CVE-2020-12674
📋 TL;DR
CVE-2020-12674 is a buffer overflow vulnerability in Dovecot's authentication service where a specially crafted RPA request with zero length causes a crash due to improper length handling. This affects Dovecot email server installations, potentially causing denial of service. Organizations running vulnerable Dovecot versions are at risk.
💻 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 authentication service outage leading to email service disruption, potentially allowing DoS attacks that could be chained with other vulnerabilities.
Likely Case
Authentication service crashes causing temporary email service interruption until service restarts, affecting user login and email delivery.
If Mitigated
Minimal impact with proper network segmentation and monitoring allowing quick detection and service restoration.
🎯 Exploit Status
The vulnerability is straightforward to exploit with a specially crafted RPA request. Public advisories contain technical details that could be used to create exploits.
🛠️ 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. Update Dovecot using your distribution's package manager. 3. Restart Dovecot services. 4. Verify the update was successful.
🔧 Temporary Workarounds
Disable RPA authentication
linuxTemporarily disable RPA authentication method if not required
# Edit dovecot.conf and comment out or remove RPA auth mechanisms
# auth_mechanisms = plain login # Remove rpa if present
Network filtering
linuxBlock RPA authentication requests at network level
# Example iptables rule (adjust ports as needed)
# iptables -A INPUT -p tcp --dport 143 -m string --string "RPA" --algo bm -j DROP
🧯 If You Can't Patch
- Implement network segmentation to restrict access to Dovecot auth service
- Deploy WAF or IPS rules to detect and block malicious RPA requests
🔍 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 update, run: dovecot --version. Should show 2.3.11.3 or later. Also verify auth service is running normally.📡 Detection & Monitoring
Log Indicators:
- Auth service crashes in system logs
- Segmentation fault errors in Dovecot logs
- Unusual RPA authentication attempts
Network Indicators:
- Multiple RPA requests to auth service port
- Traffic patterns indicating DoS attempts
SIEM Query:
source="dovecot.log" AND ("segmentation fault" OR "auth service crashed" OR "RPA request")🔗 References
- http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00048.html
- http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00059.html
- 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
- https://www.openwall.com/lists/oss-security/2020/08/12/3
- http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00048.html
- http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00059.html
- 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
- https://www.openwall.com/lists/oss-security/2020/08/12/3
