CVE-2026-44304 — lemur
HIGHCVE-2026-44304 is a high-severity (CVSS 8.1) CWE-90 vulnerability in lemur. A fix is available for lemur — see the affected versions and patch details below.
Lemur: LDAP Filter Injection enables post-authentication privilege escalation
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-44304.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-44304 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
lemurReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
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):
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):
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:
- Inject LDAP filter syntax into the username field during login
- Manipulate the group membership query to return arbitrary groups
- Be assigned the
adminrole or any other privileged role in Lemur - Gain unauthorized access to all certificates, private keys (via
/certificates/<id>/key), and CA configurations - 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
- Deploy Lemur with LDAP authentication enabled:
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" - Create a valid LDAP user account
- 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" } - The LDAP filter becomes:
userPrincipalName=validuser)(memberOf=CN=LemurAdmins,DC=corp,DC=example,[email protected] - Depending on the LDAP server's parsing, this can alter query semantics
- 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:
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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | lemur | all versions | 1.9.0pip install --upgrade 'lemur==1.9.0' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for lemur, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update lemur to 1.9.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44304 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-44304 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-44304. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-44304 in your dependencies?
O3 Security finds CVE-2026-44304 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.