Impact

This impact users of Shescape on Windows that explicitly configure shell: 'cmd.exe' or shell: true using any of quote/quoteAll/escape/escapeAll.

An attacker may be able to get read-only access to environment variables. Example:

import * as cp from "node:child_process";
import { Shescape } from "shescape";

// 1. Prerequisites
const shescape = new Shescape({
    shell: "cmd.exe",
    // Or
    shell: true, // Only if the default shell is CMD
});

// 2. Payload
const payload = '"%PATH%';

// 3. Usage
let escapedPayload;

escapedPayload = shescape.quote(payload);
// Or
escapedPayload = shescape.quoteAll([payload]);
// Or
escapedPayload = shescape.escape(payload);
// Or
escapedPayload = shescape.escapeAll([payload]);

// And (example)
const result = cp.execSync(`echo Hello ${escapedPayload}`, options);

// 4. Impact
console.log(result.toString());
// Outputs "Hello" followed by the contents of the PATH environment variable

For Shescape prior to v2.0.0, the options object must have shell: 'cmd.exe' or shell: undefined and interpolation: true.

Patches

This bug has been patched in v2.1.2 which you can upgrade to now.

If you are already using v2 of Shescape, no further changes are required. If you are using v1 of Shescape, follow the migration guide to upgrade to v2. There is no plan to release a patch compatible with v1 of Shescape.

Workarounds

Alternatively, users can remove all instances of % from user input before using Shescape.

References

• Shescape Pull Request #1916
• Shescape commit 0a81f1e
• Shescape release v2.1.2

For more information

• Comment on Pull Request #1916
• Comment on commit 0a81f1e
• Open an issue at https://github.com/ericcornelissen/shescape/issues (New issue > Question)