Impact
If no TLS configuration is provided by the user, the websocket package constructs its own TLS configuration using recommended defaults. When looking up a WSS endpoint using the DNS TXT record method described in XEP-0156: Discovering Alternative XMPP Connection Methods the ServerName field was incorrectly being set to the name of the server returned by the TXT record request, not the name of the initial server we were attempting to connect to. This means that any attacker that can spoof a DNS record (ie. in the absence of DNSSEC, DNS-over-TLS, DNS-over-HTTPS, or similar technologies) could redirect the user to a server of their choosing and as long as it had a valid TLS certificate for itself the connection would succeed, resulting in a MITM situation.
Patches
All users should upgrade to v0.21.1.
Workarounds
To work around the issue, manually specify a TLS configuration with the correct hostname.
References
For more information
If you have any questions or comments about this advisory:
moparisthebest Analyst
Impact
If no TLS configuration is provided by the user, the websocket package constructs its own TLS configuration using recommended defaults. When looking up a WSS endpoint using the DNS TXT record method described in XEP-0156: Discovering Alternative XMPP Connection Methods the ServerName field was incorrectly being set to the name of the server returned by the TXT record request, not the name of the initial server we were attempting to connect to. This means that any attacker that can spoof a DNS record (ie. in the absence of DNSSEC, DNS-over-TLS, DNS-over-HTTPS, or similar technologies) could redirect the user to a server of their choosing and as long as it had a valid TLS certificate for itself the connection would succeed, resulting in a MITM situation.
Patches
All users should upgrade to v0.21.1.
Workarounds
To work around the issue, manually specify a TLS configuration with the correct hostname.
References
For more information
If you have any questions or comments about this advisory: