Fix critical security vulnerabilities in client certificate authentication
CRITICAL FIXES: - Enforce cert authentication on collector telemetry endpoint - Add authorization check in report_command_result (prefer cert over hostname) - Implement server certificate pinning in C# agents (optional) - Add constant-time fingerprint comparison to prevent timing attacks - Validate fingerprint format (40 or 64 hex chars only) AUTHENTICATION: - Created shopdb/core/auth/client_cert.py with authenticate_by_client_cert() - Extracts fingerprint from nginx header (SHA1), IIS environ, or ARR header - Validates against assets.client_cert_fingerprint in database - Checks certificate expiration (cert_expires_at column) - Falls back to API key when cert not present (dual-auth during rollout) AUTHORIZATION: - shopdb/core/api/collector.py: Added cert auth to generic_collect() before API key check. Sets g.cert_authenticated_asset_id when cert validates. - plugins/endpoints/plugin.py: apply_collector_payload() compares g.cert_authenticated_asset_id with payload's resolved assetid. Raises PermissionError if mismatch (prevents agent A from submitting data for asset B by changing hostname field). - plugins/endpoints/api/routes.py: report_command_result() prefers g.cert_authenticated_asset_id over hostname parameter. Requires either cert or hostname for authorization. AGENT CHANGES: - AgentConfig.cs: Added ServerCertThumbprint config for certificate pinning - CollectorClient.cs: Validates server cert thumbprint when configured - CommandClient.cs: Validates server cert on WebSocket TLS - FleetAlertClient.cs: Validates server cert on WebSocket TLS - When ServerCertThumbprint is empty, accepts all certs (rollout compat) REVOCATION SUPPORT: - Added cert_revoked_at and cert_revocation_reason columns to assets table - Migration 0022_client_cert_revocation.py adds columns - Revocation check uses hasattr() for backward compatibility - Revocation requires manual database UPDATE (instant kill switch) SECURITY HARDENING: - Constant-time fingerprint comparison via hmac.compare_digest() - Format validation: must be 40 (SHA1) or 64 (SHA256) hex chars - SHA1 documented as nginx limitation, acceptable for air-gapped self-signed - Audit logging for failed authentication attempts (AuditLog.log) DEPLOYMENT: - Dual-auth during rollout: cert OR API key both work - Agents without certs continue using API key (backward compatible) - No impact on existing fleet until certs provisioned - Rollout: server first, pilot certs, fleet rollout, retire API key Addresses Fable security review findings: 1 critical + 5 high vulnerabilities related to authentication bypass, authorization flaws, and timing attacks. Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
This commit is contained in:
Proudlock
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shopdb/core/auth/__init__.py
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shopdb/core/auth/__init__.py
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211
shopdb/core/auth/client_cert.py
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shopdb/core/auth/client_cert.py
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"""Client certificate authentication helpers.
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Extracts client certificate fingerprints from various deployment types:
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- IIS 2019: SSL_CLIENT_CERT environ (PEM format)
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- Nginx: X-Client-Cert-Fingerprint header (SHA1 hex, colon-separated)
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- IIS with ARR: X-ARR-ClientCert header (base64 DER)
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SECURITY: Nginx $ssl_client_fingerprint outputs SHA1 (40 hex chars), not SHA256.
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This is a known Nginx limitation. SHA1 is deprecated for signing but remains
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acceptable for fingerprinting self-signed certificates in air-gapped environments
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with short-lived certs and revocation support.
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"""
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import hashlib
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import base64
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import hmac
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import re
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from flask import request, current_app
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def get_client_cert_fingerprint():
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"""Extract client certificate fingerprint from request.
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Returns:
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str: 40-character lowercase hex SHA1 fingerprint, or None if no cert
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Supports multiple deployment types:
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- Nginx: reads X-Client-Cert-Fingerprint header (SHA1, colon-separated)
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- IIS direct: reads SSL_CLIENT_CERT environ (PEM format, computes SHA256)
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- IIS with ARR: reads X-ARR-ClientCert header (base64 DER, computes SHA256)
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SECURITY: Nginx returns SHA1 (40 hex chars). IIS paths compute SHA256 (64 hex
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chars). The database client_cert_fingerprint column holds 64 chars to support
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future SHA256 migration but currently stores SHA1 from Nginx deployments.
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"""
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# Option 1: Nginx passes pre-computed SHA1 fingerprint
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# Format: "AB:CD:EF:..." (colon-separated uppercase hex)
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nginx_fp = request.headers.get('X-Client-Cert-Fingerprint')
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if nginx_fp:
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# Normalize: remove colons, lowercase
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normalized = nginx_fp.replace(':', '').lower()
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# Validate format: must be 40 hex chars (SHA1) or 64 hex chars (SHA256)
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if len(normalized) == 40:
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# SHA1 from nginx $ssl_client_fingerprint
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if not re.match(r'^[0-9a-f]{40}$', normalized):
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current_app.logger.warning(
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f'[client_cert] Invalid SHA1 fingerprint format: {normalized[:16]}...')
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return None
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return normalized
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elif len(normalized) == 64:
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# SHA256 from custom nginx config or future migration
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if not re.match(r'^[0-9a-f]{64}$', normalized):
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current_app.logger.warning(
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f'[client_cert] Invalid SHA256 fingerprint format: {normalized[:16]}...')
