CVE-2021-26091
📋 TL;DR
This vulnerability allows unauthenticated attackers to infer parts of user authentication tokens due to a weak random number generator in FortiMail's Identity Based Encryption service. Attackers could potentially reset user credentials. Affects FortiMail versions 6.4.0-6.4.4 and 6.2.0-6.2.7.
💻 Affected Systems
- FortiMail
📦 What is this software?
Fortimail by Fortinet
⚠️ Risk & Real-World Impact
Worst Case
Attackers could reset credentials for all users, gaining unauthorized access to email accounts and potentially using them for further attacks.
Likely Case
Targeted credential resets for specific users, leading to account compromise and potential data exfiltration.
If Mitigated
Limited impact with proper network segmentation and monitoring, but still represents authentication bypass risk.
🎯 Exploit Status
Exploitation requires understanding of cryptographic weaknesses and token generation patterns. No public exploit code available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: FortiMail 6.4.5 and 6.2.8 or later
Vendor Advisory: https://fortiguard.com/advisory/FG-IR-21-031
Restart Required: No
Instructions:
1. Download latest firmware from Fortinet support portal. 2. Backup configuration. 3. Apply firmware update via web interface or CLI. 4. Verify update completed successfully.
🔧 Temporary Workarounds
Disable Identity Based Encryption Service
FortiMailTemporarily disable the vulnerable service if not required for operations
config system ibe
set status disable
end
🧯 If You Can't Patch
- Implement network segmentation to restrict access to FortiMail management interfaces
- Enable detailed logging and monitoring for authentication token generation and credential reset events
🔍 How to Verify
Check if Vulnerable:
Check FortiMail version via web interface (System > Status) or CLI command 'get system status'Check Version:
get system status | grep VersionVerify Fix Applied:
Verify version is 6.4.5+ or 6.2.8+ and check that Identity Based Encryption service uses proper cryptographic random generation📡 Detection & Monitoring
Log Indicators:
- Multiple failed authentication attempts followed by successful credential resets
- Unusual patterns in authentication token generation logs
Network Indicators:
- Unusual traffic to FortiMail IBE service ports from unexpected sources
- Multiple credential reset requests from single IP
SIEM Query:
source="fortimail" AND (event="authentication_failure" OR event="credential_reset") | stats count by src_ip