CVE-2021-1630
📋 TL;DR
This CVE describes an XML External Entity (XXE) vulnerability in certain Mule runtime components that allows attackers to read arbitrary files from the server or perform server-side request forgery. Affected customers include those using CloudHub, GovCloud, Runtime Fabric, Pivotal Cloud Foundry, Private Cloud Edition, and on-premise deployments with vulnerable versions.
💻 Affected Systems
- Mule Runtime
- CloudHub
- GovCloud
- Runtime Fabric
- Pivotal Cloud Foundry
- Private Cloud Edition
📦 What is this software?
Mule by Salesforce
⚠️ Risk & Real-World Impact
Worst Case
Complete server compromise through file disclosure of sensitive data (passwords, keys, configs) leading to lateral movement and data exfiltration.
Likely Case
Unauthorized file system access to read sensitive configuration files, potentially exposing credentials and internal system information.
If Mitigated
Limited impact with proper XML parser hardening and network segmentation preventing external entity resolution.
🎯 Exploit Status
XXE vulnerabilities typically have low exploitation complexity when XML endpoints are exposed; exploitation requires sending specially crafted XML payloads.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Consult Salesforce/MuleSoft advisory for specific patched versions
Vendor Advisory: https://help.salesforce.com/articleView?id=000362693&type=1&mode=1
Restart Required: Yes
Instructions:
1. Review vendor advisory for affected versions. 2. Upgrade to patched Mule runtime version. 3. Restart affected services. 4. Validate XML processing functionality post-upgrade.
🔧 Temporary Workarounds
Disable XXE in XML parsers
allConfigure XML parsers to disable external entity processing and DTD resolution
Set XML parser properties: FEATURE_SECURE_PROCESSING=true, disallow-doctype-decl=true, external-general-entities=false, external-parameter-entities=false
Input validation and filtering
allImplement XML input validation to reject malicious payloads before processing
Implement XML schema validation or regex filtering for DOCTYPE and ENTITY declarations
🧯 If You Can't Patch
- Implement network segmentation to restrict access to XML processing endpoints
- Deploy web application firewall (WAF) with XXE protection rules
🔍 How to Verify
Check if Vulnerable:
Check Mule runtime version against vendor advisory; test XML endpoints with XXE payloads in controlled environmentCheck Version:
mule -v or check Mule runtime installation directory version filesVerify Fix Applied:
Verify upgraded version matches patched version; test XML endpoints with XXE payloads to confirm they're rejected📡 Detection & Monitoring
Log Indicators:
- XML parsing errors containing DOCTYPE or ENTITY references
- Unusual file access patterns from application processes
- Large XML payloads with external entity references
Network Indicators:
- HTTP requests with XML content containing DOCTYPE declarations
- Outbound connections from application to internal systems following XML processing
SIEM Query:
source="mule.log" AND ("DOCTYPE" OR "ENTITY" OR "SYSTEM") AND NOT "expected.xml"