Dulwich's submodule path traversal in porcelain.submodule_update / porcelain.clone(recurse_submodules=True) yields RCE via attacker-dropped .git/hooks payload

Dulwich is a pure-Python implementation of the Git file formats and protocols. Starting in version 0.23.2 and prior to version 1.2.5, `dulwich.porcelain.submodule_update`, and by extension `porcelain.clone(..., recurse_submodules=True)`, materializes attacker-controlled submodule paths from a crafted upstream repository without path validation. A malicious `.gitmodules` plus a matching tree gitlink whose `path` is `.git/hooks` (or any other directory inside the parent repository's `.git` directory) causes the attacker's submodule tree contents to be written directly into the victim's `.git/hooks/` directory, preserving executable mode bits. The dropped executables are then run by any subsequent `git` or `dulwich` command that invokes the matching hook, resulting in arbitrary code execution. This is the dulwich equivalent of the upstream Git fixes for CVE-2024-32002 / CVE-2024-32004, which were never propagated into dulwich's separately implemented submodule porcelain. Version 1.2.5 patches the issue.