Insufficient Verification of Data Authenticity

Summary

Tekton Pipelines project provides k8s-style resources for declaring CI/CD-style pipelines. In versions from 0.35.0, pipelines do not validate child UIDs, which means that a user that has access to create 'TaskRuns' can create their own Tasks that the Pipelines controller will accept as the child Task. While the software stores and validates the PipelineRun's (api version, kind, name, uid) in the child Run's 'OwnerReference', it only stores (api version, kind, name) in the 'ChildStatusReference'. This means that if a client had access to create 'TaskRuns' on a cluster, they could create a child 'TaskRun' for a pipeline with the same name + owner reference, and the Pipeline controller picks it up as if it was the original 'TaskRun'. This is problematic since it can let users modify the config of Pipelines at runtime, which violates SLSA L2 Service Generated / Non-falsifiable requirements. This issue can be used to trick the Pipeline controller into associating unrelated Runs to the Pipeline, feeding its data through the rest of the Pipeline. This requires access to create 'TaskRuns', so the impact may vary depending on one Tekton setup. If users already have unrestricted access to create any Task/PipelineRun, this does not grant any additional capabilities. As of the time of publication, there are no known patches for this issue.