CVE-2023-40185

Shescape on Windows escaping may be bypassed in threaded context

Workarounds

If you are impacted there is no workaround possible.

References

• Shescape Pull Request #1142
• Shescape commit 0b976da
• Shescape release v1.7.4

For more information

• Comment on Pull Request #1142
• Comment on commit 0b976da
• Open an issue at https://github.com/ericcornelissen/shescape/issues (New issue > Question > Get started)

This may impact users that use Shescape on Windows in a threaded context (e.g. using Worker threads). The vulnerability can result in Shescape escaping (or quoting) for the wrong shell, thus allowing attackers to bypass protections depending on the combination of expected and used shell.

This snippet demonstrates a vulnerable use of Shescape:

// vulnerable.js

import { exec } from "node:child_process";
import { Worker, isMainThread } from 'node:worker_threads';

import * as shescape from "shescape";

if (isMainThread) {
  // 1. Something like a worker thread must be used. The reason being that they
  // unexpectedly change environment variable names on Windows.
  new Worker("./vulnerable.js");
} else {
  // 2. Example configuration that's problematic. In this setup example the
  // expected default system shell is CMD. We configure the use of PowerShell.
  // Shescape will fail to look up PowerShell and default to escaping for CMD
  // instead, resulting in the vulnerability.
  const options = {
    shell: "powershell",
    interpolation: true,
  };

  // 3. Using shescape to protect against attacks, this is correct.
  const escaped = shescape.escape("&& ls", options);

  // 4. Invoking a command with the escaped user input, this is vulnerable in
  // this case.
  exec(`echo Hello ${escaped}`, options, (error, stdout) => {
    if (error) {
      console.error(`An error occurred: ${error}`);
    } else {
      console.log(stdout);
    }
  });
}

CVE-2023-40185 has a CVSS score of 8.6 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.7.4); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

This bug has been patched in v1.7.4 which you can upgrade to now. No further changes are required.

1. What is CVE-2023-40185? CVE-2023-40185 is a high-severity security vulnerability in shescape (npm), affecting versions < 1.7.4. It is fixed in 1.7.4.
2. How severe is CVE-2023-40185? CVE-2023-40185 has a CVSS score of 8.6 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of shescape are affected by CVE-2023-40185? shescape (npm) versions < 1.7.4 is affected.
4. Is there a fix for CVE-2023-40185? Yes. CVE-2023-40185 is fixed in 1.7.4. Upgrade to this version or later.
5. Is CVE-2023-40185 exploitable, and should I be worried? Whether CVE-2023-40185 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2023-40185 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2023-40185? Upgrade shescape to 1.7.4 or later.

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