Overview

On many platforms, a third party can create a Git repository under a name that includes a shell command substitution ¹ string in the syntax $(<command>). These directory names are allowed in macOS and a majority of Linux distributions ². If a user starts jupyter-lab in a parent directory of this inappropriately-named Git repository, opens it, and clicks "Git > Open Git Repository in Terminal" from the menu bar, then the injected command <command> is run in the user's shell without the user's permission.

This issue is occurring because when that menu entry is clicked, jupyterlab-git opens the terminal and runs cd <git-repo-path> through the shell to set the current directory ³. Doing so runs any command substitution strings present in the directory name, which leads to the command injection issue described here. A previous patch provided an incomplete fix ⁴.

Scope of Impact

This issue allows for arbitrary code execution via command injection. A wide range of actions are permitted by this issue, including but not limited to: modifying files, exfiltrating data, halting services, or compromising the server's security rules.

We have scanned the source code of jupyterlab-git for other command injection risks, and have not found any at the time of writing.

This issue was reproduced on the latest release of jupyterlab-git, v0.51.0. The steps taken to reproduce this issue are described in the "Proof-of-concept" section below.

Proof-of-concept

1. Create a new directory via mkdir test/ && cd test/.

2. Create a new Git repository under test/ with a command substitution string in the directory name by running these commands:

mkdir '$(touch pwned.txt)'
cd '$(touch pwned.txt)/'
git init
cd ..

3. Start JupyterLab from test/ by running jupyter lab.
4. With JupyterLab open in the browser, double click on $(touch pwned.txt) in the file browser.
5. From the top menu bar, click "Git > Open Git Repository in Terminal".
6. Verify that pwned.txt is created under test/. This demonstrates the command injection issue described here.

Proof-of-concept mitigation

The issue can be mitigated by the patch shown below.

diff --git a/src/commandsAndMenu.tsx b/src/commandsAndMenu.tsx
index 3779a6c..71ddcea 100644
--- a/src/commandsAndMenu.tsx
+++ b/src/commandsAndMenu.tsx
@@ -164,31 +164,13 @@ export function addCommands(
     label: trans.__('Open Git Repository in Terminal'),
     caption: trans.__('Open a New Terminal to the Git Repository'),
     execute: async args => {
-      const main = (await commands.execute(
-        'terminal:create-new',
-        args
-      )) as MainAreaWidget<ITerminal.ITerminal>;
+      const cwd = gitModel.pathRepository;
+      const main = (await commands.execute('terminal:create-new', {
+        ...args,
+        cwd
+      })) as MainAreaWidget<ITerminal.ITerminal>;
 
-      try {
-        if (gitModel.pathRepository !== null) {
-          const terminal = main.content;
-          terminal.session.send({
-            type: 'stdin',
-            content: [
-              `cd "${gitModel.pathRepository
-                .split('"')
-                .join('\\"')
-                .split('`')
-                .join('\\`')}"\n`
-            ]
-          });
-        }
-
-        return main;
-      } catch (e) {
-        console.error(e);
-        main.dispose();
-      }
+      return main;

This patch removes the cd <git-repo-path> shell command that causes the issue. To preserve the existing behavior, the cwd argument is set to <git-repo-path> when a terminal session is created via the terminal:create-new JupyterLab command. This preserves the existing application behavior while mitigating the command injection issue.

We have verified that this patch works when applied to a local installation of jupyterlab-git. We have also verified that the cwd argument is available in all versions of JupyterLab 4, so this patch should be fully backwards-compatible.

Workarounds

We recommend that users upgrade to the patched versions listed on this GHSA. However, if a user is unable to upgrade, there are 3 different ways to mitigate this vulnerability without upgrading to a patch.

1. Disable terminals on jupyter-server level:

   c.ServerApp.terminals_enabled =  False
   

2. Disable the terminals server extension:

   jupyter server extension disable jupyter_server_terminals
   

3. Disable the lab extension:

   jupyter labextension disable @jupyterlab/terminal-extension