[Security] Harden CLI dev command against injection on Windows #1904
+9
−1
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
RinZ27
force-pushed
the
fix/windows-command-injection-v2
branch
2 times, most recently
from
f7b9f72 to
a63bde1
Compare
Kludex
reviewed
Jan 23, 2026
src/mcp/cli/cli.py
Outdated
Comment on lines
279
to
284
| cmd_args = [npx_cmd, "@modelcontextprotocol/inspector"] + uv_cmd | ||
|
|
||
| if shell: | ||
| # On Windows with shell=True, I need to quote arguments to prevent injection | ||
| # and join them into a single string, as passing a list with shell=True is unsafe/undefined behavior | ||
| cmd_args = " ".join(shlex.quote(arg) for arg in cmd_args) |
Member
There was a problem hiding this comment.
Can't we apply shlex on the whole thing? we don't need to check if shell, do we?
RinZ27
force-pushed
the
fix/windows-command-injection-v2
branch
from
a63bde1 to
4f4dba9
Compare
Contributor
Author
|
@Kludex I can't apply it universally because on POSIX I'm using Also, I realized |
I noticed that shlex.quote uses single quotes which cmd.exe doesn't handle correctly. Switched to list2cmdline to ensure proper escaping when shell=True is used on Windows. Also removed the unused shlex import.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
I was looking through the CLI code and spotted a potential security risk when using the
mcp devcommand on Windows. Becauseshell=Trueis required fornpx, passing raw arguments can lead to command injection if a user provides a file path containing shell metacharacters.I decided to use
shlex.quoteto sanitize these arguments before they are joined into the final command string. This way, I ensure that any special characters are safely escaped, keeping the execution restricted to the intended command. I've verified the fix and it correctly handles paths with spaces and other characters.