CVE-2020-25710
📋 TL;DR
CVE-2020-25710 is an assertion failure vulnerability in OpenLDAP's csnNormalize23() function that allows remote attackers to crash the LDAP service by sending specially crafted packets. This affects OpenLDAP servers before version 2.4.56, potentially causing denial of service. Organizations using vulnerable OpenLDAP installations for directory services are affected.
💻 Affected Systems
- OpenLDAP
📦 What is this software?
Fedora by Fedoraproject
Jboss Enterprise Application Platform by Redhat
View all CVEs affecting Jboss Enterprise Application Platform →
Openldap by Openldap
⚠️ Risk & Real-World Impact
Worst Case
Complete LDAP service outage leading to authentication failures, directory lookup failures, and disruption of dependent services like authentication systems, email servers, or VPNs.
Likely Case
LDAP service crash requiring manual restart, causing temporary authentication and directory service disruption for users and applications.
If Mitigated
Minimal impact with proper network segmentation and monitoring allowing quick detection and restart of affected services.
🎯 Exploit Status
The vulnerability requires sending a malicious packet to trigger the assertion failure. While no public PoC exists, the technical details are available in the commit fixing the issue.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: OpenLDAP 2.4.56 and later
Vendor Advisory: https://git.openldap.org/openldap/openldap/-/commit/ab3915154e69920d480205b4bf5ccb2b391a0a1f
Restart Required: Yes
Instructions:
1. Backup current OpenLDAP configuration and data. 2. Stop the OpenLDAP service. 3. Upgrade to OpenLDAP 2.4.56 or later using your distribution's package manager. 4. Verify the upgrade completed successfully. 5. Restart the OpenLDAP service.
🔧 Temporary Workarounds
Network Access Control
linuxRestrict network access to LDAP servers to only trusted sources using firewall rules.
iptables -A INPUT -p tcp --dport 389 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 389 -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to limit access to LDAP servers only from required clients
- Deploy monitoring and alerting for LDAP service crashes with automated restart capabilities
🔍 How to Verify
Check if Vulnerable:
Check OpenLDAP version: 'slapd -V 2>&1 | grep slapd' or 'ldapsearch -x -H ldap://localhost -b "" -s base "(objectclass=*)" vendorVersion'Check Version:
slapd -V 2>&1 | grep 'slapd'Verify Fix Applied:
Verify version is 2.4.56 or higher using the same commands and ensure LDAP service remains stable during normal operations.📡 Detection & Monitoring
Log Indicators:
- slapd crash logs
- assertion failure messages in syslog
- LDAP service restart events
- abnormal termination of slapd process
Network Indicators:
- Unusual LDAP traffic patterns
- Multiple connection attempts followed by service unavailability
- LDAP protocol anomalies
SIEM Query:
source="syslog" AND (process="slapd" AND (message="assertion fail*" OR message="abnormal termination" OR message="segmentation fault"))🔗 References
- https://bugzilla.redhat.com/show_bug.cgi?id=1899678
- https://git.openldap.org/openldap/openldap/-/commit/ab3915154e69920d480205b4bf5ccb2b391a0a1f#a2feb6ed0257c21c6672793ee2f94eaadc10c72c
- https://lists.apache.org/thread.html/r58af02e294bd07f487e2c64ffc0a29b837db5600e33b6e698b9d696b%40%3Cissues.bookkeeper.apache.org%3E
- https://lists.apache.org/thread.html/rf4c02775860db415b4955778a131c2795223f61cb8c6a450893651e4%40%3Cissues.bookkeeper.apache.org%3E
- https://lists.debian.org/debian-lts-announce/2020/12/msg00008.html
- https://security.netapp.com/advisory/ntap-20210716-0003/
- https://www.debian.org/security/2020/dsa-4792
- https://bugzilla.redhat.com/show_bug.cgi?id=1899678
- https://git.openldap.org/openldap/openldap/-/commit/ab3915154e69920d480205b4bf5ccb2b391a0a1f#a2feb6ed0257c21c6672793ee2f94eaadc10c72c
- https://lists.apache.org/thread.html/r58af02e294bd07f487e2c64ffc0a29b837db5600e33b6e698b9d696b%40%3Cissues.bookkeeper.apache.org%3E
- https://lists.apache.org/thread.html/rf4c02775860db415b4955778a131c2795223f61cb8c6a450893651e4%40%3Cissues.bookkeeper.apache.org%3E
- https://lists.debian.org/debian-lts-announce/2020/12/msg00008.html
- https://security.netapp.com/advisory/ntap-20210716-0003/
- https://www.debian.org/security/2020/dsa-4792
