Kerberos Constrained Delegation
Что такое 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.
● Примеры
- 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.
● Частые вопросы
Что такое 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. Относится к категории Идентификация и доступ в кибербезопасности.
Что означает 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.
Как работает 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.
Как защититься от Kerberos Constrained Delegation?
Защита от Kerberos Constrained Delegation обычно сочетает технические меры и операционные практики, как описано в определении выше.
Какие есть другие названия Kerberos Constrained Delegation?
Распространённые альтернативные названия: KCD, Resource-Based Constrained Delegation, RBCD.
● Связанные термины
- identity-access№ 652
Kerberos
Сетевой протокол аутентификации на основе билетов, использующий симметричную криптографию и доверенный центр распределения ключей для безопасного единого входа.
- identity-access№ 014
Active Directory
Корпоративная служба каталогов Microsoft для сетей Windows, обеспечивающая централизованную аутентификацию, авторизацию и управление политиками для пользователей, компьютеров и ресурсов.
- 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
Оффлайн-атака на пароли: запрос Kerberos-билетов служб для сервисных учёток и взлом их зашифрованной части для восстановления паролей в открытом виде.
- attacks№ 886
Pass-the-Ticket
Атака на Active Directory: повторное использование украденного Kerberos-билета для имперсонации пользователя или службы без знания пароля.
- attacks№ 836
Атака NTLM Relay
Атака «человек посередине» (MITRE T1557.001), в которой злоумышленник пересылает NTLM-аутентификацию жертвы другому сервису и выдаёт себя за неё, не зная пароля.