AWS - KMS Persistence

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KMS

For mor information check:

AWS - KMS Enum

Grant acces via KMS policies

An attacker could use the permission kms:PutKeyPolicy to give access to a key to a user under his control or even to an external account. Check the KMS Privesc page for more information.

Eternal Grant

Grants are another way to give a principal some permissions over a specific key. It's possible to give a grant that allows a user to create grants. Moreover, a user can have several grant (even identical) over the same key.

Therefore, it's possible for a user to have 10 grants with all the permissions. The attacker should monitor this constantly. And if at some point 1 grant is removed another 10 should be generated.

(We are using 10 and not 2 to be able to detect that a grant was removed while the user still has some grant)

bash
# To generate grants, generate 10 like this one
aws kms create-grant \
    --key-id <key-id> \
    --grantee-principal <user_arn> \
    --operations "CreateGrant" "Decrypt"

# To monitor grants
aws kms list-grants --key-id <key-id>

note

A grant can give permissions only from this: https://docs.aws.amazon.com/kms/latest/developerguide/grants.html#terms-grant-operations

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