Tags: 2022 mailman cloud 1337up-live-ctf kubernetes 

Rating: 3.5

The name word-played postman, a popular HTTP client used in web development. The UI allow to put in an URL, choose GET, POST method, set headers... like Postman.

First trying to access file://etc/passwd and got the file content, too easy? Then try all these files:

/proc/self/stat to know which user running, pid low number hints this run in a container.
/proc/self/cmdline to know the command used
/proc/self/cwd/app.py to read the code
/proc/self/cwd/app.ini to read the config

None of secret or flag there.

/proc/self/environ which might contain secret passed as environment, but got permission denied.

It seems stuck there.

Go back to About page, it advertised:

About Mailman

Mailman is a online HTTP client for developers to test their APIs. We provide a easy to use UI and the best user experience Best performance

At Mailman we garantee 100% uptime thanks to all of our services running in Kubernetes. And the best performance for our customers 100% secure!

We take our customer's security very seriously that is why we only use kubernetes secrets to store our most valued secrets.

use kubernetes (k8s) secrets to store our most valued secrets is the hint. We need to find kubernetes secrets. secret is an kubernetes object, which is intended to store secrets like key, password, but by default, it only stores secrets as base64.

The name of a Secret object must be a valid DNS subdomain name. You can specify the data and/or the stringData field when creating a configuration file for a Secret. The data and the stringData fields are optional. The values for all keys in the data field have to be base64-encoded strings. If the conversion to base64 string is not desirable, you can choose to specify the stringData field instead, which accepts arbitrary strings as values.

Now we find a way to access kubernetes secret from inside the container (often as ~ a pod in k8s terminology).

Like docker, or AWS EC2 instances, there are always some ways to access info from "outside", search Accessing the Kubernetes API from a Pod got https://kubernetes.io/docs/tasks/run-application/access-api-from-pod/

So each pod has these files contains info needed

/var/run/secrets/kubernetes.io/serviceaccount/token - used as Authentiation: bearer header
/var/run/secrets/kubernetes.io/serviceaccount/ca.crt - we not need here
/var/run/secrets/kubernetes.io/serviceaccount/namespace - to know which namespace is our container, this case is the default namespace.

The API can accessed via https://kubernetes.default.svc/api.

Go to each API path to discover until see secretstuff:


There the base64 encoded flag:



Original writeup (https://github.com/pymivn/ctf/blob/main/2022-1337UP-LIVE-CTF/mailman.md).