Summary
Lemur: LDAP Authentication Globally Disables TLS Certificate Verification When LDAPUSETLS Is Enabled
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
if self.ldap_use_tls:
ldap.set_option(ldap.OPT_X_TLS_REQUIRE_CERT, ldap.OPT_X_TLS_NEVER)
Key issues:
ldap.set_option()is a global call (as opposed toself.ldap_client.set_option()), meaning it disables TLS verification for the entire Python process, not just this connectionOPT_X_TLS_NEVERmeans no certificate validation is performed whatsoever, self-signed, expired, wrong hostname, and revoked certificates are all silently accepted- There is no configuration option to override this behavior, TLS verification is always disabled when TLS is enabled
Steps to Reproduce
Deploy Lemur with LDAP TLS enabled:
LDAP_AUTH = True LDAP_USE_TLS = True LDAP_BIND_URI = "ldaps://dc.corp.example.com"Intercept the LDAP connection using a TLS proxy (e.g.,
mitmproxyorstunnel):# 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.pemPoint Lemur's
LDAP_BIND_URIat the proxy (or perform ARP spoofing/DNS hijacking)Observe that Lemur connects without any certificate verification error
All credentials are visible in the proxy's TLS session
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
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.
CVE-2026-44305 has a CVSS score of 6.8 (Medium). The vector is reachable from an adjacent network, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.9.0); upgrading removes the vulnerable code path.
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.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Remove the global TLS verification bypass and default to strict verification:
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:
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)
Frequently Asked Questions
- What is CVE-2026-44305? CVE-2026-44305 is a medium-severity security vulnerability in lemur (pip), affecting versions < 1.9.0. It is fixed in 1.9.0.
- How severe is CVE-2026-44305? CVE-2026-44305 has a CVSS score of 6.8 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of lemur are affected by CVE-2026-44305? lemur (pip) versions < 1.9.0 is affected.
- Is there a fix for CVE-2026-44305? Yes. CVE-2026-44305 is fixed in 1.9.0. Upgrade to this version or later.
- Is CVE-2026-44305 exploitable, and should I be worried? Whether CVE-2026-44305 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-2026-44305 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-2026-44305? Upgrade
lemurto 1.9.0 or later.