Impact
This only impacts users that use the escape or escapeAll functions with the interpolation option set to true. Example:
import cp from "node:child_process";
import * as shescape from "shescape";
// 1. Prerequisites
const options = {
shell: "bash",
// Or
shell: "dash",
// Or
shell: "powershell.exe",
// Or
shell: "zsh",
// Or
shell: undefined, // Only if the default shell is one of the affected shells.
};
// 2. Attack (one of multiple)
const payload = "foo #bar";
// 3. Usage
let escapedPayload;
shescape.escape(payload, { interpolation: true });
// Or
shescape.escapeAll(payload, { interpolation: true });
cp.execSync(`echo Hello ${escapedPayload}!`, options);
// _Output depends on the shell being used_
The result is that if an attacker is able to include whitespace in their input they can:
- Invoke shell-specific behaviour through shell-specific special characters inserted directly after whitespace.
- Affected shells: Bash, Dash, Zsh, PowerShell
- Invoke shell-specific behaviour through shell-specific special characters inserted or appearing after line terminating characters.
- Invoke arbitrary commands by inserting a line feed character.
- Affected Shells: Bash, Dash, Zsh, PowerShell
- Invoke arbitrary commands by inserting a carriage return character.
- Affected Shells: PowerShell
Patches
Behaviour number 1 has been patched in v1.5.7 which you can upgrade to now. No further changes are required.
Behaviour number 2, 3, and 4 have been patched in v1.5.8 which you can upgrade to now. No further changes are required.
Workarounds
The best workaround is to avoid having to use the interpolation: true option - in most cases using an alternative is possible, see the recipes for recommendations.
Alternatively, you can strip all whitespace from user input. Note that this is error prone, for example: for PowerShell this requires stripping '\u0085' which is not included in JavaScript's definition of \s for Regular Expressions.
References
For more information
NVD description
Shescape is a simple shell escape package for JavaScript. Affected versions were found to have insufficient escaping of white space when interpolating output. This issue only impacts users that use the `escape` or `escapeAll` functions with the `interpolation` option set to `true`. The result is that if an attacker is able to include whitespace in their input they can: 1. Invoke shell-specific behaviour through shell-specific special characters inserted directly after whitespace. 2. Invoke shell-specific behaviour through shell-specific special characters inserted or appearing after line terminating characters. 3. Invoke arbitrary commands by inserting a line feed character. 4. Invoke arbitrary commands by inserting a carriage return character. Behaviour number 1 has been patched in [v1.5.7] which you can upgrade to now. No further changes are required. Behaviour number 2, 3, and 4 have been patched in [v1.5.8] which you can upgrade to now. No further changes are required. The best workaround is to avoid having to use the `interpolation: true` option - in most cases using an alternative is possible, see [the recipes](https://github.com/ericcornelissen/shescape#recipes) for recommendations. Alternatively, users may strip all whitespace from user input. Note that this is error prone, for example: for PowerShell this requires stripping `'\u0085'` which is not included in JavaScript's definition of `\s` for Regular Expressions.