CVE-2021-20399

Q: What is the severity of CVE-2021-20399?

CVE-2021-20399 has a CVSS score of 9.1 (CRITICAL). This XXE vulnerability in IBM QRadar SIEM allows remote attackers to read sensitive files from the server or cause denial of service through memory exhaustion. It affects QRadar SIEM versions 7.3.0 through 7.3.3 Patch 8 and 7.4.0 through 7.4.3 GA.

9.1 CRITICAL

Denial of Service XXE

📋 TL;DR

This XXE vulnerability in IBM QRadar SIEM allows remote attackers to read sensitive files from the server or cause denial of service through memory exhaustion. It affects QRadar SIEM versions 7.3.0 through 7.3.3 Patch 8 and 7.4.0 through 7.4.3 GA.

💻 Affected Systems

Products:

IBM QRadar SIEM

Versions: 7.3.0 to 7.3.3 Patch 8 and 7.4.0 to 7.4.3 GA

Operating Systems: Linux-based QRadar appliances

Default Config Vulnerable: ⚠️ Yes

Notes: All default installations within affected version ranges are vulnerable when processing XML data.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete system compromise through sensitive file disclosure including configuration files, credentials, and internal network information, potentially leading to full environment takeover.

🟠

Likely Case

Unauthorized access to sensitive system files and configuration data, potentially exposing credentials and network information.

🟢

If Mitigated

Limited impact with proper network segmentation and XML parsing controls, though risk remains if vulnerable systems are exposed.

🌐 Internet-Facing: HIGH - Remote exploitation possible without authentication, making internet-facing instances extremely vulnerable.

🏢 Internal Only: MEDIUM - Internal attackers or compromised internal systems could exploit this vulnerability to escalate privileges.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

XXE vulnerabilities are well-understood attack vectors with readily available exploitation techniques, though no specific public exploit for this CVE has been confirmed.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Apply IBM security bulletin fixes - versions after 7.3.3 Patch 8 and 7.4.3 GA

Vendor Advisory: https://www.ibm.com/support/pages/node/6475263

Restart Required: Yes

Instructions:

1. Review IBM security advisory. 2. Apply appropriate fix pack or interim fix from IBM Fix Central. 3. Restart QRadar services as required. 4. Verify the fix by testing XML processing functionality.

🔧 Temporary Workarounds

Disable external entity processing

linux

Configure XML parsers to disable external entity resolution

Configure XML parser settings in QRadar to set features: FEATURE_SECURE_PROCESSING=true, disallow-doctype-decl=true

Network segmentation

linux

Restrict network access to QRadar management interfaces

iptables -A INPUT -p tcp --dport 443 -s trusted_networks -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP

🧯 If You Can't Patch

Implement strict network access controls to limit exposure to trusted sources only
Deploy web application firewall with XXE protection rules and monitor for exploitation attempts

🔍 How to Verify

Check if Vulnerable:

Check QRadar version via Admin > System & License Management > Hosts tab, or run: /opt/qradar/bin/myver

Check Version:

/opt/qradar/bin/myver

Verify Fix Applied:

Verify version is updated beyond vulnerable ranges and test XML processing with XXE payloads in a controlled environment

📡 Detection & Monitoring

Log Indicators:

Unusual XML parsing errors
File read attempts via XML entities
Memory exhaustion alerts

Network Indicators:

HTTP requests with XML payloads containing external entity references
Outbound connections to unexpected internal systems

SIEM Query:

SELECT * FROM events WHERE (category='WEB_APPLICATION' OR category='SYSTEM') AND (devicetype='QRadar' OR devicetype='IBM') AND (payload CONTAINS '<!ENTITY' OR payload CONTAINS 'SYSTEM' OR payload CONTAINS 'PUBLIC')

📊 Metadata

CVE ID: CVE-2021-20399

CVSS v3 Score: 9.1 (CRITICAL)

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

CWE: CWE-611

Published: July 27, 2021

Last Updated: November 21, 2024

🔗 References

https://exchange.xforce.ibmcloud.com/vulnerabilities/196073 VDB Entry,Vendor Advisory
https://www.ibm.com/support/pages/node/6475263 Patch,Vendor Advisory
https://exchange.xforce.ibmcloud.com/vulnerabilities/196073 VDB Entry,Vendor Advisory
https://www.ibm.com/support/pages/node/6475263 Patch,Vendor Advisory

📋 TL;DR

💻 Affected Systems

📦 What is this software?

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

Qradar Security Information And Event Manager by Ibm

⚠️ Risk & Real-World Impact

Worst Case

Likely Case

If Mitigated

🎯 Exploit Status

🛠️ Fix & Mitigation

✅ Official Fix

Instructions:

🔧 Temporary Workarounds

Disable external entity processing

Network segmentation

🧯 If You Can't Patch

🔍 How to Verify

Check if Vulnerable:

Check Version:

Verify Fix Applied:

📡 Detection & Monitoring

Log Indicators:

Network Indicators:

SIEM Query:

📊 Metadata

🔗 References

📤 Share & Export

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