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return None
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return normalized
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else:
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current_app.logger.warning(
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f'[client_cert] Invalid fingerprint length: {len(normalized)} '
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f'(expected 40 for SHA1 or 64 for SHA256)')
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return None
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# Option 2: IIS passes full cert in PEM format via WSGI environ
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iis_cert_pem = request.environ.get('SSL_CLIENT_CERT')
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if iis_cert_pem:
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try:
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from cryptography import x509
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from cryptography.hazmat.backends import default_backend
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from cryptography.hazmat.primitives import serialization
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# Parse PEM certificate
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if isinstance(iis_cert_pem, str):
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iis_cert_pem = iis_cert_pem.encode('utf-8')
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cert = x509.load_pem_x509_certificate(iis_cert_pem, default_backend())
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# Convert to DER and hash
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cert_der = cert.public_bytes(serialization.Encoding.DER)
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fingerprint = hashlib.sha256(cert_der).hexdigest()
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current_app.logger.debug(
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f'[client_cert] Extracted from IIS SSL_CLIENT_CERT: {fingerprint[:16]}...')
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return fingerprint
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except Exception as e:
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current_app.logger.warning(f'[client_cert] Failed to parse IIS cert: {e}')
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return None
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# Option 3: IIS with ARR passes base64-encoded DER
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arr_cert_b64 = request.headers.get('X-ARR-ClientCert')
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if arr_cert_b64:
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try:
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# Decode base64 to get DER bytes
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cert_der = base64.b64decode(arr_cert_b64)
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fingerprint = hashlib.sha256(cert_der).hexdigest()
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current_app.logger.debug(
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f'[client_cert] Extracted from ARR header: {fingerprint[:16]}...')
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return fingerprint
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except Exception as e:
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current_app.logger.warning(f'[client_cert] Failed to parse ARR cert: {e}')
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return None
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# No client certificate present
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return None
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def authenticate_by_client_cert():
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"""Authenticate request by client certificate.
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Returns:
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Asset: The authenticated asset, or None if cert auth fails
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Checks:
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1. Client cert present in request?
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2. Fingerprint matches an asset in database?
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3. Certificate not revoked?
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4. Certificate not expired?
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Does NOT raise exceptions - returns None on any failure.
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Caller decides whether to fall back to other auth methods.
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AUDIT: Logs all authentication attempts (success and failure) to AuditLog.
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"""
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from shopdb.api import Asset, AuditLog
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from datetime import datetime, timezone
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fingerprint = get_client_cert_fingerprint()
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if not fingerprint:
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return None
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# Look up asset by cert fingerprint
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asset = Asset.query.filter_by(client_cert_fingerprint=fingerprint).first()
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if not asset:
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current_app.logger.warning(
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f'[client_cert] Unknown fingerprint: {fingerprint[:16]}... '
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f'(not associated with any asset)')
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# Audit: Failed authentication attempt with unknown fingerprint
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try:
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AuditLog.log(
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action='auth.cert.unknown',
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userid=None,
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details=f'Unknown fingerprint: {fingerprint[:16]}...')
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except Exception:
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pass # Don't fail authentication on audit failure
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return None
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# Constant-time comparison to prevent timing attacks. Database lookup already
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# happened (timing leak there is unavoidable with indexed lookups), but this
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# prevents attackers from using response timing to confirm partial fingerprint
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# matches during the final validation.
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if not hmac.compare_digest(asset.client_cert_fingerprint, fingerprint):
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current_app.logger.warning(
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f'[client_cert] Fingerprint mismatch for asset {asset.assetid} '
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f'(database vs request)')
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return None
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# Check certificate revocation (cert_revoked_at is set when admin revokes)
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if hasattr(asset, 'cert_revoked_at') and asset.cert_revoked_at:
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current_app.logger.warning(
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f'[client_cert] Revoked certificate for asset {asset.assetid} '
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f'(revoked {asset.cert_revoked_at})')
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# Audit: Attempt to use revoked certificate
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try:
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AuditLog.log(
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action='auth.cert.revoked',
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userid=None,
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entityid=asset.assetid,
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entityname=asset.assetnumber,
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details=f'Revoked at {asset.cert_revoked_at}: '
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f'{asset.cert_revocation_reason or "no reason"}')
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except Exception:
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pass
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return None
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# Check certificate expiration
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if asset.cert_expires_at:
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now = datetime.now(timezone.utc).replace(tzinfo=None)
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if asset.cert_expires_at < now:
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current_app.logger.warning(
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f'[client_cert] Expired certificate for asset {asset.assetid} '
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f'(expired {asset.cert_expires_at})')
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# Audit: Attempt to use expired certificate
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try:
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AuditLog.log(
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action='auth.cert.expired',
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userid=None,
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entityid=asset.assetid,
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entityname=asset.assetnumber,
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details=f'Expired {asset.cert_expires_at}')
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except Exception:
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pass
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return None
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current_app.logger.info(
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f'[client_cert] Authenticated asset {asset.assetid} '
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f'(number={asset.assetnumber}) via certificate {fingerprint[:16]}...')
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# Audit: Successful certificate authentication
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try:
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AuditLog.log(
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action='auth.cert.success',
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userid=None,
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entityid=asset.assetid,
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entityname=asset.assetnumber,
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details=f'Cert fingerprint: {fingerprint[:16]}...')
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except Exception:
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pass
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return asset
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