CVE-2021-21511
📋 TL;DR
CVE-2021-21511 is an improper authorization vulnerability in Dell EMC Avamar Server web UI that allows remote low-privileged attackers to read or modify other users' backup data without proper authorization. This affects Avamar Server versions 19.3 and 19.4. Organizations using these versions for backup management are at risk of data exposure and unauthorized modifications.
💻 Affected Systems
- Dell EMC Avamar Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers gain full access to all backup data, potentially exfiltrating sensitive information, modifying or deleting critical backups, and compromising data integrity across the organization.
Likely Case
Low-privileged users or attackers who gain low-privileged access can view and modify backup data belonging to other users, leading to data breaches and unauthorized data manipulation.
If Mitigated
With proper network segmentation, access controls, and monitoring, impact is limited to authorized users within the backup management network, reducing external exploitation risk.
🎯 Exploit Status
Requires low-privileged user access to the web UI. No public exploit code has been disclosed as of the advisory date.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Update to version 19.4.1 or later
Vendor Advisory: https://www.dell.com/support/kbdoc/en-us/000182926/dsa-2021-033-dell-emc-avamar-server-improper-authorization-vulnerability
Restart Required: Yes
Instructions:
1. Download the latest Avamar Server update from Dell support portal. 2. Apply the update following Dell's documented procedures. 3. Restart the Avamar Server services as required.
🔧 Temporary Workarounds
Network Segmentation
allRestrict access to Avamar Server web UI to only authorized administrative networks
Access Control Hardening
allImplement strict role-based access controls and limit low-privileged user access to backup data
🧯 If You Can't Patch
- Implement network segmentation to isolate Avamar Server from untrusted networks
- Enhance monitoring and logging of web UI access patterns and backup data access
🔍 How to Verify
Check if Vulnerable:
Check Avamar Server version via web UI or command line. If version is 19.3.x or 19.4.x (excluding 19.4.1+), system is vulnerable.Check Version:
avmgr version (or check via Avamar Administration Console)Verify Fix Applied:
Verify Avamar Server version is 19.4.1 or later. Test authorization controls by attempting to access other users' backup data with low-privileged accounts.📡 Detection & Monitoring
Log Indicators:
- Unauthorized access attempts to backup data
- Unusual patterns of data access by low-privileged users
- Failed authorization checks in web UI logs
Network Indicators:
- Unusual web UI traffic patterns
- Access to backup data endpoints from unauthorized sources
SIEM Query:
source="avamar_logs" AND (event_type="authorization_failure" OR user_privilege="low" AND data_access="other_user")