CVE-2018-20222
📋 TL;DR
CVE-2018-20222 is an XML External Entity (XXE) vulnerability in Airsonic that allows attackers to read arbitrary files from the server filesystem and potentially perform server-side request forgery. This affects all Airsonic instances before version 10.1.2 that parse XML input. The vulnerability is particularly dangerous because it can be exploited remotely without authentication.
💻 Affected Systems
- Airsonic
📦 What is this software?
Airsonic by Airsonic Project
⚠️ Risk & Real-World Impact
Worst Case
Complete server compromise through file disclosure of sensitive data (passwords, keys, configuration files) and potential remote code execution via SSRF or file upload.
Likely Case
Unauthorized reading of sensitive server files including configuration files, user data, and system files, potentially leading to credential theft and further system compromise.
If Mitigated
Limited impact if proper network segmentation, file system permissions, and input validation controls are in place, though file disclosure may still occur.
🎯 Exploit Status
XXE vulnerabilities are well-understood and easily exploitable with standard XXE payloads. No authentication required for exploitation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 10.1.2 and later (specifically fixed in 10.2.1)
Vendor Advisory: https://github.com/airsonic/airsonic/releases/tag/v10.2.1
Restart Required: Yes
Instructions:
1. Backup your Airsonic configuration and database. 2. Download Airsonic version 10.2.1 or later from GitHub releases. 3. Stop the Airsonic service. 4. Replace the existing Airsonic installation with the new version. 5. Restart the Airsonic service. 6. Verify the version is 10.1.2 or higher.
🔧 Temporary Workarounds
Disable XML External Entity Processing
allConfigure XML parsers to disable external entity resolution if possible in your deployment environment.
Set XML parser properties: FEATURE_SECURE_PROCESSING = true, DISALLOW_DOCTYPE_DECL = true
Network Segmentation
allRestrict Airsonic server network access to prevent SSRF attacks and limit file system exposure.
Configure firewall rules to restrict outbound connections from Airsonic server
🧯 If You Can't Patch
- Implement a web application firewall (WAF) with XXE protection rules to block malicious XML payloads
- Restrict file system permissions to limit what files Airsonic can access, and monitor for unusual file access patterns
🔍 How to Verify
Check if Vulnerable:
Check if Airsonic version is below 10.1.2. Test with XXE payloads targeting XML parsing endpoints.Check Version:
Check Airsonic web interface admin panel or look for version in application logs/configuration filesVerify Fix Applied:
Verify Airsonic version is 10.1.2 or higher and test that XXE payloads no longer work.📡 Detection & Monitoring
Log Indicators:
- Unusual XML parsing errors
- File access patterns to sensitive system files
- Large XML payloads in requests
Network Indicators:
- HTTP requests with XML content containing external entity declarations
- Outbound connections from Airsonic to internal systems
SIEM Query:
source="airsonic" AND (message="*DOCTYPE*" OR message="*ENTITY*" OR message="*file:*" OR message="*http:*")