CVE-2020-5423
📋 TL;DR
CVE-2020-5423 is a denial-of-service vulnerability in Cloud Foundry's CAPI (Cloud Controller) where unauthenticated attackers can send malicious YAML files to specific endpoints, causing excessive CPU and memory consumption. This affects Cloud Foundry deployments running CAPI versions before 1.101.0, potentially disrupting cloud controller operations and impacting application management capabilities.
💻 Affected Systems
- Cloud Foundry Cloud Controller (CAPI)
📦 What is this software?
Capi Release by Cloudfoundry
Cf Deployment by Cloudfoundry
⚠️ Risk & Real-World Impact
Worst Case
Complete unavailability of the Cloud Controller, preventing application deployments, scaling, and management operations across the entire Cloud Foundry platform.
Likely Case
Degraded performance or temporary unavailability of Cloud Controller services, disrupting application lifecycle operations until the attack stops or resources are restored.
If Mitigated
Minimal impact with proper network controls and updated software, potentially causing brief performance degradation that doesn't affect core operations.
🎯 Exploit Status
Exploitation requires sending specially crafted YAML payloads to vulnerable endpoints. No authentication is required, making this easily exploitable by attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.101.0 and later
Vendor Advisory: https://www.cloudfoundry.org/blog/cve-2020-5423
Restart Required: Yes
Instructions:
1. Update Cloud Foundry deployment to CAPI version 1.101.0 or later. 2. Follow Cloud Foundry upgrade procedures for your specific deployment. 3. Restart Cloud Controller services after upgrade.
🔧 Temporary Workarounds
Network Access Restriction
allRestrict network access to Cloud Controller endpoints to trusted sources only
# Configure firewall rules to limit access to Cloud Controller API endpoints
# Example: iptables -A INPUT -p tcp --dport 9022 -s trusted_network -j ACCEPT
# Example: iptables -A INPUT -p tcp --dport 9022 -j DROP
Rate Limiting
linuxImplement rate limiting on Cloud Controller endpoints to mitigate DoS attempts
# Configure rate limiting in your load balancer or API gateway
# Example nginx: limit_req_zone $binary_remote_addr zone=ccapi:10m rate=10r/s;
# Add to location block: limit_req zone=ccapi burst=20 nodelay;
🧯 If You Can't Patch
- Implement strict network segmentation and firewall rules to limit access to Cloud Controller endpoints
- Deploy Web Application Firewall (WAF) with YAML parsing protection rules
🔍 How to Verify
Check if Vulnerable:
Check CAPI version: cf curl /v2/info and look for 'api_version' field. If version is below 1.101.0, system is vulnerable.Check Version:
cf curl /v2/info | grep -o '"api_version":"[^"]*"'Verify Fix Applied:
After patching, verify CAPI version is 1.101.0 or higher using cf curl /v2/info and test YAML parsing functionality.📡 Detection & Monitoring
Log Indicators:
- High CPU usage spikes on Cloud Controller nodes
- Excessive memory consumption by CAPI processes
- Failed YAML parsing attempts in application logs
- Unusual volume of requests to /v2/apps, /v2/spaces, or other CAPI endpoints
Network Indicators:
- Unusual traffic patterns to Cloud Controller API endpoints (typically port 9022)
- Large YAML payloads being sent to CAPI endpoints
- Requests from unexpected sources to CAPI
SIEM Query:
source="cloud-controller" AND (cpu_usage>90 OR memory_usage>90) OR (uri_path="/v2/*" AND content_type="application/yaml" AND request_size>100000)