CVE-2021-42583
📋 TL;DR
CVE-2021-42583 is a cryptographic vulnerability in Maddy email server software where weak or broken cryptographic algorithms could expose sensitive authentication information. This affects all Maddy installations before version 0.5.2 that use the shadow authentication module. Attackers could potentially intercept or decrypt authentication data.
💻 Affected Systems
- Maddy Mail Server
📦 What is this software?
Maddy by Foxcpp
⚠️ Risk & Real-World Impact
Worst Case
Authentication credentials could be intercepted and decrypted, leading to unauthorized access to email accounts and potential data exfiltration.
Likely Case
Attackers with network access could intercept authentication attempts and potentially recover passwords or session tokens.
If Mitigated
With proper network segmentation and monitoring, impact is limited to potential authentication data exposure without direct system compromise.
🎯 Exploit Status
Exploitation requires network access to intercept authentication traffic and cryptographic analysis capabilities.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.5.2 and later
Vendor Advisory: https://github.com/foxcpp/maddy/releases/tag/v0.5.2
Restart Required: Yes
Instructions:
1. Stop Maddy service. 2. Backup configuration. 3. Update to version 0.5.2 or later using package manager or manual installation. 4. Restart Maddy service.
🔧 Temporary Workarounds
Disable Shadow Authentication
linuxSwitch to alternative authentication backend not using vulnerable cryptographic implementation
Edit Maddy configuration to use different auth module (e.g., PAM, SQL)
Network Segmentation
linuxRestrict network access to Maddy authentication endpoints
iptables -A INPUT -p tcp --dport 143 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 143 -j DROP
🧯 If You Can't Patch
- Implement TLS/SSL encryption for all authentication traffic
- Deploy network monitoring and IDS/IPS to detect authentication interception attempts
🔍 How to Verify
Check if Vulnerable:
Check Maddy version: maddy --version or examine installed package versionCheck Version:
maddy --versionVerify Fix Applied:
Confirm version is 0.5.2 or later and verify authentication traffic is properly encrypted📡 Detection & Monitoring
Log Indicators:
- Failed authentication attempts with unusual timing
- Authentication errors in shadow module logs
Network Indicators:
- Unencrypted authentication traffic on IMAP/SMTP ports
- Suspicious network sniffing activity
SIEM Query:
source="maddy.log" AND ("authentication failed" OR "shadow verify")🔗 References
- https://github.com/foxcpp/maddy/blob/df40dce1284cd0fd0a9e8e7894029553d653d0a5/internal/auth/shadow/verify.go
- https://github.com/foxcpp/maddy/releases/tag/v0.5.2
- https://github.com/foxcpp/maddy/blob/df40dce1284cd0fd0a9e8e7894029553d653d0a5/internal/auth/shadow/verify.go
- https://github.com/foxcpp/maddy/releases/tag/v0.5.2
