CVE-2020-12100
📋 TL;DR
This vulnerability in Dovecot email server allows remote attackers to cause denial of service by sending specially crafted emails with deeply nested MIME parts. The uncontrolled recursion consumes system resources, potentially crashing the service. Organizations running vulnerable Dovecot versions for email submission, LMTP, or LDA services are affected.
💻 Affected Systems
- Dovecot
📦 What is this software?
Dovecot by Dovecot
Fedora by Fedoraproject
Fedora by Fedoraproject
Fedora by Fedoraproject
Ubuntu Linux by Canonical
Ubuntu Linux by Canonical
Ubuntu Linux by Canonical
Ubuntu Linux by Canonical
⚠️ Risk & Real-World Impact
Worst Case
Complete service outage of Dovecot email services, potentially affecting email delivery and access for all users until service is restarted.
Likely Case
Temporary service degradation or crashes requiring manual intervention to restart Dovecot processes.
If Mitigated
Minimal impact with proper monitoring and automated restart mechanisms in place.
🎯 Exploit Status
Exploitation requires sending a specially crafted email, which can be done by any sender to a vulnerable server.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.3.11.3 and later
Vendor Advisory: https://dovecot.org/security
Restart Required: Yes
Instructions:
1. Backup current configuration. 2. Stop Dovecot service. 3. Update to Dovecot 2.3.11.3 or later using package manager. 4. Verify configuration compatibility. 5. Start Dovecot service. 6. Test email functionality.
🔧 Temporary Workarounds
Rate limiting MIME processing
linuxImplement rate limiting or size restrictions on MIME processing to prevent deep recursion attacks
# Configure in dovecot.conf: protocol lmtp { mail_max_userip_connections = 10 }
# Add to dovecot.conf: service submission { process_limit = 100 }
Disable vulnerable services if not needed
linuxTemporarily disable submission, LMTP, or LDA services if they are not essential
# Comment out or remove submission, lmtp, lda protocols in dovecot.conf
# systemctl restart dovecot
🧯 If You Can't Patch
- Implement network-level filtering to block emails with excessive MIME nesting
- Deploy monitoring with automatic restart for Dovecot service crashes
🔍 How to Verify
Check if Vulnerable:
Check Dovecot version with: dovecot --version. If version is earlier than 2.3.11.3, system is vulnerable.Check Version:
dovecot --versionVerify Fix Applied:
After patching, verify version is 2.3.11.3 or later and test email processing with nested MIME messages.📡 Detection & Monitoring
Log Indicators:
- High memory usage alerts
- Dovecot process crashes/restarts
- Submission/LMTP/LDA service failures
- Stack overflow or recursion depth warnings in logs
Network Indicators:
- Unusually large emails with many MIME parts
- Multiple connection attempts to submission/LMTP ports
- Email delivery failures from specific sources
SIEM Query:
source="dovecot.log" AND ("out of memory" OR "segmentation fault" OR "recursion depth")🔗 References
- http://seclists.org/fulldisclosure/2021/Jan/18
- http://www.openwall.com/lists/oss-security/2020/08/12/1
- http://www.openwall.com/lists/oss-security/2021/01/04/3
- https://dovecot.org/security
- https://lists.debian.org/debian-lts-announce/2020/08/msg00024.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4AAX2MJEULPVSRZOBX3PNPFSYP4FM4TT/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EYZU6CHA3VMYYAUCMHSCCQKJEVEIKPQ2/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XKKAL3OMG76ZZ7CIEMQP2K6KCTD2RAKE/
- https://security.gentoo.org/glsa/202009-02
- https://usn.ubuntu.com/4456-1/
- https://usn.ubuntu.com/4456-2/
- https://www.debian.org/security/2020/dsa-4745
- http://seclists.org/fulldisclosure/2021/Jan/18
- http://www.openwall.com/lists/oss-security/2020/08/12/1
- http://www.openwall.com/lists/oss-security/2021/01/04/3
- https://dovecot.org/security
- https://lists.debian.org/debian-lts-announce/2020/08/msg00024.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4AAX2MJEULPVSRZOBX3PNPFSYP4FM4TT/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EYZU6CHA3VMYYAUCMHSCCQKJEVEIKPQ2/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XKKAL3OMG76ZZ7CIEMQP2K6KCTD2RAKE/
- https://security.gentoo.org/glsa/202009-02
- https://usn.ubuntu.com/4456-1/
- https://usn.ubuntu.com/4456-2/
- https://www.debian.org/security/2020/dsa-4745
