GHSA-3r34-vq8m-39gh Lemur: LDAP Filter Injection enables post-authentication privilege escalation

• PyPI lemur: < 1.9.0 → fixed in 1.9.0

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//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" ``` 2. Create a valid LDAP user account 3. 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" } ``` 4. The LDAP filter becomes: ``` userPrincipalName=validuser)(memberOf=CN=LemurAdmins,DC=corp,DC=example,[email protected] ``` 5. Depending on the LDAP server's parsing, this can alter query semantics 6. 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 • CWE-90: https://cwe.mitre.org/data/definitions/90.html • OWASP LDAP Injection: https://owasp.org/www-community/attacks/LDAP_Injection • Python ldap.filter.escape_filter_chars: https://www.python-ldap.org/en/python-ldap-3.4.0/reference/ldap-filter.html