Shescape vulnerable to insufficient escaping of whitespace
### Impact
This only impacts users that use the `escape` or `escapeAll` functions with the `interpolation` option set to `true`. Example:
```javascript
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:
1. Invoke shell-specific behaviour through shell-specific special characters inserted directly after whitespace.
- Affected shells: _Bash_, _Dash_, _Zsh_, _PowerShell_
2. Invoke shell-specific behaviour through shell-specific special characters inserted or appearing after line terminating characters.
- Affected shells: _Bash_
3. Invoke arbitrary commands by inserting a line feed character.
- Affected Shells: _Bash_, _Dash_, _Zsh_, _PowerShell_
3. 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
https://github.com/ericcornelissen/shescape#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
-
https://github.com/ericcornelissen/shescape/pull/322
-
https://github.com/ericcornelissen/shescape/pull/324
-
https://github.com/ericcornelissen/shescape/pull/332
-
https://github.com/ericcornelissen/shescape/releases/tag/v1.5.7
-
https://github.com/ericcornelissen/shescape/releases/tag/v1.5.8
### For more information
- Comment on:
- For behaviour 1 (PowerShell):
https://github.com/ericcornelissen/shescape/pull/322
- For behaviour 1 (Bash, Dash, Zsh):
https://github.com/ericcornelissen/shescape/pull/324
- For behaviour 2, 3, 4 (_any shell_):
https://github.com/ericcornelissen/shescape/pull/332
- Open an issue at
https://github.com/ericcornelissen/shescape/issues (_New issue_ > _Question_ > _Get started_)
- If you're missing CMD from this advisory, see
https://github.com/ericcornelissen/shescape/security/advisories/GHSA-jjc5-fp7p-6f8w
[v1.5.7]:
https://github.com/ericcornelissen/shescape/releases/tag/v1.5.7
[v1.5.8]:
https://github.com/ericcornelissen/shescape/releases/tag/v1.5.8