CVE-2021-26253
📋 TL;DR
This vulnerability allows attackers to bypass DUO multi-factor authentication in Splunk Enterprise, enabling unauthorized access to protected Splunk instances. It affects Splunk Enterprise versions before 8.1.6 that are configured to use DUO MFA. The vulnerability is in Splunk's implementation, not in DUO's products or services.
💻 Affected Systems
- Splunk Enterprise
📦 What is this software?
Splunk by Splunk
⚠️ Risk & Real-World Impact
Worst Case
Attackers gain full administrative access to Splunk Enterprise, allowing data exfiltration, configuration changes, or deployment of malicious apps/extensions.
Likely Case
Unauthorized users bypass MFA to access Splunk dashboards, searches, and data they shouldn't have access to.
If Mitigated
With proper network segmentation and access controls, impact is limited to the Splunk instance itself.
🎯 Exploit Status
Exploitation requires valid credentials but bypasses the MFA step. No public exploit code is known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 8.1.6 or later
Vendor Advisory: https://www.splunk.com/en_us/product-security/announcements/svd-2022-0504.html
Restart Required: Yes
Instructions:
1. Backup Splunk configuration and data. 2. Download Splunk Enterprise 8.1.6 or later from Splunk website. 3. Stop Splunk services. 4. Install the update following Splunk's upgrade documentation. 5. Restart Splunk services. 6. Verify MFA functionality.
🔧 Temporary Workarounds
Disable DUO MFA temporarily
allTemporarily disable DUO MFA authentication until patching can be completed
Edit authentication.conf to remove or comment out DUO MFA settings
Restart Splunk services
Implement network restrictions
allRestrict access to Splunk web interface to trusted IP addresses only
Configure firewall rules to limit access to Splunk web ports (8000, 8089)
🧯 If You Can't Patch
- Implement strict network segmentation to isolate Splunk instances from untrusted networks
- Enforce strong password policies and monitor for suspicious authentication attempts
🔍 How to Verify
Check if Vulnerable:
Check Splunk version and DUO MFA configuration. If version < 8.1.6 and DUO MFA is enabled, the system is vulnerable.Check Version:
splunk versionVerify Fix Applied:
Verify Splunk version is 8.1.6 or later and test DUO MFA authentication flow.📡 Detection & Monitoring
Log Indicators:
- Failed MFA attempts followed by successful logins
- Authentication logs showing MFA bypass
Network Indicators:
- Unusual authentication patterns to Splunk web interface
SIEM Query:
source="*splunk*" ("authentication" OR "login") ("bypass" OR "failed MFA" OR "MFA skipped")