Expert discloses details of 3 Tor zero-day flaws … new ones to come

Pierluigi Paganini July 30, 2020

A security researcher published the details about two Tor zero-day vulnerabilities and plans to release three more flaws.

The security researcher Dr. Neal Krawetz has published technical details about two Tor zero-day vulnerabilities over the past week and promises to release three more. Oppressive regimes could exploit these Tor zero-day flaws to prevent users from accessing the popular anonymizing network.

The expert confirmed that one of these three new issues can de-anonymize Tor servers revealing their real IP address.

Dr. Neal Krawetz decided to publicly disclose details on two zero-day flaws after the Tor Project has repeatedly failed to fix multiple vulnerabilities he reported over the past years.

The researcher also promised to reveal at least three more Tor zero-days, including one that can reveal the real-world IP address of Tor servers.

The researcher operates multiple Tor nodes, last week he published a blog post that describes how internet service providers and organizations could stop Tor connections.

“However, what if there was a distinct packet signature provided by every Tor node that can be used to detect a Tor network connection? Then you could set the filter to look for the signature and stop all Tor connections. As it turns out, this packet signature is not theoretical.” reads the post.

An attacker could use the packet signature to block Tor connections from initiating.

Today the expert published a new blog post that provides details about other Tor zero-day issues that could be exploited by attackers to detect indirect connections,

“Direct connections to the Tor network are the most common type of connection. However, there are also indirect ways to connect to the Tor network. These indirect methods are called ‘bridges’. If someone could detect every bridge protocol, then every Tor user could be blocked from accessing the Tor network, or they can be directly surveilled. (If they know your real network address, then they know who you are, and they can monitor or censor your activities.)” reads the report.

“In this blog entry, I’m going to disclose methods to identify Tor bridge network traffic. This includes two new zero-day (0day) exploits — one for detecting obfs4 and one for detecting meek.”

Tor bridges (“Tor bridge relays”) are alternative entry points to the Tor network, some of them are not listed publicly. Using a bridge makes it harder, but not impossible, for the ISP to determine a user is connecting to Tor.

According to Dr. Krawetz, an attacker can easily detect connections to Tor bridges tracking specific packets.

“Between my previous blog entry and this one, you now have everything you need to enforce the policy with a real-time stateful packet inspection system. You can stop all of your users from connecting to the Tor network, whether they connect directly or use a bridge,” continues Dr. Krawetz.

The security researcher reported multiple issues to the Tor Project, but he claims that the maintainers have never addressed them, for this reason, Dr. Krawetz decided to interrupt its collaboration with the organization.

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Pierluigi Paganini

(SecurityAffairs – hacking, Tor zero-day flaw)

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