Two Old Oj Flaws Chained to Trigger GitLab Remote Code Execution

A researcher disclosed a remote code execution vulnerability in GitLab that chains two memory-safety flaws in the Ruby Oj JSON parser used by the ipynbdiff gem when processing Jupyter Notebook (.ipynb) diffs. The exploit allows an authenticated user with push and diff-view permissions to execute arbitrary commands as the git system user, potentially exposing repository source, Rails secrets, service credentials, and internal services; affected GitLab CE/EE and Oj gem versions are listed and fixes are available — self-managed instances should upgrade immediately.