Kerberos Constrained Delegation
Qu'est-ce que Kerberos Constrained Delegation ?
Kerberos Constrained DelegationAn Active Directory delegation mode that allows a service to impersonate users only to a specified set of target services — safer than unconstrained delegation, but still abused via S4U2Self / S4U2Proxy attacks when misconfigured.
Kerberos Constrained Delegation (KCD), introduced with Windows Server 2003, restricts which other services an account can impersonate a user to: the account's `msDS-AllowedToDelegateTo` attribute lists exactly those target SPNs. KCD comes in two flavors. Classic KCD requires Domain Admin to configure the trust on the delegating account. Resource-Based Constrained Delegation (RBCD), introduced in Windows Server 2012, inverts the configuration so the target service controls who can impersonate to it via `msDS-AllowedToActOnBehalfOfOtherIdentity` — useful for cross-forest scenarios. KCD is far safer than unconstrained delegation, but it is not safe by default: attackers with control of an account that has constrained delegation rights can use S4U2Self to mint tickets for arbitrary users (including Domain Admins) and then S4U2Proxy to access the allowed targets, an attack chain documented since the 2018 Elad Shamir 'Wagging the Dog' research. RBCD attacks via control of computer-account writes (CVE-2021-42278/42287, sAMAccountName spoofing) are equally well known. Modern hardening includes Protected Users group membership for sensitive accounts, the 'Account is sensitive and cannot be delegated' flag, and rigorous review of all delegation attributes in AD.
● Exemples
- 01
A web application's service account is constrained to delegate only to the SQL Server SPN; the same account cannot impersonate users to other services.
- 02
A red-team that gains write access to a computer object configures it for RBCD and S4U2Selfs into Domain Admin, demonstrating the need to restrict ms-DS-MachineAccountQuota.
● Questions fréquentes
Qu'est-ce que Kerberos Constrained Delegation ?
An Active Directory delegation mode that allows a service to impersonate users only to a specified set of target services — safer than unconstrained delegation, but still abused via S4U2Self / S4U2Proxy attacks when misconfigured. Cette notion relève de la catégorie Identité et accès en cybersécurité.
Que signifie Kerberos Constrained Delegation ?
An Active Directory delegation mode that allows a service to impersonate users only to a specified set of target services — safer than unconstrained delegation, but still abused via S4U2Self / S4U2Proxy attacks when misconfigured.
Comment fonctionne Kerberos Constrained Delegation ?
Kerberos Constrained Delegation (KCD), introduced with Windows Server 2003, restricts which other services an account can impersonate a user to: the account's `msDS-AllowedToDelegateTo` attribute lists exactly those target SPNs. KCD comes in two flavors. Classic KCD requires Domain Admin to configure the trust on the delegating account. Resource-Based Constrained Delegation (RBCD), introduced in Windows Server 2012, inverts the configuration so the target service controls who can impersonate to it via `msDS-AllowedToActOnBehalfOfOtherIdentity` — useful for cross-forest scenarios. KCD is far safer than unconstrained delegation, but it is not safe by default: attackers with control of an account that has constrained delegation rights can use S4U2Self to mint tickets for arbitrary users (including Domain Admins) and then S4U2Proxy to access the allowed targets, an attack chain documented since the 2018 Elad Shamir 'Wagging the Dog' research. RBCD attacks via control of computer-account writes (CVE-2021-42278/42287, sAMAccountName spoofing) are equally well known. Modern hardening includes Protected Users group membership for sensitive accounts, the 'Account is sensitive and cannot be delegated' flag, and rigorous review of all delegation attributes in AD.
Comment se défendre contre Kerberos Constrained Delegation ?
Les défenses contre Kerberos Constrained Delegation combinent habituellement des contrôles techniques et des pratiques opérationnelles, comme détaillé dans la définition ci-dessus.
Quels sont les autres noms de Kerberos Constrained Delegation ?
Noms alternatifs courants : KCD, Resource-Based Constrained Delegation, RBCD.
● Termes liés
- identity-access№ 652
Kerberos
Protocole d'authentification réseau à base de tickets utilisant la cryptographie symétrique et un Centre de Distribution de Clés de confiance pour offrir une authentification unique sécurisée.
- identity-access№ 014
Active Directory
Service d'annuaire d'entreprise de Microsoft pour les réseaux Windows, qui assure l'authentification, l'autorisation et la gestion centralisée des stratégies pour utilisateurs, machines et ressources.
- identity-access№ 654
Kerberos Unconstrained Delegation
An Active Directory configuration that lets a service receive and store TGTs for any authenticating user, allowing it to impersonate them to any other service — a high-impact misconfiguration repeatedly abused for credential theft and domain compromise.
- attacks№ 651
Kerberoasting
Attaque de mot de passe hors ligne qui demande des tickets de service Kerberos pour des comptes de service et casse la portion chiffree afin de retrouver le mot de passe en clair.
- attacks№ 886
Pass-the-Ticket
Attaque sur Active Directory qui rejoue un ticket Kerberos derobe afin d'usurper l'identite d'un utilisateur ou d'un service sans connaitre son mot de passe.
- attacks№ 836
Attaque NTLM Relay
Attaque de l'homme du milieu (MITRE T1557.001) ou un attaquant relaie l'authentification NTLM d'une victime vers un autre service pour usurper son identite sans connaitre son mot de passe.