CVE-2021-3523
📋 TL;DR
CVE-2021-3523 is a connection reuse vulnerability in 3Scale APICast that allows attackers to bypass API security restrictions when multiple APIs are hosted on the same IP address. This affects organizations using 3Scale APICast versions before 2.11.0 for API management, potentially allowing unauthorized access to protected APIs.
💻 Affected Systems
- Red Hat 3scale API Management
- 3Scale APICast
📦 What is this software?
Apicast by Redhat
⚠️ Risk & Real-World Impact
Worst Case
Attackers could bypass authentication and authorization controls for any API hosted on the same IP address, gaining unauthorized access to sensitive data or functionality.
Likely Case
Attackers could access APIs they shouldn't have permission to use, potentially exposing sensitive data or consuming API resources without authorization.
If Mitigated
With proper network segmentation and API isolation, impact would be limited to specific API instances rather than all APIs on the same host.
🎯 Exploit Status
Exploitation requires network access to the APICast instance and knowledge of multiple APIs hosted on the same IP.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.11.0 and later
Vendor Advisory: https://access.redhat.com/security/cve/cve-2021-3523
Restart Required: Yes
Instructions:
1. Update APICast to version 2.11.0 or later. 2. For Red Hat 3scale API Management, apply the latest security updates. 3. Restart APICast services after patching.
🔧 Temporary Workarounds
Host APIs on separate IP addresses
allEnsure each API is hosted on a unique IP address to prevent connection reuse between different APIs.
Network segmentation
allUse network segmentation to isolate different APIs from each other.
🧯 If You Can't Patch
- Implement strict API authentication and authorization checks at the application layer
- Monitor API access logs for unusual patterns of cross-API access
🔍 How to Verify
Check if Vulnerable:
Check APICast version: if version is below 2.11.0 and multiple APIs are hosted on the same IP, the system is vulnerable.Check Version:
apicast --versionVerify Fix Applied:
Verify APICast version is 2.11.0 or higher and test that APIs remain properly isolated when accessed from the same client.📡 Detection & Monitoring
Log Indicators:
- Multiple API calls from same source IP accessing different APIs in rapid succession
- Authentication failures followed by successful access to different API
Network Indicators:
- Unusual patterns of API requests crossing between different API endpoints from same source
SIEM Query:
source_ip:<IP> AND (api_endpoint:<API1> OR api_endpoint:<API2>) | stats count by api_endpoint