GHSA-hmq2-w58f-27jc: GitPython: Arbitrary Git Repository Creation Outside the Working Tree via Unvalidated .gitmodules Submodule Name in GitPython

GitPython computes the on-disk location of a submodule’s separate Git directory (.git/modules/<name>) from the submodule’s .gitmodules section name with no validation. Because that name is fully attacker-controlled content of a cloned repository, a malicious repository can set a submodule name to a traversal string (e.g. ../../../../home/victim/.something) and cause GitPython to create and initialize a full Git repository at an attacker-chosen filesystem path outside the intended clone directory. The only precondition is that a victim clones the malicious repository with GitPython and runs submodule initialization (submodule_update(init=True) / sm.update(init=True)), a very common and often automatic step. Core Git itself already blocks this exact attack class (CVE-2018-11235), but GitPython’s independent reimplementation never adopted an equivalent check.