Gemini CLI on Windows: every git command fails with `fatal: unable to access 'NUL': Invalid argument` (Git for Windows 2.56.0 regression)

Context

Source(s): https://github.com/google-gemini/gemini-cli/issues/29614 (upstream: https://github.com/git-for-windows/git/issues/6449) Status: reported working by source, not reproduced by us.

Problem

When Gemini CLI runs git status, git log, git diff or any other git command through its shell tool on Windows, git aborts immediately with the error above.

Error (redacted / normalized)

fatal: unable to access 'NUL': Invalid argument

Applies when

Windows, Gemini CLI 0.62.0, Git for Windows 2.56.0 (the first 2.56 build, git version 2.56.0.windows.1 (our inference)).

Confirm it is this problem

1. git --version → expect: git version 2.56.0.windows.1 (our inference).
2. our inference: reproduce outside Gemini CLI in cmd with set GIT_CONFIG_GLOBAL=NUL followed by git status → expect the same fatal error.

Not this when / boundary

fatal: unable to access 'https://...' errors (network, proxy or credentials) are different problems. our inference: other tools that set GIT_CONFIG_GLOBAL=NUL on Windows may hit the same regression, and the same Git update should apply.

Root cause

Gemini CLI sanitizes the environment for its shell tool and sets GIT_CONFIG_GLOBAL to NUL on Windows (to /dev/null elsewhere). Git for Windows 2.56.0 introduced a regression where checking access to NUL returns "Invalid argument", so git stops before running the command. A commenter linked the upstream Git for Windows issue.

Fix

1. Update Git for Windows to <ip> or later (as the thread writes it; our inference: git --version then shows 2.56.0.windows.2). → expect: the original poster and two commenters confirmed this resolves it in Gemini CLI.
2. If you can't update yet, go back to Git for Windows 2.55.5 (suggested by a commenter).

How to verify

Ask Gemini CLI to run git status → expect: normal git output, no unable to access 'NUL'.

What did not work

none reported

Risks

our note: don't patch the CLI's installed bundle files; they get overwritten on the next update.

Verified scope

Git for Windows 2.56.0 (first build), Gemini CLI 0.62.x, October 2026.

Becomes obsolete when

2.56.0.windows.1 (our inference) is no longer in use.