CVE-2021-21083
📋 TL;DR
This vulnerability allows unauthenticated attackers to trigger a denial-of-service condition in Adobe Experience Manager (AEM) by exploiting improper access controls. Affected systems include AEM Cloud Service and on-premise versions 6.5.7.0 and below, 6.4.8.3 and below, and 6.3.3.8 and below.
💻 Affected Systems
- Adobe Experience Manager (AEM)
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete application unavailability affecting all users and services dependent on the AEM instance
Likely Case
Service disruption causing website/content management system downtime
If Mitigated
Minimal impact with proper network segmentation and access controls
🎯 Exploit Status
The vulnerability requires no authentication and appears straightforward to exploit based on the description
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 6.5.8.0, 6.4.8.4, 6.3.3.9, and later Cloud Service updates
Vendor Advisory: https://helpx.adobe.com/security/products/experience-manager/apsb21-15.html
Restart Required: Yes
Instructions:
1. Download appropriate AEM Service Pack from Adobe Package Share 2. Install via Package Manager 3. Restart AEM instance 4. Verify successful installation
🔧 Temporary Workarounds
Network Access Restriction
linuxRestrict access to AEM instance using firewall rules or network segmentation
iptables -A INPUT -p tcp --dport 4502 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 4502 -j DROP
🧯 If You Can't Patch
- Implement strict network access controls to limit who can reach the AEM instance
- Deploy web application firewall (WAF) with DoS protection rules
🔍 How to Verify
Check if Vulnerable:
Check AEM version via CRX Package Manager or system consoleCheck Version:
curl -s http://localhost:4502/system/console/status-productinfo | grep 'Adobe Experience Manager'Verify Fix Applied:
Verify installed service pack version matches patched versions listed in APSB21-15📡 Detection & Monitoring
Log Indicators:
- Unusual spike in error logs
- Multiple unauthenticated requests to vulnerable endpoints
- Application crash/restart events
Network Indicators:
- High volume of requests from single/unauthenticated sources
- Abnormal traffic patterns to AEM ports
SIEM Query:
source="aem.logs" AND (error OR crash OR "access denied") AND src_ip NOT IN authenticated_ips