CVE-2020-25709
📋 TL;DR
CVE-2020-25709 is an assertion failure vulnerability in OpenLDAP's slapd server that allows remote attackers to crash the service by sending specially crafted packets. This affects all systems running vulnerable versions of OpenLDAP with slapd exposed. The primary impact is denial of service through service crashes.
💻 Affected Systems
- OpenLDAP
📦 What is this software?
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⚠️ Risk & Real-World Impact
Worst Case
Complete service outage of OpenLDAP directory services, potentially disrupting authentication, authorization, and directory-dependent applications across the organization.
Likely Case
Intermittent slapd crashes causing service disruptions, failed authentication attempts, and degraded directory service performance.
If Mitigated
Minimal impact if slapd is not exposed to untrusted networks and proper network segmentation is in place.
🎯 Exploit Status
The vulnerability is triggered by sending malformed packets to slapd, making exploitation straightforward. Public exploit details are available in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: OpenLDAP 2.4.58 or later
Vendor Advisory: https://www.openldap.org/software/release/changes.html
Restart Required: Yes
Instructions:
1. Download OpenLDAP 2.4.58+ from openldap.org. 2. Stop slapd service. 3. Install updated version. 4. Restart slapd service. 5. Verify service is running and responding.
🔧 Temporary Workarounds
Network Access Control
linuxRestrict network access to slapd ports (default 389/636) to trusted sources only using firewall rules.
iptables -A INPUT -p tcp --dport 389 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 389 -j DROP
Rate Limiting
linuxImplement connection rate limiting to reduce impact of DoS attempts.
iptables -A INPUT -p tcp --dport 389 -m state --state NEW -m limit --limit 10/min --limit-burst 20 -j ACCEPT
🧯 If You Can't Patch
- Implement strict network segmentation to isolate OpenLDAP servers from untrusted networks.
- Deploy intrusion prevention systems (IPS) with rules to detect and block malformed LDAP packets.
🔍 How to Verify
Check if Vulnerable:
Check OpenLDAP version: slapd -VV 2>&1 | grep -i 'openldap' and compare to affected versions (2.4.0-2.4.57).Check Version:
slapd -VV 2>&1 | grep -i 'openldap'Verify Fix Applied:
Verify version is 2.4.58 or later with slapd -VV and test service functionality with ldapsearch -x -b '' -s base.📡 Detection & Monitoring
Log Indicators:
- slapd crash logs
- assertion failure messages in syslog
- unexpected slapd restarts
Network Indicators:
- Unusual volume of malformed LDAP packets to port 389/636
- LDAP protocol violations
SIEM Query:
source="syslog" AND ("slapd" AND ("assertion" OR "crash" OR "segfault"))🔗 References
- http://seclists.org/fulldisclosure/2021/Feb/14
- https://bugzilla.redhat.com/show_bug.cgi?id=1899675
- 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://support.apple.com/kb/HT212147
- https://www.debian.org/security/2020/dsa-4792
- http://seclists.org/fulldisclosure/2021/Feb/14
- https://bugzilla.redhat.com/show_bug.cgi?id=1899675
- 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://support.apple.com/kb/HT212147
- https://www.debian.org/security/2020/dsa-4792
