Impact

When cloning a repository Git knows to optionally fetch a bundle advertised by the remote server, which allows the server-side to offload parts of the clone to a CDN. The Git client does not perform sufficient validation of the advertised bundles, which allows the remote side to perform protocol injection.

This protocol injection can cause the client to write the fetched bundle to a location controlled by the adversary. The fetched content is fully controlled by the server, which can in the worst case lead to arbitrary code execution.

Workarounds

The use of bundle URIs is not enabled by default and can be controlled by the bundle.heuristic config option. The problem can thus be avoided by disabling this config.

Some cases of the vulnerability require that the adversary is in control of where a repository will be cloned to. This either requires social engineering or a recursive clone with submodules. These cases can thus be avoided by disabling recursive clones.