Keylime Missing Authentication for Critical Function and Improper Authentication

Impact

The Keylime registrar does not enforce mutual TLS (mTLS) client certificate authentication since version 7.12.0. The registrar's TLS context is configured with ssl.CERT_OPTIONAL instead of ssl.CERT_REQUIRED, allowing any client to connect to protected API endpoints without presenting a valid client certificate.

Who is impacted:

• All Keylime deployments running versions 7.12.0 through 7.13.0
• Environments where the registrar HTTPS port (default 8891) is network-accessible to untrusted clients

What an attacker can do:

• List all registered agents (GET /v2/agents/) - enumerate the entire agent inventory
• Retrieve agent details (GET /v2/agents/{uuid}) - obtain public TPM keys, certificates, and network locations (IP/port) of any agent
• Delete any agent (DELETE /v2/agents/{uuid}) - remove agents from the registry, disrupting attestation services

Note: The exposed TPM data (EK, AK, certificates) consists of public keys and certificates. Private keys remain protected within TPM hardware. The HMAC secret used for challenge-response validation is stored in the database but is not exposed via the API.

Affected versions: >= 7.12.0, <= 7.13.0

Fixed versions: 7.12.2, >= 7.13.1

Patches

A patch for the affected released versions is available. It removes the line that override the configuration of ssl.verify_mode, leaving the CERT_REQUIRED value set by web_util.init_mtls():

diff --git a/keylime/web/base/server.py b/keylime/web/base/server.py
index 1d9a9c2..859b23a 100644
--- a/keylime/web/base/server.py
+++ b/keylime/web/base/server.py
@@ -2,7 +2,6 @@ import asyncio
 import multiprocessing
 from abc import ABC, abstractmethod
 from functools import wraps
-from ssl import CERT_OPTIONAL
 from typing import TYPE_CHECKING, Any, Callable, Optional

 import tornado
@@ -252,7 +251,6 @@ class Server(ABC):
         self._https_port = config.getint(component, "tls_port", fallback=0)
         self._max_upload_size = config.getint(component, "max_upload_size", fallback=104857600)
         self._ssl_ctx = web_util.init_mtls(component)
-        self._ssl_ctx.verify_mode = CERT_OPTIONAL

     def _get(self, pattern: str, controller: type["Controller"], action: str, allow_insecure: bool = False) -> None:
         """Creates a new route to handle incoming GET requests issued for paths which match the given

Users should upgrade to the patched version once it is released.

Workarounds

If upgrading is not immediately possible, apply one of the following mitigations:

1. Network isolation (Recommended)

Restrict access to the registrar HTTPS port (default 8891) using firewall rules to allow only trusted hosts (verifier, tenant):

Example using iptables

iptables -A INPUT -p tcp --dport 8891 -s <verifier_ip> -j ACCEPT
iptables -A INPUT -p tcp --dport 8891 -s <tenant_ip> -j ACCEPT
iptables -A INPUT -p tcp --dport 8891 -j DROP

2. Reverse proxy with mTLS enforcement

Deploy a reverse proxy (nginx, HAProxy) in front of the registrar that enforces client certificate authentication:

Example nginx configuration

server {
    listen 8891 ssl;
    ssl_certificate /path/to/server.crt;
    ssl_certificate_key /path/to/server.key;
    ssl_client_certificate /path/to/ca.crt;
    ssl_verify_client on;  # Enforce client certificates

    location / {
        proxy_pass https://localhost:8892;  # Internal registrar port
    }
}