Prototype Pollution in JSON5 via Parse Method

[TheKingTermux]

Description

Dependabot cannot update to the required version as there is already an existing pull request for the latest version
There is already an existing pull request for the latest version: 2.2.3

Prototype Pollution in JSON5 via Parse Method #95
Open Opened 2 minutes ago on json5 (npm) · package-lock.json
Dependabot cannot update to the required version as there is already an existing pull request for the latest version
There is already an existing pull request for the latest version: 2.2.3

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...');
}

Severity Check

• Low
• Moderate
• High
• Critical

Severity Number

7.1 / 10

CVSS base metrics

• Attack vector
  Network

• Attack complexity
  High

• Privileges required
  Low

• User interaction
  None

• Scope
  Unchanged

• Confidentiality
  High

• Integrity
  Low

• Availability
  High

• CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:H

• Weaknesses
  CWE-1321

• CVE ID
  CVE-2022-46175

• GHSA ID
  GHSA-9c47-m6qq-7p4h

Information

Package
json5 (npm)

= 2.0.0, < 2.2.2

References

• GHSA-9c47-m6qq-7p4h

• https://nvd.nist.gov/vuln/detail/CVE-2022-46175

• Should __proto__ property be treated specially? json5/json5#199

• Prototype Pollution in JSON5 json5/json5#295

• Backport fix for CVE-2022-46175 to v1 json5/json5#298