Canary Token is great…but beware of a flaw when using Thinkst’s free service for Canary AWS token

Introduction

Canary Token is a great idea for early detection of possible intrusion in your system.

But be careful when you are using the free service from Thinkst Canary (https://canarytokens.org/generate) to generate Canary AWS tokens. You shouldn’t use it for real life production.

A threat actor may notice a common pattern in the AWS access key id (generated from Thinkst Canary) and avoid triggering your honeypot detection.

AWS Access Key ID Format

Aidan Steele wrote an in-depth article on AWS Access Key ID format. Highly recommend to read it.

Things to note from Aidan’s article:

• The first 4 chars of the AWS Access Key will be indicate the resource types (https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_identifiers.html#identifiers-unique-ids)
• The next 8 chars of the access key will be mapped to a specific AWS account.

We can get the AWS account id from the access key by using the aws-cli

$ aws sts get-access-key-info --access-key-id <<ACCESS_KEY_ID>> --query Account --no-cli-pager
xxxxxxxxxxxxxxxxxxxxxxxxxxx

Flaws from the free service

Let’s generate a few Canary tokens from https://canarytokens.org/generate

[default]
aws_access_key_id = AKIAYVP4CIPPxxxxxxxU
aws_secret_access_key = xxxxxxxx
output = json
region = us-east-2

[default]
aws_access_key_id = AKIAYVP4CIPPxxxxxxxW
aws_secret_access_key = xxxxxxxxx
output = json
region = us-east-2

As you can see from the two generated Canary token, the four chars of the access key id show that this is an access key. Then the next crucial pattern (next 8 chars) will expose the information that this access key belongs to the AWS account from the free Canary token service.

A smart threat actor will detect this pattern and avoid using it. As a result, your Canary Token honeypot will likely to fail.

Takeaways

• Avoid using Canary Token services which provide predictable access key pattern. A threat actor can identify the pattern and avoid triggering the canary token.
• Canary Token is one of the detectors that we should use, but beware of confirmation biases (Canary token not triggered does not mean there is no intrusion).