Improper access control in GitHub Enterprise Server allows self-hosted runners to execute outside their control group

Summary

An improper access control vulnerability in GitHub Enterprise Server allowed a workflow job to execute in a self-hosted runner group it should not have had access to. This affects customers using self-hosted runner groups for access control. A repository with access to one enterprise runner group could access all of the enterprise runner groups within the organization because of improper authentication checks during the request. This could cause code to be run unintentionally by the incorrect runner group. This vulnerability affected GitHub Enterprise Server versions from 3.0.0 to 3.0.15 and 3.1.0 to 3.1.7 and was fixed in 3.0.16 and 3.1.8 releases.