CVE-2020-15719 Overview
CVE-2020-15719 is a certificate validation vulnerability affecting libldap in certain third-party OpenLDAP packages. The flaw occurs when these packages assert RFC6125 support but improperly validate certificates by considering the Common Name (CN) field even when there is a non-matching subjectAltName (SAN). This behavior violates RFC6125 certificate verification standards and can enable man-in-the-middle attacks against LDAP connections.
Critical Impact
Attackers positioned in a network path can potentially intercept and manipulate LDAP communications by presenting certificates with matching CN values but non-matching SAN entries, bypassing intended certificate validation controls.
Affected Products
- OpenLDAP (various versions in third-party packages)
- Red Hat Enterprise Linux 8.0
- openSUSE Leap 15.1 and 15.2
- McAfee Policy Auditor
- Oracle Blockchain Platform
Discovery Timeline
- 2020-07-14 - CVE CVE-2020-15719 published to NVD
- 2024-11-21 - Last updated in NVD database
Technical Details for CVE-2020-15719
Vulnerability Analysis
This vulnerability stems from improper implementation of RFC6125 certificate validation in libldap. RFC6125 specifies how applications should verify the identity of a server based on the information presented in X.509 certificates. According to the standard, when a certificate contains a subjectAltName (SAN) extension, the Common Name (CN) in the subject field should be ignored for verification purposes.
The affected third-party OpenLDAP packages incorrectly fall back to checking the CN field even when a SAN extension exists but does not match the expected hostname. This creates a security gap where an attacker with a certificate containing a matching CN but mismatched SAN could successfully authenticate to a client that should reject the connection.
Root Cause
The root cause is classified as CWE-295: Improper Certificate Validation. The vulnerability exists because the certificate validation logic in affected libldap implementations does not properly enforce RFC6125 requirements. Specifically, the code considers CN validation as a fallback even when SAN entries are present, rather than exclusively using SAN when available as mandated by RFC6125.
Attack Vector
The attack requires a network-based position where the attacker can intercept LDAP connections (man-in-the-middle). The attacker must also possess a valid certificate from a trusted Certificate Authority where:
- The subjectAltName (SAN) does not match the target server's hostname
- The Common Name (CN) matches the target server's hostname
When a vulnerable LDAP client connects to the attacker-controlled endpoint, the improper validation logic will accept the certificate despite the SAN mismatch, allowing the attacker to intercept or manipulate the LDAP communication. User interaction is required as the victim must initiate an LDAP connection that traverses the attacker's network position.
The vulnerability mechanism involves the certificate validation process checking CN as a fallback when SAN validation fails, contrary to RFC6125 specifications. For detailed technical analysis, refer to the OpenLDAP Bug Report #9266.
Detection Methods for CVE-2020-15719
Indicators of Compromise
- LDAP connection logs showing certificate validation warnings or anomalies
- Network traffic analysis revealing unexpected certificate presentations during LDAP TLS handshakes
- Certificate monitoring alerts for LDAP services showing SAN/CN mismatches in accepted certificates
Detection Strategies
- Monitor LDAP service logs for certificate validation events and warnings
- Deploy network intrusion detection rules to identify potential man-in-the-middle positioning on LDAP ports (389, 636)
- Implement certificate transparency monitoring for domains used in LDAP infrastructure
- Audit OpenLDAP package versions across the environment to identify vulnerable installations
Monitoring Recommendations
- Enable verbose TLS logging on LDAP clients and servers to capture certificate validation details
- Configure SIEM alerts for unusual LDAP connection patterns or certificate-related events
- Implement network flow analysis to detect potential interception points in LDAP traffic paths
- Regularly audit certificate configurations and validation settings across LDAP infrastructure
How to Mitigate CVE-2020-15719
Immediate Actions Required
- Identify all systems running affected OpenLDAP packages (particularly third-party distributions)
- Prioritize patching systems that handle sensitive LDAP authentication traffic
- Review network segmentation to minimize exposure of LDAP services to untrusted network paths
- Consider implementing additional certificate pinning where feasible
Patch Information
The vulnerability has been addressed in updated packages from affected vendors. Red Hat has released the fix in openldap-2.4.46-10.el8 for Red Hat Enterprise Linux 8. Administrators should apply the appropriate patches:
- Red Hat Enterprise Linux: Apply RHBA-2019:3674 or later errata
- openSUSE Leap: Apply updates referenced in the openSUSE Security Announcements
- McAfee Policy Auditor: Review McAfee Security Bulletin SB10365
- Oracle Blockchain Platform: Apply patches from Oracle Security Alert CPUAPR2022
Workarounds
- Implement network-level controls to prevent man-in-the-middle positioning on LDAP communication paths
- Use VPN or other encrypted tunnels for LDAP traffic traversing untrusted networks
- Deploy mutual TLS authentication where both client and server certificates are validated
- Consider alternative LDAP client libraries with proper RFC6125 compliance until patching is complete
# Verify OpenLDAP package version on RHEL/CentOS 8
rpm -qa | grep openldap
# Check if the patched version is installed (should be >= 2.4.46-10.el8)
rpm -q openldap --queryformat '%{VERSION}-%{RELEASE}\n'
# Update to patched version on RHEL/CentOS 8
sudo yum update openldap
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
