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Comment by ldoughty | Hacker News Reader

I really dislike that the solutions for AWS tag shortcomings is custom code.

I'm a big AWS fan and heavy user for 5 years now, but it seems silly to me that you need to write a custom wrapper (e.g. force the creation through a managed script/template like Terraform/Ansible/CF)... Or write reactionary cloud trail policies to handle a situation where someone launches an EC2 instance without providing a specific tag.

The fact IAM policies still can't deny requests missing a tag, or deny requests by tag-value condition seems silly to me... Or one step further: allowing some auto-populated tags like what principle was responsible for making the instance in the first place.

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FYI, IAM policies do support tag-based access control: https://docs.aws.amazon.com/IAM/latest/UserGuide/access_tags.... This was introduced in the past 1-2 years.

That is access control when tags exist...

You can't, for example, deny an EC2 instance creation of it is NOT tagged with Key X. The recommendation is to watch cloud trail and post-creation, terminate it.

Creation events for EC2 do. It support tags, it's actually a 2 step process (the GUI console hides this, the SDK and IAM policy limits make this clear)

Ah, what you're looking for is SCP (service control policies). And AWS even has a handy example for denying creation when a tag is missing: https://docs.aws.amazon.com/organizations/latest/userguide/o...

> The fact IAM policies still can't deny requests missing a tag, or deny requests by tag-value condition seems silly to me...

Am I missing something here? I could have sworn that aws:RequestTag with a “Tag On Create” Actions would enforce the authorization check based on the in the Tags parameter? Similarly aws:TagKeys allows you to control the permitted values of those Tags.

> allowing some auto-populated tags like what principle was responsible for making the instance in the first place.

These do exist as “system tags”, but its on a per service basis. Migration Hib and ECS come to mind. I dont know of any cross cutting application (like IAM) where theyre applied universally.

https://docs.aws.amazon.com/IAM/latest/UserGuide/access_tags... https://docs.aws.amazon.com/IAM/latest/UserGuide/access_tags... https://aws.amazon.com/about-aws/whats-new/2020/04/aws-migra...

> The fact IAM policies still can't deny requests missing a tag, or deny requests by tag-value condition seems silly to me...

Can't it, though?

  "Condition": {
    "StringEquals": {
      "aws:RequestTag/key1": "value1",
      "aws:RequestTag/key2": "value2"
    },
    "ForAllValues:StringEquals": {
      "aws:TagKeys": [
        "key1",
        "key2"
      ]
    }
  }

The problem is that all IAM conditionals just give a generic "Denied" statement which is hard to debug. You at left figuring out if you are missing a uppercase character in your tag key. AWS IAM is currently not meant to be used in a devops/enforcement of best practices way. They have AWS config for that, but that's always after the fact while immediate feedback is what you need to function at scale.

A possible fix is to allow custom deny reasons but large changes like this to any already extremely large and entangled system like IAM is unlikely.

> "A possible fix is to allow custom deny reasons but large changes like this to any already extremely large and entangled system like IAM is unlikely."

This would allow an attack to enumerate permissions by seeing what's denied.

Generic statements aren't a bug, they're a feature.

Yes, but what they're talking about isn't a security denial but a configuration check. Can you imagine if the only output to a git commit pre-hook was "no" and you were left to figure out why?

> "Yes, but what they're talking about isn't a security denial but a configuration check."

Configuration is a part of security though.

Let's say AWS credentials are leaked. One of the most common uses for leaked credentials is to launch EC2 instance for crypto mining. A malicious actor tries to launch RunInstances on $20k worth of instances and gets denied because there isn't a tag on the instances. Would you want the error to say 'Access denied because you didn't don't have the following tag...'?

Yes, because lacking a tag isn't a security boundary. The account has permission to launch EC2 instances and knowing that instances need to have tags isn't a password designed to keep malicious actors out, it's a safeguard.

I feel like this is not a complex problem. You just ensure that someone has `iam:GetDetailedError`. Then you can turn it on for your role/user/whatever and if that doesn't work you can turn it on at the global level temporarily.

After all, if you think about it, if you are unable to determine that you're denying the person for the right reason, you could easily later allow them for the wrong reason.

e.g. A policy that's not meant to be applied to some IAM user is being applied to them but it's documented to be for a different purpose. When that purpose expires, you might remove that policy, and accidentally enable access. If you can get a trace of the denial then you know that it's for the right reasons.

Kinda, but it isn't consistent.

They've been steadily improving/fixing it, but for some resources, tagging new resources via the console is a 2 step process - it creates the resource THEN adds the tags. They are fixing these things so it's all added at once.

What this does is block the ability to create some resources via console since you can't add tags at creation

This is also a problem when using CloudFormation. CloudFormation will often create resources without tags and then add the tags in a separate call.

That's the root of my complaint...

This effectively means IAM cannot limit creation events by tag because it's two steps. Only solution is two steps

EC2, last I checked, does not allow tag conditionals at instance creation. You can have tag controls afterwards, but the instance creation call does not support tagging (the GUI masks this)

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