CVE-2026-44304: Lemur LDAP Filter Injection Enables Post-authentication Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-3r34-vq8m-39gh",
  "modified" : "2026-05-13T16:41:43Z",
  "published" : "2026-05-06T19:16:59Z",
  "aliases" : [ "CVE-2026-44304" ],
  "summary" : "Lemur: LDAP Filter Injection enables post-authentication privilege escalation",
  "details" : "## Description\n\n### Overview\n\nLemur'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.\n\n### Vulnerable Code\n\n**Location:** `lemur/auth/ldap.py`, `_bind()` method\n\n**Filter 1 — User lookup (line ~161):**\n```python\nldap_filter = \"userPrincipalName=%s\" % self.ldap_principal\n```\n\n`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.\n\n**Filter 2 — Active Directory group lookup (line ~189):**\n```python\ngroupfilter = \"(&(objectclass=group)(member:1.2.840.113556.1.4.1941:={}))\".format(userdn)\n```\n\nThe `userdn` value is derived from the LDAP response to the first unsanitized query, making it potentially tainted as well.\n\n### Impact\n\nAn authenticated LDAP user can:\n\n1. Inject LDAP filter syntax into the username field during login\n2. Manipulate the group membership query to return arbitrary groups\n3. Be assigned the `admin` role or any other privileged role in Lemur\n4. Gain unauthorized access to all certificates, private keys (via `/certificates/<id>/key`), and CA configurations\n5. Issue certificates under any authority\n\n### Exploitation Constraint\n\nThe `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**.\n\n### Steps to Reproduce\n\n1. Deploy Lemur with LDAP authentication enabled:\n   ```python\n   LDAP_AUTH = True\n   LDAP_IS_ACTIVE_DIRECTORY = True\n   LDAP_BIND_URI = \"ldaps://dc.corp.example.com\"\n   LDAP_BASE_DN = \"DC=corp,DC=example,DC=com\"\n   LDAP_EMAIL_DOMAIN = \"corp.example.com\"\n   ```\n2. Create a valid LDAP user account\n3. Send login request with crafted username containing LDAP metacharacters:\n   ```\n   POST /auth/login\n   Content-Type: application/json\n\n   {\n     \"username\": \"validuser)(memberOf=CN=LemurAdmins,DC=corp,DC=example,DC=com\",\n     \"password\": \"validpassword\"\n   }\n   ```\n4. The LDAP filter becomes:\n   ```\n   userPrincipalName=validuser)(memberOf=CN=LemurAdmins,DC=corp,DC=example,DC=com@corp.example.com\n   ```\n5. Depending on the LDAP server's parsing, this can alter query semantics\n6. The user is assigned roles they should not have access to\n\n### Remediation\n\nApply `ldap.filter.escape_filter_chars()` to all user-controlled values before interpolation:\n\n```python\nfrom ldap.filter import escape_filter_chars\n\n# Fix 1: User lookup filter\nldap_filter = \"userPrincipalName=%s\" % escape_filter_chars(self.ldap_principal)\n\n# Fix 2: Active Directory group filter\ngroupfilter = \"(&(objectclass=group)(member:1.2.840.113556.1.4.1941:={}))\".format(\n    escape_filter_chars(userdn)\n)\n```\n\n### Resources\n\n- CWE-90: https://cwe.mitre.org/data/definitions/90.html\n- OWASP LDAP Injection: https://owasp.org/www-community/attacks/LDAP_Injection\n- Python ldap.filter.escape_filter_chars: https://www.python-ldap.org/en/python-ldap-3.4.0/reference/ldap-filter.html",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "lemur"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.9.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/Netflix/lemur/security/advisories/GHSA-3r34-vq8m-39gh"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-44304"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/Netflix/lemur"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/Netflix/lemur/releases/tag/v1.9.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-90" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-06T19:16:59Z",
    "nvd_published_at" : "2026-05-12T22:16:37Z"
  }
}