CVE-2023-20881
📋 TL;DR
This vulnerability allows authenticated Cloud Foundry users to overwrite syslog drain credentials of other users if they know the client certificate used for that drain. This affects Cloud Foundry instances with CAPI versions 1.140-1.152.0 and loggregator-agent v7+, potentially enabling credential theft and unauthorized access to syslog data.
💻 Affected Systems
- Cloud Foundry CAPI
- Cloud Foundry loggregator-agent
📦 What is this software?
Capi Release by Cloudfoundry
Cf Deployment by Cloudfoundry
Loggregator Agent by Cloudfoundry
⚠️ Risk & Real-World Impact
Worst Case
Attackers could intercept or manipulate all syslog traffic from affected drains, potentially accessing sensitive log data, injecting malicious content, or disrupting logging operations across the platform.
Likely Case
Privileged users with knowledge of specific client certificates could overwrite credentials for targeted syslog drains, enabling unauthorized access to log data from specific applications or services.
If Mitigated
With proper certificate management and access controls, the impact is limited to authorized users who already have access to client certificates, reducing the attack surface significantly.
🎯 Exploit Status
Exploitation requires authenticated access to Cloud Foundry and knowledge of specific client certificates. The vulnerability is in the API logic rather than a simple configuration error.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: CAPI version 1.153.0 or later
Vendor Advisory: https://www.cloudfoundry.org/blog/cve-2023-20881-cas-for-syslog-drain-mtls-feature-can-be-overwritten/
Restart Required: Yes
Instructions:
1. Upgrade Cloud Foundry CAPI to version 1.153.0 or later. 2. Ensure loggregator-agent is updated if required. 3. Restart affected components. 4. Verify syslog drain configurations remain intact after upgrade.
🔧 Temporary Workarounds
Disable vulnerable syslog drain configurations
allTemporarily disable or remove syslog drains using mTLS authentication until patching can be completed.
cf delete-service <service-name>
cf unbind-service <app-name> <service-name>
Restrict certificate access
allImplement strict access controls for client certificates used in syslog drain configurations to limit potential attackers.
🧯 If You Can't Patch
- Implement network segmentation to isolate syslog traffic from untrusted users
- Enable detailed audit logging for all syslog drain configuration changes and monitor for unauthorized modifications
🔍 How to Verify
Check if Vulnerable:
Check CAPI version with: cf api --version. If version is between 1.140 and 1.152.0 and loggregator-agent is v7+, the system is vulnerable.Check Version:
cf api --versionVerify Fix Applied:
After upgrade, verify CAPI version is 1.153.0 or later with: cf api --version. Test syslog drain functionality to ensure mTLS connections work properly.📡 Detection & Monitoring
Log Indicators:
- Unauthorized modifications to syslog drain configurations
- Unexpected certificate changes for syslog drains
- Failed mTLS authentication attempts for existing syslog drains
Network Indicators:
- Unusual traffic patterns to syslog endpoints
- Certificate validation failures for established syslog connections
SIEM Query:
source="cloudfoundry" AND (event_type="syslog_drain_update" OR event_type="certificate_change") AND user NOT IN [authorized_users]