Kerberos Constrained Delegation
O que é 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.
● Exemplos
- 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.
● Perguntas frequentes
O que é 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. Pertence à categoria Identidade e acesso da cibersegurança.
O que significa 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.
Como funciona 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.
Como se defender contra Kerberos Constrained Delegation?
As defesas contra Kerberos Constrained Delegation costumam combinar controles técnicos e práticas operacionais, conforme detalhado na definição acima.
Quais são outros nomes para Kerberos Constrained Delegation?
Nomes alternativos comuns: KCD, Resource-Based Constrained Delegation, RBCD.
● Termos relacionados
- identity-access№ 652
Kerberos
Protocolo de autenticação de rede baseado em tickets que utiliza criptografia simétrica e um Centro de Distribuição de Chaves confiável para oferecer SSO seguro entre serviços.
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Active Directory
Serviço de diretório empresarial da Microsoft para redes Windows, que fornece autenticação, autorização e gestão de políticas centralizada para utilizadores, computadores e recursos.
- 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.
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Kerberoasting
Ataque offline de palavras-passe que solicita tickets de servico Kerberos para contas de servico e quebra a parte cifrada para recuperar as palavras-passe em claro.
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Pass-the-Ticket
Ataque ao Active Directory que reutiliza um ticket Kerberos roubado para se fazer passar por um utilizador ou servico sem conhecer a palavra-passe.
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Ataque de NTLM Relay
Ataque adversary-in-the-middle (MITRE T1557.001) em que o atacante encaminha a autenticacao NTLM de uma vitima a outro servico para se passar por ela sem saber a senha.