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Buildkite API Key

Buildkite is a continuous integration and delivery platform that allows developers to automate their software testing and deployment processes. An API key for Buildkite is a credential that grants access to the Buildkite API, enabling users to interact programmatically with their Buildkite pipelines, jobs, and other resources. Exposure of this API key is a significant security concern as it can lead to unauthorized access to sensitive build and deployment processes, potentially compromising the integrity and confidentiality of the software being developed.

How Does It Look​

Buildkite API keys can appear in various contexts, such as:

  • Environment variables:

    export BUILDKITE_API_KEY="bk1234567890abcdef"

  • Configuration files (YAML):

    buildkite:
      api_key: "bk1234567890abcdef"

  • Code snippets:

    import os

    api_key = os.getenv("BUILDKITE_API_KEY")

  • Connection strings:

    https://api.buildkite.com/v2/organizations/[ORG]/pipelines?access_token=bk1234567890abcdef

Severity​

  • 🔴 Critical

The severity of a Buildkite API key exposure is critical because it provides access to the Buildkite API, which can control build and deployment processes. An attacker with this key can manipulate pipelines, access sensitive build logs, and potentially inject malicious code into the software development lifecycle. The blast radius includes all projects and environments managed by the Buildkite account.

What Can an Attacker Do?​

With immediate access to a Buildkite API key, an attacker can perform several malicious actions:

  • Modify pipelines: Change build configurations or scripts (if the credential has write permissions).
  • Access sensitive logs: View build logs that may contain proprietary or sensitive information (if logging is enabled).
  • Inject malicious code: Alter build scripts to include harmful code (if the attacker can modify pipeline steps).
  • Disrupt operations: Cancel or rerun builds, causing delays or failures in the deployment process (if build control permissions are granted).

An attacker could also escalate their access by leveraging the compromised API key to explore other connected systems or services, potentially leading to broader network infiltration.

Real-World Impact​

The exposure of a Buildkite API key poses significant business risks, including:

  • Data Exposure: Access to build logs and configurations (if the credential has read access to sensitive data).
  • Financial Loss: Costs associated with unauthorized resource usage or downtime (if billing/resource creation is permitted).
  • Operational Disruption: Interruptions in the software development lifecycle (if the attacker has delete/modify permissions).
  • Reputational Damage: Loss of trust from clients and stakeholders due to compromised software integrity.

In a worst-case scenario, the exposure could lead to widespread software vulnerabilities being introduced into production environments, affecting end-users and damaging the organization's reputation.

Prerequisites for Exploitation​

To exploit a Buildkite API key, an attacker needs:

  • Network access: Ability to send requests to the Buildkite API endpoint.
  • Additional context: Knowledge of the organization ID or pipeline names to target specific resources.
  • No rate limits: Exploitation is easier if there are no strict rate limits or IP restrictions in place.

How to Verify If It's Active​

To verify if a Buildkite API key is active, use the following command:

curl -H "Authorization: Bearer [API_KEY]" https://api.buildkite.com/v2/organizations/[ORG]/pipelines

Valid credential response: A list of pipelines in JSON format, indicating successful authentication.

Invalid/expired credential response: An error message indicating unauthorized access or invalid token.

Detection Patterns​

Common Variable Names:

  • BUILDKITE_API_KEY
  • BUILDKITE_TOKEN
  • BK_API_KEY
  • BK_TOKEN
  • BUILDKITE_ACCESS_TOKEN
  • BUILDKITE_SECRET

File Locations:

  • .env
  • config.yml
  • settings.json
  • buildkite.yml
  • credentials.txt

Regex Pattern:

bk[a-zA-Z0-9]{16,40}

Remediation Steps​

  1. Revoke immediately - Go to Buildkite > Settings > API Access and delete the compromised API key.
  2. Audit access logs - Review Buildkite audit logs for unauthorized pipeline changes or access during the exposure window.
  3. Assess blast radius - Identify all systems, applications, and environments that used the exposed credential.
  4. Rotate credential - Generate a new API key in Buildkite with least-privilege permissions.
  5. Update dependent systems - Deploy the new credential to all applications and update CI/CD pipelines securely.
  6. Harden access controls - Enable IP allowlisting in Buildkite and require two-factor authentication for all users.
  7. Implement secrets management - Migrate credentials to a secrets manager (HashiCorp Vault, AWS Secrets Manager) to prevent hardcoding.
  8. Add detection controls - Set up pre-commit hooks and repository scanning to catch credential leaks before they reach production.

Credential exposures often go undetected for extended periods, increasing the window for exploitation. As a long-term strategy, plan to establish an internal process or engage an external vendor for continuous external exposure monitoring. This helps identify leaked secrets across public repositories, paste sites, dark web forums, and other external sources before attackers can leverage them. Proactive detection and rapid response are essential to minimizing the impact of credential leaks.

References​