CVE-2026-44305

MEDIUM6.8EPSS 0.01%

Lemur: LDAP Authentication Globally Disables TLS Certificate Verification When LDAP_USE_TLS Is Enabled

Published: 5/6/2026Modified: 5/13/2026

Description

## Description ### Overview When LDAP TLS is enabled (`LDAP_USE_TLS = True`), Lemur's LDAP authentication module unconditionally disables TLS certificate verification at the **global** `ldap` module level. This allows a man-in-the-middle attacker positioned between Lemur and the LDAP server to intercept all authentication credentials. ### Vulnerable Code **Location:** `lemur/auth/ldap.py`, `_bind()` method, line ~172 ```python if self.ldap_use_tls: ldap.set_option(ldap.OPT_X_TLS_REQUIRE_CERT, ldap.OPT_X_TLS_NEVER) ``` Key issues: 1. `ldap.set_option()` is a **global** call (as opposed to `self.ldap_client.set_option()`), meaning it disables TLS verification for the entire Python process, not just this connection 2. `OPT_X_TLS_NEVER` means no certificate validation is performed whatsoever — self-signed, expired, wrong hostname, and revoked certificates are all silently accepted 3. There is no configuration option to override this behavior — TLS verification is always disabled when TLS is enabled ### Impact A network-positioned attacker (man-in-the-middle) between Lemur and the LDAP server can: - **Intercept all LDAP credentials** (usernames and plaintext passwords) for every user who authenticates - **Modify LDAP responses** to inject arbitrary group memberships, granting admin access - **Compromise the entire PKI infrastructure** managed by Lemur, since authentication controls access to certificates and private keys This is particularly severe because Lemur is a certificate management system — the tool designed to manage TLS security is itself vulnerable to a TLS attack. ### Steps to Reproduce 1. Deploy Lemur with LDAP TLS enabled: ```python LDAP_AUTH = True LDAP_USE_TLS = True LDAP_BIND_URI = "ldaps://dc.corp.example.com" ``` 2. Intercept the LDAP connection using a TLS proxy (e.g., `mitmproxy` or `stunnel`): ```bash # Generate a self-signed certificate openssl req -x509 -newkey rsa:2048 -keyout mitm.key -out mitm.crt -days 1 -nodes -subj "/CN=mitm" # Proxy LDAP traffic stunnel -d 0.0.0.0:636 -r real-ldap-server:636 -p mitm.pem ``` 3. Point Lemur's `LDAP_BIND_URI` at the proxy (or perform ARP spoofing/DNS hijacking) 4. Observe that Lemur connects without any certificate verification error 5. All credentials are visible in the proxy's TLS session ### Remediation Remove the global TLS verification bypass and default to strict verification: ```python if self.ldap_use_tls: # Use instance-level option, not global self.ldap_client.set_option(ldap.OPT_X_TLS_REQUIRE_CERT, ldap.OPT_X_TLS_DEMAND) self.ldap_client.set_option(ldap.OPT_PROTOCOL_VERSION, 3) if self.ldap_cacert_file: self.ldap_client.set_option(ldap.OPT_X_TLS_CACERTFILE, self.ldap_cacert_file) ``` If backward compatibility is needed, make it configurable with a secure default: ```python tls_require_cert = current_app.config.get("LDAP_TLS_REQUIRE_CERT", ldap.OPT_X_TLS_DEMAND) self.ldap_client.set_option(ldap.OPT_X_TLS_REQUIRE_CERT, tls_require_cert) ``` ### Resources - CWE-295: https://cwe.mitre.org/data/definitions/295.html - python-ldap TLS documentation: https://www.python-ldap.org/en/python-ldap-3.4.0/reference/ldap.html#tls-options

Affected packages (1)

CVSS scores

SourceVersionSeverityVector
osvCVSS 3.1MEDIUM6.8CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

References (5)