Withdrawn Advisory: express improperly controls modification of query properties

Withdrawn Advisory

This advisory has been withdrawn because it describes a correctness bug, not a vulnerability with real security impact. This link is maintained to preserve external references.

Original Description

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
  });
});