Thursday, May 28, 2020

Deployment time security audit using CloudFormation custom resource.

To prevent deployment of the potentially sensitive resources or infrastructure into the AWS account that might not meet current organizational security standard we can use AWS CloudFormation custom resource to perform quick security audit (or kind of sanity check) of the cloud account before processing with deployment.

Why we need this if we can scan/audit account as a part of the CI/CD pipeline? For the cases when deployments are performed manually or to have CI/CD independent "portable" CloudFormation template that has all security checks built-in and not bolt-on.

How it will look like:

  1. To you normal CloudFormation template you will add a custom resource.
  2. This custom resource it technically speaking a Lambda function that created and called during CloudFormation stack deployment.
  3. This Lambda function will perform quick (to meet CloudFormation deployment timeouts restrictions) security audit of the account where template going to be deployed
  4. As result of this audit Lambda will return status that will be interpreted by CloudFormation as a resource creation outcome.
  5. If AWS environment pass security check - deployment of other resources in you stack continue as usual
  6. If AWS environment fail security check - stack deployment will interrupted and rolled back as a result of the custom resource failure. 
I will publish example on such functionality on my Github shorty and will update this post with more details. 

Sunday, May 24, 2020 new version - now with vulnerability scan

Now service:
  • Does full port and vulnerability scan of the caller's IP
  • Immediately perform and return tcp scan results. Starts vulnerability scan in background.
  • Visit again in about 30min(depends on load), and results of the vulnerability scan (port, service, vulnerability, CVE) for you IP will be displayed. 
  • You can use, console friendly endpoint : , or
  •  use a human readable website:
Scan results examples:

Good  scan results:

Not so good scan  results:

As previously service is built using AWS native capabilities, serverless and containerized approach and design to be extremely scalable.

Quick FAQ:

What's new? Now it does full vulnerability scan of the IP.

What it does? Scan your external IP for open TCP ports and known vulnerabilities.
How to use? Simply do _curl scan.nmap.me_ from your console/terminal or open this webite in browser. You will get TCP scan results immediately and you will need to visit same page in an hour to get vulnerability scan results.

What it's scanning for?: Uses nmap NSE script to perform scan for known vulnerabilities. Based on

How fast? Whole TCP scan takes about a few second and results are immediately shown. After this vuln scan is starting. Depending of the backend load it might take about an hour to get scanned. After this simply visit the same page again to get vulnerability scan results. Scan results for each requester IP are cached for 1 hour (TCP scan) and 24 hours (Vuln scan) to reduce load and prevent abuse.

Friday, May 15, 2020

Using MFA with AWS CLI

It quite obvious nowadays that you must use MFA if it's available.
Enabling MFA for your user account in AWS IAM will automatically enforce it for the AWS Web UI login. 

But what about AWS CLI, your code using AWS SDK and 3d party SDK based tools?
In this case, to leverage MFA you need to enforce it using "Condition" statement for the IAM policy assigned to you user as it described in following AWS manual:

In nutshell something like this:

Enforce MFA for the assume role:
{ "Version": "2012-10-17", "Statement": [ { "Sid": "", "Effect": "Allow", "Principal": { "AWS": "arn:aws:iam::123456789012:user/anika" }, "Action": "sts:AssumeRole", "Condition": { "Bool": { "aws:multifactorAuthPresent": true } } } ] }

Add MFA to you AWS CLI profile:

[profile role-with-mfa] region = us-west-2 role_arn= arn:aws:iam::128716708097:role/cli-role source_profile = cli-user mfa_serial = arn:aws:iam::128716708097:mfa/cli-user

Simple? Not exactly - here some tricky things that not covered by AWS documentation (at least I was not able to find).

1. AWS documentation a bit misleading: in the AIM statement and documentation user name  mentioned is Anika but all CLI configs are pointing to the non existing cli profile "cli-user"

2. AWS CLI MFA configuration will work ONLY when you are assuming Role. Yep, if you have one simple account, few users  and groups (as many small companies do) you can't leverage this functionality without some small trick(item 3)

3. You can still leverage MFA with CLI using role:

  • Strip all access from the user you are using to login, except "assume role", or alternatively,  enforce the MFA for all the actions using condition from the above.  
If you will strip all permissions you will need to assume role even if you are using WEB UI.
If you use alternative approach and enforce MFA for all API actions you can keep using WEB UI without assuming role the same way as you was doing before.
  • Create a role (exampe: MyOrganizationAccountAccessRole) to assume in the same account with MFA enforced and all required access rights. If you have more than one account - create this role in other accounts as well with the same MFA enforcement condition.
  • Create extra profile my-account-mfa (in addition to the main account profile my_account ) for the accessing the same account (my-account) using this role: 
[profile my-account-mfa]
role_arn = arn:aws:iam:: 123456789:role/MyOrganizationAccountAccessRole
source_profile = my_account
mfa_serial = arn:aws:iam:: 123456789:mfa/it-security@ca

[profile my_account]
output = json
region = us-east-1
mfa_serial = arn:aws:iam::123456789:mfa/it-security@ca

[profile my_second_account]
ole_arn = arn:aws:iam:: 987654321:role/MyOrganizationAccountAccessRole
source_profile = my_account
mfa_serial = arn:aws:iam:: 123456789:mfa/it-security@ca

Note : all profile reference  my_account profile as a source

If needed create an extra profile(my_second_account) for any other account you need to access using the role.

Use  profile  my-account-mfa for you CLI access to the main account or for any tools. You will see MFA request and after providing MFA everything will work like a charm.

Enjoy and stay secure!