NodeJS/express/3.0.0-alpha3

Express ressource injection

A vulnerability has been identified in the Express response.links function, allowing for arbitrary resource injection in the Link header when unsanitized data is used.

The issue arises from improper sanitization in Link header values, which can allow a combination of characters like ,, ;, and <> to preload malicious resources.

This vulnerability is especially relevant for dynamic parameters.

No Charset in Content-Type Header in express

Vulnerable versions of express do not specify a charset field in the content-type header while displaying 400 level response messages. The lack of enforcing user's browser to set correct charset, could be leveraged by an attacker to perform a cross-site scripting attack, using non-standard encodings, like UTF-7.

Recommendation

For express 3.x, update express to version 3.11 or later. For express 4.x, update express to version 4.5 or later.

qs vulnerable to Prototype Pollution

qs before 6.10.3, as used in Express before 4.17.3 and other products, allows attackers to cause a Node process hang for an Express application because an __ proto__ key can be used. In many typical Express use cases, an unauthenticated remote attacker can place the attack payload in the query string of the URL that is used to visit the application, such as a[proto]=b&a[proto]&a[length]=100000000. The fix was backported to qs 6.9.7, 6.8.3, 6.7.3, 6.6.1, 6.5.3, 6.4.1, 6.3.3, and 6.2.4 (and therefore Express 4.17.3, which has deps: qs@6.9.7 in its release description, is not vulnerable).

express improperly controls modification of query properties

Impact

when using the extended query parser in express ('query parser': 'extended'), the request.query object inherits all object prototype properties, but these properties can be overwritten by query string parameter keys that match the property names

[!IMPORTANT]
the extended query parser is the default in express 4; this was changed in express 5 which by default uses the simple query parser

Patches

the issue has been patched to ensure request.query is a plain object so request.query no longer has object prototype properties. this brings the default behavior of extended query parsing in line with express's default simple query parser

Workaround

this only impacts users using extended query parsing ('query parser': 'extended'), which is the default in express 4, but not express 5. all users are encouraged to upgrade to the patched versions, but can otherwise work around this issue:

provide qs directly and specify plainObjects: true

app.set('query parser',
  function (str) {
    return qs.parse(str, {
      plainObjects: true
  });
});

express vulnerable to XSS via response.redirect()

Impact

In express <4.20.0, passing untrusted user input - even after sanitizing it - to response.redirect() may execute untrusted code

Patches

this issue is patched in express 4.20.0

Workarounds

users are encouraged to upgrade to the patched version of express, but otherwise can workaround this issue by making sure any untrusted inputs are safe, ideally by validating them against an explicit allowlist

Details

successful exploitation of this vector requires the following:

1. The attacker MUST control the input to response.redirect()
2. express MUST NOT redirect before the template appears
3. the browser MUST NOT complete redirection before:
4. the user MUST click on the link in the template

Express.js Open Redirect in malformed URLs

Impact

Versions of Express.js prior to 4.19.2 and pre-release alpha and beta versions before 5.0.0-beta.3 are affected by an open redirect vulnerability using malformed URLs.

When a user of Express performs a redirect using a user-provided URL Express performs an encode using encodeurl on the contents before passing it to the location header. This can cause malformed URLs to be evaluated in unexpected ways by common redirect allow list implementations in Express applications, leading to an Open Redirect via bypass of a properly implemented allow list.

The main method impacted is res.location() but this is also called from within res.redirect().

Patches

https://github.com/expressjs/express/commit/0867302ddbde0e9463d0564fea5861feb708c2dd https://github.com/expressjs/express/commit/0b746953c4bd8e377123527db11f9cd866e39f94

An initial fix went out with express@4.19.0, we then patched a feature regression in 4.19.1 and added improved handling for the bypass in 4.19.2.

Workarounds

The fix for this involves pre-parsing the url string with either require('node:url').parse or new URL. These are steps you can take on your own before passing the user input string to res.location or res.redirect.

References

https://github.com/expressjs/express/pull/5539 https://github.com/koajs/koa/issues/1800 https://expressjs.com/en/4x/api.html#res.location

No Charset in Content-Type Header

Vulnerable versions of express do not specify a charset field in the content-type header while displaying 400 level response messages. The lack of enforcing user's browser to set correct charset, could be leveraged by an attacker to perform a cross-site scripting attack, using non-standard encodings, like UTF-7.