CVE-2020-19613
📋 TL;DR
This Server-Side Request Forgery (SSRF) vulnerability in FlyCMS allows attackers to make the server send HTTP requests to arbitrary internal or external systems. Attackers can exploit this to access internal services, perform port scanning, or interact with cloud metadata APIs. Anyone running FlyCMS version 20190503 is affected.
💻 Affected Systems
- sunkaifei FlyCMS
📦 What is this software?
Flycms by Flycms Project
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of internal network services, cloud metadata theft leading to credential harvesting, or data exfiltration through internal service interactions.
Likely Case
Internal network reconnaissance, access to internal APIs or services, and potential data leakage from internal systems.
If Mitigated
Limited to external resource consumption or failed requests if proper network segmentation and input validation are implemented.
🎯 Exploit Status
Exploitation requires access to the image upload functionality, which typically requires authentication. The vulnerability is well-documented in public GitHub issues.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown specific version, but fixes are available in later commits
Vendor Advisory: https://github.com/sunkaifei/FlyCms/issues/1
Restart Required: Yes
Instructions:
1. Update to the latest version of FlyCMS from the official repository. 2. Apply input validation to restrict URL schemes and domains in the saveUrlAs function. 3. Restart the application server.
🔧 Temporary Workarounds
Input Validation Filter
allImplement URL validation to restrict allowed schemes and domains
Modify ImagesService.java to validate URLs before processing
Network Segmentation
allRestrict outbound network access from the application server
Configure firewall rules to limit outbound HTTP/HTTPS traffic
🧯 If You Can't Patch
- Disable the vulnerable image upload functionality entirely
- Implement a web application firewall (WAF) with SSRF protection rules
🔍 How to Verify
Check if Vulnerable:
Check if running FlyCMS version 20190503 and inspect the ImagesService.java file for the saveUrlAs function without proper URL validationCheck Version:
Check FlyCMS version in application configuration or admin panelVerify Fix Applied:
Test the image upload functionality with SSRF payloads to ensure they are blocked📡 Detection & Monitoring
Log Indicators:
- Unusual outbound HTTP requests from the application server
- Requests to internal IP addresses or cloud metadata endpoints
Network Indicators:
- HTTP traffic from application server to unexpected internal services
- Port scanning patterns from the application server
SIEM Query:
source_ip=application_server AND (dest_ip=169.254.169.254 OR dest_ip=10.* OR dest_ip=192.168.* OR dest_ip=172.16.*)