Fixed DNS UDP port in totd DNS forwarder (CVE-2022-34294)

["Philipp Jeitner (SIT)" <philipp.jeitner () sit fraunhofer de>]

We hereby disclose the discovery of a DNS Cache poisoning vulnerability 
in totd DNS forwarder. totd is a non-caching DNS forwarder/proxy which 
has not been further developed for a long time, yet it is still used in 
some residential router firmwares. Because the projects age, there are 
no patches available for the described issues.

Our findings are published in our 2022 paper "XDRI Attacks - and - How 
to Enhance Resilience of Residential Routers" in August 2022.

Discovery/Credits
-----------------

Philipp Jeitner, Lucas Teichmann and Haya Shulman
Fraunhofer SIT

References
----------

    - totd: https://github.com/fwdillema/totd
    - paper website: https://xdi-attack.net/
    - paper presentation: 
https://www.usenix.org/conference/usenixsecurity22/presentation/jeitner



CVE-2022-34294: Fixed UDP port in DNS queries sent to upstream resolvers
-------------------------------------------------------------------------

totd uses a fixed UDP source port in upstream queries sent to DNS 
resolvers which allows DNS cache poisoning as there is not enough 
entropy to prevent traffic injection attacks.

## Summary

The router/forwarder uses a fixed UDP port for all queries sent to 
upstream resolvers.

## Impact

Attackers who control a script or web-site which is loaded on a client 
of the vulnerable router/forwarder can exploit this to poison the DNS 
cache by classic DNS poisoning attacks with spoofed IP address of the 
upstream resolver.

## Steps to reproduce

Connect a computer to the vulnerable router/forwarder and trigger 
multiple DNS queries. Observe the queries sent to upstream resolvers via 
packet capture, either on the routers Internet-facing interface or the 
upstream resolver's network interface. The queries captured on these 
interfaces have the same UDP source port (port 1024 in our tests).

## Detailed description and publication timeline

This attack is known to be practical since the 2008 publication "Black 
Ops 2008: It’s The End Of The Cache As We Know It" 
(https://www.blackhat.com/presentations/bh-jp-08/bh-jp-08-Kaminsky/BlackHat-Japan-08-Kaminsky-DNS08-BlackOps.pdf). 
During an evaluation of DNS vulnerabilities in routers, we found this 
attack to be still applicable.