Shescape: Home-directory disclosure in assignment context on Unix with Dash

Impact

This impacts users of Shescape on Unix systems that explicitly configure shell to Dash, or true when the default shell is Dash, using the escape and escapeAll APIs in assignments prefixed to a command.

An attacker may be able to obtain the location of the home directory and, depending on how it is used, change the location on which a command operates in unexpected ways.

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

// 1. Prerequisites
const options = {
    shell: "dash",
    // Or
    shell: true, // Only if the default shell is Dash
};

// 2. Payload
const payload = ":~";

// 3. Usage
const shescape = new Shescape(options);
let escapedPayload;

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

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

// 4. Impact
console.log(result.toString());
// Outputs ":" followed by the user's home directory

Patches

This bug has been patched in [v2.1.14] and [v3.0.1] which you can upgrade to now.

If you are already using v3 of Shescape, no further changes are required. If you are using v2 of Shescape it is recommended to upgrade as this version reaches end-of-life status on 2026-09-28, follow the [migration guide] to upgrade to v3.

No patches will be released for version of Shescape lower than v2.0.0.

Workarounds

Alternatively, users of Shescape can 1) refrain from using Dash, 2) use the env option of the node:child_process API to inject variables with untrusted values instead, or 3) remove all instances of ~ from untrusted inputs.

For more information

• Comment on Pull Request [#2651] for v2 and [#2649] for v3
• Comment on commit [b4b34c3] for v2 and [43d70b5] for v3
• Open an issue at https://github.com/ericcornelissen/shescape/issues (New issue > Question)