IAM Tools

ArnNotLikeIfExists

ArnNotLikeIfExists compares an ARN in a request to a list of ARN patterns in your policy. The policy values can include asterisks (*) to match multiple characters and question marks (?) to match a single character within an ARN segement. Wildcards cannot be used to span ARN segment, so the partition, service, region, account, and resource must all be present in your policy value, even if they are all wildcards. The comparision is case sensitive.

To match a request, the context key can be absent, but if present it must NOT match any of the ARN patterns in your policy.

You can use policy variables in the value of this operator.

So you know:

ArnNotLikeIfExists behaves exactly the same as ArnNotLike. "Negative" operators such as ArnNotLike already match requests if the key is not present so the IfExists suffix has no effect.

There is no harm in adding IfExists to ArnNotLike; it probably makes the intent more clear. We know you already knew this, but put this message in for everyone else. 😉

ArnNotLikeIfExists in an Allow Statement

Click into any of these polices and change them test how they change the result.

Given the Policy Condition:

"ArnNotLikeIfExists": {
  "aws:PrincipalArn": [
    "arn:aws:iam::*:role/*",
    "arn:aws:ec2:*:*:instance/i-?????"
  ]
}

When the Request Context has:

aws:PrincipalArn: null

Then the result is:

Allowed Assuming no explicit Deny elsewhere

Given the Policy Condition:

"ArnNotLikeIfExists": {
  "aws:PrincipalArn": [
    "arn:aws:iam::*:role/*",
    "arn:aws:ec2:*:*:instance/i-?????"
  ]
}

When the Request Context has:

aws:PrincipalArn: 
    arn:aws:iam::*:user/User

Then the result is:

Allowed Assuming no explicit Deny elsewhere

Given the Policy Condition:

"ArnNotLikeIfExists": {
  "aws:PrincipalArn": [
    "arn:aws:iam::*:role/*",
    "arn:aws:ec2:*:*:instance/i-?????"
  ]
}

When the Request Context has:

aws:PrincipalArn: 
    arn:aws:iam::123456789012:role/AdminRole

Then the result is:

Not Allowed Statement does not apply

ArnNotLikeIfExists in a Deny Statement

Click into any of these polices and change them test how they change the result.

Given the Policy Condition:

"ArnNotLikeIfExists": {
  "aws:PrincipalArn": [
    "arn:aws:iam::*:role/*",
    "arn:aws:ec2:*:*:instance/i-?????"
  ]
}

When the Request Context has:

aws:PrincipalArn: null

Then the result is:

Denied

Given the Policy Condition:

"ArnNotLikeIfExists": {
  "aws:PrincipalArn": [
    "arn:aws:iam::*:role/*",
    "arn:aws:ec2:*:*:instance/i-?????"
  ]
}

When the Request Context has:

aws:PrincipalArn: 
    arn:aws:iam::*:user/User

Then the result is:

Denied

Given the Policy Condition:

"ArnNotLikeIfExists": {
  "aws:PrincipalArn": [
    "arn:aws:iam::*:role/*",
    "arn:aws:ec2:*:*:instance/i-?????"
  ]
}

When the Request Context has:

aws:PrincipalArn: 
    arn:aws:iam::123456789012:role/AdminRole

Then the result is:

Not Denied May be allowed by another statement