Version Details and Security Vulnerabilities

Impact

Using Babel to compile code that was specifically crafted by an attacker can lead to arbitrary code execution during compilation, when using plugins that rely on the path.evaluate()or path.evaluateTruthy() internal Babel methods.

Known affected plugins are:

• @babel/plugin-transform-runtime
• @babel/preset-env when using its useBuiltIns option
• Any "polyfill provider" plugin that depends on @babel/helper-define-polyfill-provider, such as babel-plugin-polyfill-corejs3, babel-plugin-polyfill-corejs2, babel-plugin-polyfill-es-shims, babel-plugin-polyfill-regenerator

No other plugins under the @babel/ namespace are impacted, but third-party plugins might be.

Users that only compile trusted code are not impacted.

Patches

The vulnerability has been fixed in @babel/traverse@7.23.2.

Babel 6 does not receive security fixes anymore (see Babel's security policy), hence there is no patch planned for babel-traverse@6.

Workarounds

• Upgrade @babel/traverse to v7.23.2 or higher. You can do this by deleting it from your package manager's lockfile and re-installing the dependencies. @babel/core >=7.23.2 will automatically pull in a non-vulnerable version.
• If you cannot upgrade @babel/traverse and are using one of the affected packages mentioned above, upgrade them to their latest version to avoid triggering the vulnerable code path in affected @babel/traverse versions:
  • @babel/plugin-transform-runtime v7.23.2
  • @babel/preset-env v7.23.2
  • @babel/helper-define-polyfill-provider v0.4.3
  • babel-plugin-polyfill-corejs2 v0.4.6
  • babel-plugin-polyfill-corejs3 v0.8.5
  • babel-plugin-polyfill-es-shims v0.10.0
  • babel-plugin-polyfill-regenerator v0.5.3

The parse method of the JSON5 library before and including version 2.2.1 does not restrict parsing of keys named __proto__, allowing specially crafted strings to pollute the prototype of the resulting object.

This vulnerability pollutes the prototype of the object returned by JSON5.parse and not the global Object prototype, which is the commonly understood definition of Prototype Pollution. However, polluting the prototype of a single object can have significant security impact for an application if the object is later used in trusted operations.

Impact

This vulnerability could allow an attacker to set arbitrary and unexpected keys on the object returned from JSON5.parse. The actual impact will depend on how applications utilize the returned object and how they filter unwanted keys, but could include denial of service, cross-site scripting, elevation of privilege, and in extreme cases, remote code execution.

Mitigation

This vulnerability is patched in json5 v2.2.2 and later. A patch has also been backported for json5 v1 in versions v1.0.2 and later.

Details

Suppose a developer wants to allow users and admins to perform some risky operation, but they want to restrict what non-admins can do. To accomplish this, they accept a JSON blob from the user, parse it using JSON5.parse, confirm that the provided data does not set some sensitive keys, and then performs the risky operation using the validated data:

const JSON5 = require('json5');

const doSomethingDangerous = (props) => {
  if (props.isAdmin) {
    console.log('Doing dangerous thing as admin.');
  } else {
    console.log('Doing dangerous thing as user.');
  }
};

const secCheckKeysSet = (obj, searchKeys) => {
  let searchKeyFound = false;
  Object.keys(obj).forEach((key) => {
    if (searchKeys.indexOf(key) > -1) {
      searchKeyFound = true;
    }
  });
  return searchKeyFound;
};

const props = JSON5.parse('{"foo": "bar"}');
if (!secCheckKeysSet(props, ['isAdmin', 'isMod'])) {
  doSomethingDangerous(props); // "Doing dangerous thing as user."
} else {
  throw new Error('Forbidden...');
}

If the user attempts to set the isAdmin key, their request will be rejected:

const props = JSON5.parse('{"foo": "bar", "isAdmin": true}');
if (!secCheckKeysSet(props, ['isAdmin', 'isMod'])) {
  doSomethingDangerous(props);
} else {
  throw new Error('Forbidden...'); // Error: Forbidden...
}

However, users can instead set the __proto__ key to {"isAdmin": true}. JSON5 will parse this key and will set the isAdmin key on the prototype of the returned object, allowing the user to bypass the security check and run their request as an admin:

const props = JSON5.parse('{"foo": "bar", "__proto__": {"isAdmin": true}}');
if (!secCheckKeysSet(props, ['isAdmin', 'isMod'])) {
  doSomethingDangerous(props); // "Doing dangerous thing as admin."
} else {
  throw new Error('Forbidden...');
}

The NPM package micromatch prior to version 4.0.8 is vulnerable to Regular Expression Denial of Service (ReDoS). The vulnerability occurs in micromatch.braces() in index.js because the pattern .* will greedily match anything. By passing a malicious payload, the pattern matching will keep backtracking to the input while it doesn't find the closing bracket. As the input size increases, the consumption time will also increase until it causes the application to hang or slow down. There was a merged fix but further testing shows the issue persisted prior to https://github.com/micromatch/micromatch/pull/266. This issue should be mitigated by using a safe pattern that won't start backtracking the regular expression due to greedy matching.

A vulnerability was found in Braces versions prior to 2.3.1. Affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) attacks.

Versions of braces prior to 2.3.1 are vulnerable to Regular Expression Denial of Service (ReDoS). Untrusted input may cause catastrophic backtracking while matching regular expressions. This can cause the application to be unresponsive leading to Denial of Service.

Recommendation

Upgrade to version 2.3.1 or higher.

The NPM package braces fails to limit the number of characters it can handle, which could lead to Memory Exhaustion. In lib/parse.js, if a malicious user sends "imbalanced braces" as input, the parsing will enter a loop, which will cause the program to start allocating heap memory without freeing it at any moment of the loop. Eventually, the JavaScript heap limit is reached, and the program will crash.