CVE-2011-1024 in OpenLDAP
Summary
by MITRE
chain.c in back-ldap in OpenLDAP 2.4.x before 2.4.24, when a master-slave configuration with a chain overlay and ppolicy_forward_updates (aka authentication-failure forwarding) is used, allows remote authenticated users to bypass external-program authentication by sending an invalid password to a slave server.
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Analysis
by VulDB Data Team • 10/19/2021
The vulnerability identified as CVE-2011-1024 affects OpenLDAP versions prior to 2.4.24 and specifically targets the chain.c component within the back-ldap backend. This flaw exists in master-slave replication configurations that utilize the chain overlay functionality combined with ppolicy_forward_updates parameter, creating a security weakness that can be exploited by authenticated remote attackers to circumvent external authentication mechanisms. The vulnerability stems from improper handling of authentication failure forwarding within the LDAP replication framework, where the system fails to properly validate authentication responses from slave servers.
The technical implementation of this vulnerability occurs through the authentication-failure forwarding mechanism that is designed to redirect authentication attempts from slave servers back to the master server for validation. When ppolicy_forward_updates is enabled, the system should forward authentication failures to maintain consistency across the replication topology. However, the flaw allows attackers to send invalid passwords to slave servers while the master server continues to accept valid credentials, creating a scenario where authentication bypass becomes possible. This occurs because the chain overlay does not properly verify that authentication responses from slave servers are legitimate and originate from the intended authentication process.
The operational impact of this vulnerability is significant within environments that rely on LDAP replication for authentication services, particularly in enterprise networks where master-slave configurations are common. Attackers can exploit this weakness to gain unauthorized access to systems that depend on the LDAP authentication framework, potentially compromising user accounts and sensitive data. The vulnerability affects the integrity of the authentication process by allowing attackers to manipulate the authentication flow, effectively bypassing the security controls that should prevent unauthorized access. This type of vulnerability can lead to privilege escalation, data breaches, and unauthorized system access within the affected network infrastructure.
Organizations using OpenLDAP versions 2.4.x before 2.4.24 with master-slave configurations and chain overlays should immediately implement the available patch from OpenLDAP version 2.4.24 or later. The mitigation strategy should include disabling ppolicy_forward_updates if not strictly required, implementing additional authentication monitoring, and reviewing replication configurations for proper authentication validation. This vulnerability aligns with CWE-284 Access Control Issues and follows patterns similar to those described in ATT&CK technique T1078 Valid Accounts, where attackers leverage legitimate authentication mechanisms to bypass security controls. Network segmentation and monitoring of LDAP authentication traffic should also be implemented to detect potential exploitation attempts and prevent unauthorized access to critical systems.