Subverting Stateful Firewalls with Protocol States

Amit Klein*

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

1 Scopus citations


We analyzed the generation of protocol header fields in the implementations of multiple TCP/IP network stacks and found new ways to leak information about global protocol states. We then demonstrated new covert channels by remotely observing and modifying the system's global state via these protocol fields. Unlike earlier works, our research focuses on hosts that reside in firewalled networks (including source address validation - SAV), which is a very common scenario nowadays. Our attacks are designed to be non-disruptive - in the exfiltration scenario, this makes the attacks stealthier and thus extends their longevity, and in case of host alias resolution and similar techniques - this ensures the techniques are ethical. We focused on ICMP, which is commonly served by firewalls, and on UDP, which is forecasted to take a more prominent share of the Internet traffic with the advent of HTTP/3 and QUIC, though we report results for TCP as well. The information leakage scenarios we discovered enable the construction of practical covert channels which directly pierce firewalls, or indirectly establish communication via hosts in firewalled networks that also employ SAV. We describe and test three novel attacks in this context: exfiltration via the firewall itself, exfiltration via a DMZ host, and exfiltration via co-resident containers. These are three generic, new use cases for covert channels that work around firewalling and enable devices that are not allowed direct communication with the Internet, to still exfiltrate data out of the network. In other words, we exfiltrate data from isolated networks to the Internet. We also explain how to mount known attacks such as host alias resolution, de-NATting and container co-residence detection, using the new information leakage techniques.

Original languageAmerican English
Title of host publication29th Annual Network and Distributed System Security Symposium, NDSS 2022
PublisherThe Internet Society
ISBN (Electronic)1891562746, 9781891562747
StatePublished - 2022
Externally publishedYes
Event29th Annual Network and Distributed System Security Symposium, NDSS 2022 - Hybrid, San Diego, United States
Duration: 24 Apr 202228 Apr 2022

Publication series

Name29th Annual Network and Distributed System Security Symposium, NDSS 2022


Conference29th Annual Network and Distributed System Security Symposium, NDSS 2022
Country/TerritoryUnited States
CityHybrid, San Diego

Bibliographical note

Publisher Copyright:
© 2022 29th Annual Network and Distributed System Security Symposium, NDSS 2022. All Rights Reserved.


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