Presentation Material

Abstract

Security researchers have done a good amount of practical attacks in the past using chosen plain-text attacks on compressed traffic to steal sensitive data. In spite of how popular CRIME and BREACH were, little was talked about how this class of attacks was relevant to VPN networks. Compression oracle attacks are not limited to TLS protected data. Regardless of the underlying encryption framework being used, these VPN networks offer a very well used feature usually known as TCP Compression which in a way acts almost similar to the TLS compression feature pre-CRIME era.

In this talk, we try these attacks on browser requests and responses which usually tunnel their HTTP traffic through VPNs. We also explore the possibility of attacking ESP Compression and other such optimizations in any tunneled traffic which does encryption. We also show a case study with a well-known VPN server and their plethora of clients.

We then go into practical defenses and how mitigations in HTTP/2’s HPACK and other mitigation techniques are the way forward rather than claiming ‘Thou shall not compress traffic at all.’ One of the things that we would like to showcase is how impedance mismatches in these different layers of technologies affect security and how they don’t play well together.

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The speaker discusses the importance of encryption in VPNs and how compression can be a vulnerability. They mention that some vendors, like OpenVPN have considered disabling compression by default, , while others like WireGuard have already done so. The speaker also shares their experience with a POC (proof-of-concept) attack that leaks secrets across domains, which led to one of the vendors they worked with, in disabling compression.

The speaker emphasizes that VPNs should prioritize encryption at the protocol level, citing examples like TLS and DNS over HTTP. They also suggest that VPN providers should allow users to enable or disable compression for non-secure protocols.

During the Q&A session, an attendee asks if this type of attack would work on other plaintext protocols like FTP, and the speaker responds that it’s possible but hasn’t been explored yet. Another attendee, one of the authors of the BREACH report, asks about HTTP over VPN with no compression but with compressed HTTP traffic on top, and the speaker suggests that it might still be vulnerable to attacks.

Overall, the speaker stresses the importance of prioritizing encryption in VPNs and highlights the need for further research into potential vulnerabilities.