PT-2026-59240 · Pypi · Lemur

Published

2026-07-13

·

Updated

2026-07-13

CVSS v3.1

8.1

High

VectorAV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

Description

Overview

Lemur's LDAP authentication module (lemur/auth/ldap.py) constructs LDAP search filters using unsanitized user input via Python string interpolation. An authenticated LDAP user can inject LDAP filter metacharacters through the username field to manipulate group membership queries and escalate their privileges to administrator.

Vulnerable Code

Location: lemur/auth/ldap.py, bind() method
Filter 1 — User lookup (line ~161):
python
ldap filter = "userPrincipalName=%s" % self.ldap principal
self.ldap principal is derived directly from args["username"] submitted at POST /auth/login with no sanitization. The ldap.filter.escape filter chars() function is never called.
Filter 2 — Active Directory group lookup (line ~189):
python
groupfilter = "(&(objectclass=group)(member:1.2.840.113556.1.4.1941:={}))".format(userdn)
The userdn value is derived from the LDAP response to the first unsanitized query, making it potentially tainted as well.

Impact

An authenticated LDAP user can:
  1. Inject LDAP filter syntax into the username field during login
  2. Manipulate the group membership query to return arbitrary groups
  3. Be assigned the admin role or any other privileged role in Lemur
  4. Gain unauthorized access to all certificates, private keys (via /certificates/<id>/key), and CA configurations
  5. Issue certificates under any authority

Exploitation Constraint

The simple bind s() call must succeed before the injectable filter is reached, so the attacker requires valid LDAP credentials. This is a post-authentication privilege escalation.

Steps to Reproduce

  1. Deploy Lemur with LDAP authentication enabled:
python
LDAP AUTH = True
LDAP IS ACTIVE DIRECTORY = True
LDAP BIND URI = "ldaps://dc.corp.example.com"
LDAP BASE DN = "DC=corp,DC=example,DC=com"
LDAP EMAIL DOMAIN = "corp.example.com"
  1. Create a valid LDAP user account
  2. Send login request with crafted username containing LDAP metacharacters:
POST /auth/login
Content-Type: application/json

{
 "username": "validuser)(memberOf=CN=LemurAdmins,DC=corp,DC=example,DC=com",
 "password": "validpassword"
}
  1. The LDAP filter becomes:
userPrincipalName=validuser)(memberOf=CN=LemurAdmins,DC=corp,DC=example,DC=com@corp.example.com
  1. Depending on the LDAP server's parsing, this can alter query semantics
  2. The user is assigned roles they should not have access to

Remediation

Apply ldap.filter.escape filter chars() to all user-controlled values before interpolation:
python
from ldap.filter import escape filter chars

# Fix 1: User lookup filter
ldap filter = "userPrincipalName=%s" % escape filter chars(self.ldap principal)

# Fix 2: Active Directory group filter
groupfilter = "(&(objectclass=group)(member:1.2.840.113556.1.4.1941:={}))".format(
  escape filter chars(userdn)
)

Resources

Fix

Found an issue in the description? Have something to add? Feel free to write us 👾
dbugs@ptsecurity.com

Related Identifiers

PYSEC-2026-2585

Affected Products

Lemur