CVE-2020-13942 – CVE-2020-13942 is a critical remote code execut... (How to Fix)

Q: What is the severity of CVE-2020-13942?

CVE-2020-13942 has a CVSS score of 9.8 (CRITICAL). CVE-2020-13942 is a critical remote code execution vulnerability in Apache Unomi that allows attackers to inject malicious OGNL or MVEL scripts through the /context.json public endpoint. This affects organizations running vulnerable versions of Apache Unomi, potentially allowing complete system compromise. The vulnerability was partially fixed in version 1.5.1 but required upgrading to 1.5.2 for complete protection.

📋 TL;DR

CVE-2020-13942 is a critical remote code execution vulnerability in Apache Unomi that allows attackers to inject malicious OGNL or MVEL scripts through the /context.json public endpoint. This affects organizations running vulnerable versions of Apache Unomi, potentially allowing complete system compromise. The vulnerability was partially fixed in version 1.5.1 but required upgrading to 1.5.2 for complete protection.

💻 Affected Systems

Products:

Apache Unomi

Versions: Versions before 1.5.2 (including partially fixed 1.5.1)

Operating Systems: All operating systems running Apache Unomi

Default Config Vulnerable: ⚠️ Yes

Notes: The /context.json endpoint is public by default configuration. Versions 1.5.1 attempted to fix this but introduced a new attack vector.

📦 What is this software?

Unomi by Apache

View all CVEs affecting Unomi →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete system compromise with remote code execution, allowing attackers to execute arbitrary commands, steal data, install malware, or pivot to other systems.

🟠

Likely Case

Remote code execution leading to data theft, system takeover, or deployment of ransomware/cryptominers.

🟢

If Mitigated

No impact if properly patched or if the vulnerable endpoint is blocked/restricted.

🌐 Internet-Facing: HIGH - The /context.json endpoint is public-facing by default, making internet-exposed instances immediately vulnerable to exploitation.

🏢 Internal Only: HIGH - Even internally accessible instances are vulnerable to internal attackers or compromised internal systems.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation is straightforward with public proof-of-concept available. The vulnerability requires no authentication and has a simple attack vector.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 1.5.2 or later

Vendor Advisory: http://unomi.apache.org/security/cve-2020-13942.txt

Restart Required: Yes

Instructions:

1. Download Apache Unomi version 1.5.2 or later from the official Apache website. 2. Stop the current Unomi service. 3. Backup your current installation and configuration. 4. Install the new version. 5. Restart the Unomi service. 6. Verify the upgrade was successful.

🔧 Temporary Workarounds

Block /context.json endpoint

all

Use web application firewall or reverse proxy to block access to the vulnerable /context.json endpoint

# Example nginx configuration to block the endpoint
location /context.json { deny all; }
# Example Apache configuration
<Location "/context.json">
    Require all denied
</Location>

Network segmentation

linux

Restrict network access to Unomi instances to only trusted sources

# Example iptables rule to restrict access
sudo iptables -A INPUT -p tcp --dport 8181 -s trusted_ip_range -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 8181 -j DROP

🧯 If You Can't Patch

Implement strict network access controls to limit who can reach the Unomi instance
Deploy a web application firewall with rules to detect and block OGNL/MVEL script injection attempts

🔍 How to Verify

Check if Vulnerable:

Check if Apache Unomi version is below 1.5.2 and if the /context.json endpoint is accessible

Check Version:

Check the Unomi web interface or examine the server logs for version information. For command line: grep -r "unomi.version" /path/to/unomi/installation/

Verify Fix Applied:

Verify the installed version is 1.5.2 or higher and test that script injection attempts are properly filtered

📡 Detection & Monitoring

Log Indicators:

Unusual POST requests to /context.json endpoint
OGNL or MVEL script patterns in request logs
Java exception logs related to script execution

Network Indicators:

HTTP requests containing OGNL or MVEL syntax patterns
Unusual outbound connections from Unomi server

SIEM Query:

source="unomi.logs" AND (uri_path="/context.json" AND (message="*OGNL*" OR message="*MVEL*" OR message="*script*"))

📊 Metadata

CVE ID: CVE-2020-13942

CVSS v3 Score: 9.8 (CRITICAL)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-20

Published: November 24, 2020

Last Updated: November 21, 2024

🔗 References

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