CVE-2023-6841: Redhat Keycloak DOS Vulnerability

CVE-2023-6841 Overview

A denial of service vulnerability was discovered in Red Hat Keycloak where the amount of attributes per object is not limited. An attacker can exploit this weakness by sending repeated HTTP requests, causing resource exhaustion when the application responds with rows containing long attribute values. This resource exhaustion vulnerability affects the availability of identity and access management services that depend on Keycloak.

Critical Impact

Attackers can exhaust server resources through repeated HTTP requests, causing denial of service for authentication and authorization services that rely on Keycloak.

Affected Products

• Red Hat Keycloak
• Red Hat Single Sign-On 7.0

Discovery Timeline

• 2024-09-10 - CVE-2023-6841 published to NVD
• 2024-10-01 - Last updated in NVD database

Technical Details for CVE-2023-6841

Vulnerability Analysis

This vulnerability stems from a lack of proper input validation and resource limits within Keycloak's object attribute handling mechanism. The application fails to enforce a maximum limit on the number or size of attributes that can be associated with objects. When the server processes and returns data containing objects with numerous or excessively long attribute values, it consumes significant memory and CPU resources.

The attack leverages network-accessible endpoints without requiring authentication. An attacker can repeatedly send crafted HTTP requests that trigger the application to process and return objects with large attribute payloads, progressively exhausting server resources until the service becomes unresponsive.

Root Cause

The root cause is classified under CWE-231, which relates to improper handling of extra values. Keycloak's internal data structures do not impose adequate constraints on the quantity or length of attributes that can be stored and retrieved per object. This design flaw allows unbounded data accumulation, creating a condition where legitimate resource limits are easily exceeded through malicious input.

Attack Vector

The vulnerability is exploitable over the network with low attack complexity. No authentication or user interaction is required, making it accessible to remote unauthenticated attackers. The attack pattern involves:

1. Identifying Keycloak endpoints that handle object attributes
2. Sending multiple HTTP requests to create or retrieve objects with excessive attributes
3. Forcing the server to allocate memory for long attribute values during response generation
4. Repeating requests to progressively exhaust available server resources
5. Achieving denial of service when the application can no longer process legitimate requests

This resource exhaustion attack specifically impacts availability while confidentiality and integrity remain unaffected.

Detection Methods for CVE-2023-6841

Indicators of Compromise

• Abnormally high memory consumption on Keycloak application servers
• Elevated CPU utilization during HTTP request processing
• Increased response times for authentication and authorization requests
• Server logs showing repeated requests with unusually large payload sizes
• Out-of-memory errors or application crashes in Keycloak services

Detection Strategies

• Monitor HTTP request patterns for unusual volume or payload sizes targeting Keycloak endpoints
• Implement application performance monitoring (APM) to detect resource consumption anomalies
• Configure alerts for memory threshold breaches on servers hosting Keycloak
• Analyze web server access logs for repeated requests from single sources targeting attribute-related APIs
• Deploy rate limiting at the network edge to identify potential DoS attack patterns

Monitoring Recommendations

• Establish baseline metrics for normal Keycloak resource utilization and alert on deviations
• Enable verbose logging for attribute-related operations to capture suspicious activity
• Monitor connection queues and request processing times for early warning signs
• Implement network-level traffic analysis to detect volumetric attack patterns
• Configure automated scaling or circuit breakers to mitigate resource exhaustion impacts

How to Mitigate CVE-2023-6841

Immediate Actions Required

• Review the Red Hat CVE-2023-6841 Advisory for official guidance and patches
• Implement rate limiting on Keycloak endpoints to restrict request frequency from individual sources
• Configure web application firewall rules to limit request payload sizes
• Monitor Keycloak services for signs of resource exhaustion attacks
• Plan maintenance windows to apply vendor patches when available

Patch Information

Red Hat has acknowledged this vulnerability and is tracking it in Bug Report #2254714. Organizations should monitor the official Red Hat security advisories for patch availability and upgrade to fixed versions of Keycloak and Red Hat Single Sign-On when released. Consult the vendor advisory for specific version information and patch deployment instructions.

Workarounds

• Deploy a reverse proxy or load balancer with request rate limiting to throttle excessive requests
• Configure resource limits at the application server level to prevent complete exhaustion
• Implement network-level controls to restrict access to Keycloak endpoints from trusted sources only
• Enable request size limits in web server configurations to reject abnormally large payloads
• Consider deploying Keycloak behind a web application firewall with DoS protection capabilities

# Example nginx rate limiting configuration
limit_req_zone $binary_remote_addr zone=keycloak_limit:10m rate=10r/s;

server {
    location /auth/ {
        limit_req zone=keycloak_limit burst=20 nodelay;
        proxy_pass http://keycloak_backend;
    }
}