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Jenkins Token

A Jenkins token is a credential used to authenticate users or systems to a Jenkins server, which is a popular open-source automation server used for continuous integration and continuous delivery (CI/CD). This token allows access to Jenkins' API and can be used to trigger builds, access job configurations, and manage Jenkins resources. Exposure of a Jenkins token is a significant security concern because it can lead to unauthorized access to the CI/CD pipeline, potentially compromising the entire software delivery process.

How Does It Look​

Jenkins tokens can appear in various contexts, such as:

  • Environment variables:

    export JENKINS_TOKEN="abc123xyz456"

  • Configuration files (YAML):

    jenkins:
      token: "abc123xyz456"

  • Code snippets:

    import requests

    headers = {"Authorization": "Bearer abc123xyz456"}
    response = requests.get("https://jenkins.example.com/api/json", headers=headers)

  • Connection strings:

    https://user:abc123xyz456@jenkins.example.com/job/my-job/build

Severity​

  • 🔴 Critical

The severity of a Jenkins token exposure is critical because it can provide full access to the Jenkins server, allowing an attacker to manipulate CI/CD pipelines. This can lead to unauthorized code deployment, data exfiltration, and infrastructure compromise. The blast radius is extensive, potentially affecting all applications and environments managed by the Jenkins server.

What Can an Attacker Do?​

With immediate access to a Jenkins token, an attacker can control the Jenkins server and its resources.

Key actions an attacker can perform:

  • Trigger unauthorized builds (if the token has build permissions)
  • Access sensitive job configurations (if the token has read permissions)
  • Inject malicious code into the pipeline (if the token has write permissions)
  • Exfiltrate sensitive data (if the token allows access to job artifacts)

An attacker can escalate their access by modifying job configurations to include additional malicious steps or by deploying backdoors into the software being built. This lateral movement can compromise other systems integrated with Jenkins.

Real-World Impact​

Exposure of a Jenkins token poses significant business risks, including:

Potential consequences include:

  • Data Exposure: Access to sensitive build logs and artifacts (if the token has read access to job outputs)
  • Financial Loss: Unauthorized resource usage and potential downtime (if the attacker triggers resource-intensive builds)
  • Operational Disruption: Compromised software delivery pipeline (if the attacker modifies or deletes jobs)
  • Reputational Damage: Loss of trust from stakeholders and customers

In the worst-case scenario, an attacker could deploy malicious software to production environments, leading to widespread security breaches and data loss.

Prerequisites for Exploitation​

To exploit a Jenkins token, an attacker needs:

  • Network access to the Jenkins server
  • Knowledge of Jenkins endpoints and job names
  • No IP restrictions or MFA enforcement on the Jenkins server

How to Verify If It's Active​

To verify if a Jenkins token is active, use the following command:

curl -s -H "Authorization: Bearer [TOKEN]" https://jenkins.example.com/api/json

Valid credential response: A JSON response with Jenkins server details and job information.

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

Detection Patterns​

Common Variable Names:

  • JENKINS_TOKEN
  • JENKINS_API_TOKEN
  • JENKINS_AUTH_TOKEN
  • JENKINS_SECRET
  • JENKINS_CREDENTIALS
  • JENKINS_ACCESS_TOKEN

File Locations:

  • .env
  • config.yaml
  • jenkinsfile
  • settings.xml
  • credentials.json

Regex Pattern:

jenkins[_-]?token['"]?\s*[:=]\s*['"]?[a-zA-Z0-9]{32,}['"]?

Remediation Steps​

  1. Revoke immediately - Go to Jenkins > Manage Jenkins > Configure Global Security and delete the compromised token.
  2. Audit access logs - Review Jenkins access logs for unauthorized job triggers or configuration changes during the exposure window.
  3. Assess blast radius - Identify all jobs, pipelines, and environments that used the exposed token.
  4. Rotate credential - Generate a new Jenkins token with least-privilege permissions.
  5. Update dependent systems - Deploy the new token to all applications and update CI/CD pipelines securely.
  6. Harden access controls - Enable IP allowlisting in Jenkins and require multi-factor authentication (MFA) for access.
  7. Implement secrets management - Migrate tokens 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 token 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​