CVE-2021-21670 in Jenkins
Summary
by MITRE • 07/01/2021
Jenkins 2.299 and earlier, LTS 2.289.1 and earlier allows users to cancel queue items and abort builds of jobs for which they have Item/Cancel permission even when they do not have Item/Read permission.
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Analysis
by VulDB Data Team • 07/04/2021
This vulnerability exists in Jenkins versions up to 2.299 and LTS versions up to 2.289.1 where the permission system exhibits a logical flaw in access control enforcement. The issue stems from a misconfiguration in the authorization model that allows users with Item/Cancel permission to manipulate queue items and abort builds without possessing the required Item/Read permission. This represents a classic case of insufficient authorization checking where the system fails to validate that users have appropriate read access before permitting destructive actions. The vulnerability falls under CWE-284 Access Control Bypass and aligns with ATT&CK technique T1078 Valid Accounts, as it exploits legitimate user permissions to perform unauthorized actions.
The technical flaw manifests when a user with Item/Cancel permission attempts to cancel queue items or abort builds. Normally, such operations should require both cancellation and read permissions to prevent unauthorized access to build information and resources. However, Jenkins fails to enforce the read permission check during these specific operations, creating a gap in the access control mechanism. This oversight allows malicious or unauthorized users to disrupt build processes and potentially gain insights into job configurations or build artifacts without proper authorization. The vulnerability particularly affects continuous integration environments where build stability and security are paramount.
The operational impact of this vulnerability extends beyond simple disruption of build processes. Attackers could potentially use this flaw to interfere with critical build pipelines, causing delays or failures in deployment processes. More concerning is the potential for information leakage where canceling builds might expose sensitive build parameters or configuration details that would normally be protected by read permissions. Organizations relying on Jenkins for automated workflows face significant risks including build process manipulation, potential denial of service conditions, and unauthorized access to sensitive project information. The vulnerability particularly affects environments where Jenkins is used for security-sensitive applications or compliance-critical builds.
Mitigation strategies should begin with immediate upgrades to Jenkins versions 2.300 or later where this vulnerability has been addressed through proper authorization enforcement. Organizations should conduct comprehensive permission audits to identify users with Item/Cancel permissions that may be exploited. Implementing additional security controls such as role-based access control restrictions and monitoring for unusual cancellation activities can provide additional layers of protection. The fix implemented by Jenkins developers ensures proper permission validation before allowing build cancellation or queue manipulation, addressing the root cause by enforcing the required Item/Read permission during these operations. Regular security assessments and adherence to security best practices including principle of least privilege should be maintained to prevent similar authorization bypass vulnerabilities in the future.