mattcg / starttls Goto Github PK

Would be great if this did not warn against using with Node 4.x, seems to work fine.

With node, when making a tls connection, the authorized status and authorizationError includes the result of the certificate idenity check, see https://github.com/nodejs/node/blob/master/lib/_tls_wrap.js#L1091.

With starttls, the identicy check is done after, https://github.com/mattcg/starttls/blob/master/lib/starttls.js#L96, and is done unconditionally, so that if a cert is not trusted, but does pass the tls.checkServerIdentity() check, someone using your example code will consider the connection valid, even though .authorized may be false.

From the README:

  starttls(options, function(err) {
        if (err) {

does not appear secure to me under these conditions.

Also,

starttls(socket, function(err) {
    if (!tls.checkServerIdentity(host, this.cleartext.getPeerCertificate())) {

        // Hostname mismatch!
        // Report error and end connection...
    }
});

this appears to completely ignore the error object, so a naive use of it will accept invalid certs, that purport to be for the hostname the user is trying to make a secure connection to but have not been validly issued by a trusted CA.

Currently starttls doesn't verify the hostname.
This enables a MITM attack because it is enough to present just any signed certificate.

A workaround is to check in the secure handler (in addition to pair.cleartext.authorized) with:

var cert = pair.cleartext.getPeerCertificate()
if(!tls.checkServerIdentity(hostname, cert)) {
  // hostname mismatch
}

It might be a good idea to move this check into the starttls lib itself.
That would require some api changes, as currently starttls doesn't even know the hostname.

Also checkServerIdentity is not officially documented which might become an issue with future node releases.

Because of these two issues (possibly breaking the api and undocumented function) I'd like to get some feedback first before starting to create a patch + pull request. ;-)

In the meantime it is probably best to at least document this in the example code.