CVE-2023-2253: Red Hat OpenShift API DoS Vulnerability

CVE-2023-2253 Overview

A denial of service vulnerability was discovered in the distribution/distribution container registry project. The flaw exists in the /v2/_catalog endpoint, which accepts a query string parameter n to control the maximum number of records returned. This vulnerability allows a malicious user to submit an unreasonably large value for n, causing the allocation of a massive string array and potentially resulting in denial of service through excessive memory consumption.

Critical Impact

Authenticated attackers can trigger memory exhaustion on container registry servers by manipulating the n parameter in catalog requests, potentially causing service outages for container image distribution infrastructure.

Affected Products

• Red Hat OpenShift API for Data Protection
• Red Hat OpenShift Container Platform 4.0
• Red Hat OpenShift Developer Tools and Services

Discovery Timeline

• 2023-06-06 - CVE-2023-2253 published to NVD
• 2025-01-07 - Last updated in NVD database

Technical Details for CVE-2023-2253

Vulnerability Analysis

This vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling) and CWE-475 (Undefined Behavior for Input to API). The /v2/_catalog endpoint in the distribution/distribution project is designed to return a paginated list of repositories in a container registry. The endpoint accepts a query parameter n that specifies the maximum number of entries to return.

The vulnerability stems from insufficient validation of the n parameter value. When a request is made to the catalog endpoint with an extremely large value for n, the application attempts to pre-allocate a string array of that size before populating it with actual repository names. This can lead to massive memory allocations that exhaust available system resources.

Root Cause

The root cause is improper input validation combined with resource allocation without appropriate limits. The application fails to enforce reasonable upper bounds on the n parameter before using it to allocate memory structures. This allows attackers to specify arbitrarily large values that trigger excessive memory allocation, regardless of the actual number of repositories in the registry.

Attack Vector

The attack can be executed remotely over the network by any authenticated user with access to the container registry API. The attacker sends a crafted HTTP request to the /v2/_catalog endpoint with an extremely large n parameter value. This causes the server to attempt allocation of a correspondingly large string array, potentially exhausting available memory and causing the registry service to become unresponsive or crash.

The attack requires low privilege (authenticated access) and no user interaction, making it relatively straightforward to execute against vulnerable container registry deployments.

Detection Methods for CVE-2023-2253

Indicators of Compromise

• Unusual memory consumption spikes on container registry servers
• Repeated requests to /v2/_catalog endpoint with abnormally large n parameter values
• Service crashes or out-of-memory (OOM) errors in container registry logs
• Degraded performance or unavailability of container image pull/push operations

Detection Strategies

• Monitor HTTP request logs for /v2/_catalog requests containing unusually large n parameter values (e.g., values exceeding expected repository counts)
• Implement alerting on rapid memory consumption increases in container registry processes
• Review container registry access logs for patterns of repeated catalog enumeration requests from single sources
• Deploy web application firewall (WAF) rules to detect and block requests with excessively large numeric parameters

Monitoring Recommendations

• Configure memory usage alerts for container registry deployments to detect potential exploitation attempts
• Implement rate limiting on the /v2/_catalog endpoint to reduce the impact of repeated malicious requests
• Enable detailed logging for all registry API endpoints to facilitate forensic analysis
• Monitor for service restarts or OOM killer activity on systems hosting container registries

How to Mitigate CVE-2023-2253

Immediate Actions Required

• Apply vendor-provided patches for affected Red Hat OpenShift products as soon as available
• Implement input validation at the reverse proxy or WAF level to reject catalog requests with unreasonably large n values
• Review and restrict access to the container registry API to only authorized users and services
• Consider implementing request rate limiting on the /v2/_catalog endpoint as a defense-in-depth measure

Patch Information

Organizations should consult the Red Hat Bug Report #2189886 for patch availability and detailed remediation guidance. Debian users should refer to the Debian LTS Announcement for package updates addressing this vulnerability.

Workarounds

• Deploy a reverse proxy or WAF in front of the container registry to validate and limit the n parameter to reasonable values
• Restrict network access to the container registry API to trusted networks and services only
• Implement memory limits and automatic restart policies for container registry deployments to contain the impact of successful exploitation
• Monitor and alert on unusual API request patterns targeting the catalog endpoint

# Example nginx configuration to limit n parameter
# Add to location block handling /v2/_catalog
location /v2/_catalog {
    # Reject requests with n parameter exceeding 10000
    if ($arg_n ~ "^[0-9]{5,}$") {
        return 400;
    }
    proxy_pass http://registry_backend;
}