CVE-2023-25613: Apache Kerby LDAP Injection Vulnerability

CVE-2023-25613 Overview

An LDAP Injection vulnerability exists in the LdapIdentityBackend of Apache Kerby before version 2.0.3. This vulnerability allows attackers to manipulate LDAP queries through specially crafted input, potentially leading to unauthorized access to sensitive directory information, authentication bypass, or modification of directory data.

Critical Impact

This LDAP Injection vulnerability in Apache Kerby's identity backend could allow unauthenticated remote attackers to manipulate LDAP queries, potentially compromising the entire authentication infrastructure and exposing sensitive directory data.

Affected Products

• Apache Kerby LDAP Backend (versions prior to 2.0.3)
• Applications utilizing Apache Kerby's LdapIdentityBackend component
• Kerberos implementations leveraging Apache Kerby for LDAP-based identity management

Discovery Timeline

• 2023-02-20 - CVE-2023-25613 published to NVD
• 2025-08-11 - Last updated in NVD database

Technical Details for CVE-2023-25613

Vulnerability Analysis

This vulnerability falls under CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component - Injection). The LdapIdentityBackend component in Apache Kerby fails to properly sanitize user-supplied input before incorporating it into LDAP queries. This lack of input validation allows attackers to inject malicious LDAP filter components or modify query structure, enabling unauthorized data retrieval or manipulation of directory operations.

Apache Kerby is a Java implementation of Kerberos, which is widely used for authentication in enterprise environments. The LDAP backend provides identity services by querying LDAP directories. When user input is not properly escaped before being used in LDAP filter construction, attackers can exploit this to alter the intended query logic.

Root Cause

The root cause of this vulnerability is improper input validation and lack of proper escaping of special LDAP characters in user-supplied data within the LdapIdentityBackend component. When constructing LDAP search filters, the application does not neutralize metacharacters such as *, (, ), \, and null bytes that have special meaning in LDAP filter syntax. This allows attackers to break out of the intended filter context and inject arbitrary LDAP filter expressions.

Attack Vector

The vulnerability is exploitable over the network without requiring authentication or user interaction. An attacker can craft malicious input containing LDAP metacharacters that, when processed by the vulnerable LdapIdentityBackend, modifies the structure of the resulting LDAP query.

Common attack techniques include:

• Filter manipulation: Injecting )( sequences to close existing filters and introduce new conditions
• Wildcard abuse: Using * characters to match arbitrary values
• OR condition injection: Adding | operators to bypass authentication checks
• Attribute enumeration: Extracting directory schema information through error-based techniques

For example, if user input is directly concatenated into an LDAP filter like (uid={input}), an attacker could supply *)(objectClass=* to transform the query into one that returns all objects in the directory. For detailed technical information, refer to the Apache Security Mailing List Discussion.

Detection Methods for CVE-2023-25613

Indicators of Compromise

• Anomalous LDAP queries containing unusual filter syntax or metacharacters such as *, )(, |, or encoded null bytes
• Unexpected authentication successes or failures in Kerberos/LDAP logs
• High volume of LDAP search operations from a single source
• Directory access logs showing queries for sensitive attributes or bulk data retrieval

Detection Strategies

• Monitor LDAP server logs for queries containing injection patterns such as )(, |(, or excessive wildcard characters
• Implement application-layer logging to capture raw input to the LdapIdentityBackend before query construction
• Deploy network-based intrusion detection signatures for LDAP injection attempts
• Review Apache Kerby application logs for authentication anomalies or unexpected directory operations

Monitoring Recommendations

• Enable detailed audit logging on LDAP directory servers to capture all search and bind operations
• Configure alerting for LDAP queries returning unusually large result sets
• Monitor network traffic on LDAP ports (389, 636) for suspicious patterns
• Implement baseline analysis of normal LDAP query patterns to detect deviations

How to Mitigate CVE-2023-25613

Immediate Actions Required

• Upgrade Apache Kerby to version 2.0.3 or later immediately
• Review and audit all applications using the LdapIdentityBackend component
• Implement network segmentation to limit direct access to LDAP infrastructure
• Enable enhanced logging on both Apache Kerby and LDAP directory servers

Patch Information

Apache has addressed this vulnerability in Apache Kerby version 2.0.3. Organizations should upgrade to this version or later to remediate the LDAP Injection vulnerability. Review the Apache Security Mailing List Discussion for additional details regarding the fix and upgrade guidance.

Workarounds

• Implement input validation at the application layer to filter LDAP metacharacters before they reach the LdapIdentityBackend
• Deploy a Web Application Firewall (WAF) or similar security control to inspect and block requests containing LDAP injection patterns
• Restrict LDAP directory permissions to limit the impact of successful injection attacks
• Consider using parameterized LDAP queries or LDAP escaping functions as a defense-in-depth measure until patching is complete

# Configuration example - Input validation for LDAP special characters
# Ensure these characters are escaped or rejected: * ( ) \ / NUL
# Example validation regex pattern (apply at application input boundary)
# Pattern to detect potential LDAP injection: .*[*()\\\\x00].*

# For Apache Kerby upgrade (Maven dependency update)
# Update pom.xml to use patched version:
# <dependency>
#   <groupId>org.apache.kerby</groupId>
#   <artifactId>kerby-ldap-backend</artifactId>
#   <version>2.0.3</version>
# </dependency>