Attack Chain

1. Compromise Account: An attacker gains unauthorized access to a CircleCI account with sufficient privileges to modify project settings.
2. Identify Security Steps: The attacker enumerates the defined security steps within the CircleCI configuration files (e.g., .circleci/config.yml).
3. Modify Configuration: The attacker modifies the CircleCI configuration files to disable specific security steps, such as vulnerability scanning, code analysis, or secret scanning.
4. Commit Changes: The attacker commits the modified configuration files to the project's repository.
5. Trigger Build: The changes trigger a new build in CircleCI, which now executes without the disabled security steps.
6. Deploy Malicious Code (Optional): If the disabled security steps were intended to prevent the introduction of malicious code, the attacker may now introduce it without immediate detection.
7. Exfiltration (Optional): If the disabled security steps were intended to prevent data exfiltration, the attacker can now potentially exfiltrate sensitive data.
8. Maintain Persistence: The attacker might create backdoors or alter other configurations to maintain long-term access and control over the CI/CD pipeline.

Impact

A successful attack involving the disabling of security steps in CircleCI can lead to the introduction of vulnerabilities into production systems, data breaches, and supply chain attacks. The impact can range from defacement of websites to complete compromise of critical infrastructure. The number of victims can vary depending on the scope of the compromised CI/CD pipeline, from a single internal application to a widely distributed software product affecting thousands of users.

Recommendation

• Implement multi-factor authentication (MFA) for all CircleCI accounts to mitigate account compromise (reference: any CircleCI documentation on MFA).
• Monitor CircleCI audit logs for configuration changes that disable security-related steps (reference: CircleCI audit log documentation, implement detections based on modifications of .circleci/config.yml).
• Implement the Sigma rule Detect CircleCI Configuration Changes to detect modifications of CircleCI config files.
• Implement the Sigma rule Detect CircleCI Disable Security Step to detect disabling of security steps based on modifications to .circleci/config.yml.

Attack Chain

1. Initial Access: The attacker gains access to the CircleCI project's configuration, potentially through compromised credentials or a vulnerability in the CircleCI platform itself.
2. Configuration Modification: The attacker modifies the .circleci/config.yml file to remove or comment out security-related steps. This could include steps that run static analysis tools, vulnerability scanners, or code quality checks.
3. Bypass Security Checks: With the security steps disabled, the build pipeline no longer enforces the intended security controls.
4. Code Injection: The attacker introduces malicious code into the codebase, either directly or through a compromised dependency. This code could be designed to steal secrets, create backdoors, or perform other malicious activities.
5. Automated Build and Deployment: The modified code is automatically built and deployed through the CI/CD pipeline.
6. Compromise Production Environment: The malicious code is deployed to the production environment, allowing the attacker to gain unauthorized access to systems and data.

Impact

Successful disabling of security steps in CircleCI can lead to significant consequences. An attacker could inject malicious code into production systems, potentially affecting thousands of users and causing severe financial and reputational damage. Stolen credentials, backdoors, and data breaches could be used for further attacks or sold on the dark web. The targeted sectors are broad, including any organization using CircleCI for software development, particularly those in sensitive industries like finance and healthcare. The impact could range from data theft and service disruption to complete system compromise.

Attack Chain

1. Initial Access: The attacker gains unauthorized access to a CircleCI user account or acquires sufficient permissions to modify pipeline configurations.
2. Reconnaissance: The attacker identifies mandatory security jobs within the CircleCI workflows using the CircleCI UI or API, noting the workflow_name and associated job_name.
3. Configuration Modification: The attacker modifies the CircleCI pipeline configuration (likely via the .circleci/config.yml file) to disable or bypass the identified mandatory security jobs. This might involve commenting out the job definition, removing it from the workflow, or adding conditions that prevent its execution.
4. Code Commit: The attacker commits the modified configuration file to the associated Git repository, triggering a new pipeline execution. The vcs.url field provides the URL to the commit and related changes.
5. Bypassed Security Checks: The pipeline executes without running the mandatory security jobs, allowing potentially malicious code to proceed through the CI/CD process unchecked.
6. Deployment: The unchecked code is deployed to staging or production environments.
7. Impact: Depending on the nature of the malicious code, the impact could include data breaches, system compromise, or service disruption.

Impact

The successful disabling of security jobs in CircleCI can have significant consequences. A single compromised pipeline could lead to the introduction of vulnerable code into production, impacting thousands of users and critical infrastructure. Potential damage includes data breaches, system downtime, reputational damage, and financial loss. Organizations in all sectors utilizing CircleCI for their CI/CD processes are at risk.

Recommendation

• Deploy the provided Sigma rule to detect instances where mandatory security jobs are not executed within CircleCI workflows; tune the rule for your environment.
• Investigate alerts triggered by the Sigma rule, focusing on the user and the specific workflow_name where the security job was disabled.
• Review CircleCI access logs for suspicious account activity that might indicate unauthorized access.
• Implement multi-factor authentication (MFA) for all CircleCI user accounts to reduce the risk of account compromise.

Attack Chain

1. Account Compromise/Privilege Escalation: The attacker gains unauthorized access to a CircleCI account or escalates privileges within a legitimate account. This could be achieved through phishing, credential stuffing, or exploiting vulnerabilities in the CircleCI platform itself.
2. Authentication: The attacker authenticates to the CircleCI platform using compromised credentials or a session token.
3. Project Enumeration: The attacker enumerates the projects and pipelines available within the CircleCI environment to identify targets of interest.
4. Security Job Identification: The attacker identifies specific CircleCI jobs responsible for security-related tasks, such as SAST, DAST, or dependency scanning.
5. Job Configuration Modification: The attacker modifies the configuration of the targeted security jobs. This could involve disabling the job entirely, removing it from the pipeline, or altering its execution parameters to bypass security checks.
6. Code Integration (Optional): The attacker introduces malicious code into the build process. This step is not directly related to the job disablement, but is its likely motivation.
7. Pipeline Execution: A build pipeline is triggered, now skipping the disabled security jobs and potentially integrating the malicious code into the final artifact.
8. Deployment: The compromised artifact is deployed to production, resulting in a security breach.

Impact

A successful attack could allow an attacker to introduce malicious code into a software product, leading to widespread compromise of systems and data. The impact includes data breaches, service disruptions, and reputational damage. The specific number of victims depends on the reach of the compromised software. Organizations in various sectors relying on CircleCI for CI/CD are potential targets.

Recommendation

• Implement the "Detect CircleCI Security Job Disablement" Sigma rule to detect unauthorized modifications to CircleCI job configurations.
• Enable detailed audit logging within CircleCI to capture all configuration changes and API requests. Analyze these logs for suspicious activity.
• Enforce multi-factor authentication (MFA) for all CircleCI accounts, especially those with administrative privileges.
• Review and restrict CircleCI API token permissions to follow the principle of least privilege.
• Regularly review CircleCI project configurations and user permissions to identify and remediate any unauthorized changes.
• Utilize CircleCI's built-in security features, such as context variables and IP whitelisting, to further restrict access and prevent unauthorized modifications.
• Investigate any alerts generated by the "Detect CircleCI Security Job Disablement" Sigma rule promptly to identify and mitigate potential security breaches.