CVE-2021-43761
📋 TL;DR
This stored Cross-Site Scripting (XSS) vulnerability in Adobe Experience Manager (AEM) allows attackers to inject malicious scripts into form fields, which execute in victims' browsers when they visit the compromised page. It affects AEM Cloud Service and on-premises versions 6.5.7.0 and below, 6.4.8.3 and below, and 6.3.3.8 and below. Users of these versions are at risk of session hijacking, data theft, or unauthorized actions.
💻 Affected Systems
- Adobe Experience Manager (AEM)
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
An attacker could steal admin credentials, perform unauthorized administrative actions, or deploy malware to users, leading to full system compromise.
Likely Case
Attackers hijack user sessions, steal sensitive data, or deface websites by injecting malicious scripts into vulnerable forms.
If Mitigated
With input validation and output encoding, the risk is reduced to minimal, preventing script execution and limiting impact to low-severity issues.
🎯 Exploit Status
Exploitation requires access to inject scripts into form fields, but no public proof-of-concept is known; typical XSS techniques apply.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: AEM 6.5.8.0, 6.4.8.4, 6.3.3.9, and updates for Cloud Service
Vendor Advisory: https://helpx.adobe.com/security/products/experience-manager/apsb21-103.html
Restart Required: Yes
Instructions:
1. Review the Adobe advisory for specific patch details. 2. Apply the relevant patch for your AEM version. 3. Restart the AEM instance to activate the fix. 4. Test functionality to ensure no disruptions.
🔧 Temporary Workarounds
Input Validation and Sanitization
allImplement server-side input validation and output encoding for all form fields to block malicious script injection.
Configure AEM filters or custom servlets to sanitize input; no single command applies.
Content Security Policy (CSP)
allDeploy a strict CSP header to mitigate XSS by restricting script execution sources.
Add 'Content-Security-Policy' header in web server config (e.g., Apache or Nginx).
🧯 If You Can't Patch
- Restrict access to vulnerable forms using authentication and authorization controls.
- Monitor and audit form submissions for suspicious script patterns.
🔍 How to Verify
Check if Vulnerable:
Check AEM version against affected ranges and review form fields for unsanitized input handling.Check Version:
Access AEM console or check CRX/DE to view version info; no universal command, use admin interfaces.Verify Fix Applied:
Verify the AEM version is updated to patched versions and test form fields with XSS payloads to ensure no execution.📡 Detection & Monitoring
Log Indicators:
- Unusual form submissions with script tags or JavaScript code in request logs.
Network Indicators:
- HTTP requests containing malicious scripts to form endpoints.
SIEM Query:
Example: search for 'script' or 'javascript' in URI or POST data to AEM form paths.