CVE-2023-40577
📋 TL;DR
This cross-site scripting (XSS) vulnerability in Prometheus Alertmanager allows attackers with POST permission to the /api/v1/alerts endpoint to inject malicious JavaScript that executes in users' browsers. Organizations running Alertmanager versions before 0.2.51 are affected, particularly those with exposed web interfaces.
💻 Affected Systems
- Prometheus Alertmanager
📦 What is this software?
Alertmanager by Prometheus
⚠️ Risk & Real-World Impact
Worst Case
Attackers could steal session cookies, redirect users to malicious sites, perform actions as authenticated users, or deploy ransomware through browser-based attacks.
Likely Case
Session hijacking, credential theft, and unauthorized actions performed in the context of authenticated Alertmanager users.
If Mitigated
Limited impact with proper input validation and output encoding, though some risk remains if attackers can bypass controls.
🎯 Exploit Status
Exploitation requires POST permissions to the alerts endpoint but uses standard XSS techniques that are well-understood.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.2.51
Vendor Advisory: https://github.com/prometheus/alertmanager/security/advisories/GHSA-v86x-5fm3-5p7j
Restart Required: Yes
Instructions:
1. Backup current configuration. 2. Stop Alertmanager service. 3. Update to version 0.2.51 or later. 4. Restart Alertmanager service. 5. Verify functionality.
🔧 Temporary Workarounds
Input Validation Filter
allImplement web application firewall or reverse proxy rules to filter malicious JavaScript in alert payloads
# Example nginx location block with XSS filtering
location /api/v1/alerts {
# Add security headers and filtering rules
add_header X-XSS-Protection "1; mode=block";
# Consider additional input validation
}
Access Restriction
linuxRestrict POST access to /api/v1/alerts endpoint to trusted sources only
# Example using firewall rules
iptables -A INPUT -p tcp --dport 9093 -s trusted_ip -j ACCEPT
iptables -A INPUT -p tcp --dport 9093 -j DROP
🧯 If You Can't Patch
- Implement strict Content Security Policy (CSP) headers to prevent JavaScript execution
- Deploy a web application firewall (WAF) with XSS protection rules in front of Alertmanager
🔍 How to Verify
Check if Vulnerable:
Check Alertmanager version: if version < 0.2.51, system is vulnerableCheck Version:
./alertmanager --versionVerify Fix Applied:
Confirm version is 0.2.51 or later and test that malicious script tags in alert payloads are properly sanitized📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to /api/v1/alerts with script tags or JavaScript content
- Multiple failed alert submissions with suspicious payloads
Network Indicators:
- HTTP requests containing <script> tags or JavaScript code to Alertmanager endpoints
- Unusual traffic patterns to the alerts API
SIEM Query:
source="alertmanager" AND (url="/api/v1/alerts" AND method="POST" AND (body="*<script>*" OR body="*javascript:*"))