CVE-2024-23184
📋 TL;DR
This CVE describes a denial-of-service vulnerability in Dovecot email server where an attacker can send emails with an excessive number of address headers (From, To, Cc, Bcc), causing high CPU consumption and potential service disruption. The vulnerability affects Dovecot installations that process incoming emails, particularly those exposed to external email senders. Attackers can exploit this by sending specially crafted messages to consume system resources.
💻 Affected Systems
- Dovecot
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Complete service outage due to CPU exhaustion, preventing legitimate email processing and potentially affecting other services on the same host.
Likely Case
Degraded email service performance, delayed message delivery, and increased resource consumption affecting overall system stability.
If Mitigated
Minimal impact with proper header restrictions and rate limiting in place before messages reach Dovecot.
🎯 Exploit Status
No public exploits known, but crafting malicious emails with excessive headers is trivial. Attackers need only send email to target server.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check vendor advisory for specific fixed versions
Vendor Advisory: https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2024/oxdc-adv-2024-0002.json
Restart Required: Yes
Instructions:
1. Check current Dovecot version. 2. Update to patched version from official repositories. 3. Restart Dovecot service. 4. Verify fix is applied.
🔧 Temporary Workarounds
Implement MTA header restrictions
linuxConfigure mail transfer agent (Postfix, Exim, etc.) before Dovecot to limit number of address headers
# Postfix example: header_checks = regexp:/etc/postfix/header_checks
# Add regex to reject excessive headers
Rate limit incoming connections
linuxLimit number of connections or messages from single sources
# Use iptables or firewall rules
# Example: iptables -A INPUT -p tcp --dport 25 -m connlimit --connlimit-above 10 -j REJECT
🧯 If You Can't Patch
- Implement strict header filtering at the MTA level before Dovecot processes messages
- Deploy network-level protections like rate limiting and connection throttling for SMTP services
🔍 How to Verify
Check if Vulnerable:
Check Dovecot version and compare against patched versions in vendor advisoryCheck Version:
dovecot --versionVerify Fix Applied:
Test with sample emails containing multiple headers and monitor CPU usage📡 Detection & Monitoring
Log Indicators:
- Unusually high CPU usage by Dovecot processes
- Slow email processing times
- Multiple connection attempts with large messages
Network Indicators:
- Large SMTP messages with excessive headers
- Multiple connections from single sources sending emails
SIEM Query:
source="dovecot" AND (cpu_usage>90 OR process_time>10s)