direct connections (not through proxy)
• Multiple authentication attempts with varying X-Forwarded-For header values
• Unexpected snapshot or restore command executions in Admin Server logs

Detection Strategies

• Monitor HTTP access logs for requests containing X-Forwarded-For headers that don't match your proxy infrastructure
• Implement anomaly detection for Admin Server command execution patterns
• Review authentication logs for successful authentications from unexpected source IPs
• Deploy network-level monitoring to detect direct connections to Admin Server ports bypassing proxy infrastructure

Monitoring Recommendations

• Enable verbose logging on the ZooKeeper Admin Server to capture all incoming request headers
• Set up alerts for administrative command executions during non-maintenance windows
• Monitor for discrepancies between actual source IP and X-Forwarded-For header values
• Implement rate limiting and alerting on Admin Server endpoints to detect enumeration attempts

How to Mitigate CVE-2024-51504

Immediate Actions Required

• Upgrade Apache ZooKeeper to version 3.9.3 or later, which fixes this vulnerability
• Review and audit current IPAuthenticationProvider configurations
• If upgrade is not immediately possible, implement network-level access controls (firewall rules) to restrict Admin Server access
• Consider switching to stronger authentication mechanisms instead of IP-based authentication

Patch Information

Apache has released version 3.9.3 which addresses this vulnerability. Users are strongly recommended to upgrade to this version or later. For detailed information, refer to the Apache Mailing List Thread and the OpenWall OSS Security Update.

Workarounds

• Disable the Admin Server entirely if not required for operations
• Implement network-level access controls using firewalls or security groups to restrict access to trusted IP addresses at the network layer
• Deploy the Admin Server behind a reverse proxy that properly sanitizes or removes client-provided X-Forwarded-For headers before forwarding
• Configure the Admin Server to bind only to localhost if remote access is not needed
• Use alternative authentication mechanisms that do not rely on IP-based identification

# Configuration example - Disable Admin Server if not needed
# Add to zoo.cfg configuration file
admin.enableServer=false

# Alternative: Bind Admin Server to localhost only
admin.serverAddress=127.0.0.1