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Es werden Posts vom 2019 angezeigt.

Scanning TLS Server Configurations with Burp Suite

In this post, we present our new Burp Suite extension "TLS-Attacker".
Using this extension penetration testers and security researchers can assess the security of TLS server configurations directly from within Burp Suite.
The extension is based on the TLS-Attacker framework and the TLS-Scanner, both of which are developed by the Chair for Network and Data Security.

You can find the latest release of our extension at: https://github.com/RUB-NDS/TLS-Attacker-BurpExtension/releases

Why Receipt Notifications increase Security in Signal

This blog post is aimed to express and explain my surprise about Signal being more secure than I thought (due to receipt acknowledgments). I hope you find it interesting, too.

Signal, and especially its state update protocol, the Double Ratchet algorithm, are widely known for significantly increasing security for instant messaging. While most users first see the end-to-end security induced by employing Signal in messaging apps, the properties achieved due to ratcheting go far beyond protecting communication against (active) attackers on the wire. Due to updating the local device secrets via the Double Ratchet algorithm, the protocol ensures that attackers, who temporarily obtain a device's local storage (on which Signal runs), only compromise confidentiality of parts of the communications with this device. Thus, the leakage of local secrets from a device only affects security of a short frame of communication. The exact duration of compromise depends on the messaging pattern among…

Scanning for Padding Oracles

As you might have heard, we recently got our paper on padding oracle attacks accepted to the USENIX Security Conference. In this paper, we describe and evaluate a scanning methodology with which we found several padding oracle vulnerabilities in devices from various vendors. In total, we found that 1.83% of the Alexa Top 1 Million have padding oracle vulnerabilities.

To test whether a server is vulnerable, we specified different padding oracle vectors which we send to the system under test, using different cipher suites and protocol versions. If the server does not behave identically (on both the TLS and TCP layers), we consider it to be vulnerable to a padding oracle attack, since it is leaking information about the plaintext via behavior differences. Depending on the responses to such padding oracle vectors, one can estimate which implementation is responsible for the vulnerability. We contacted quite a few website owners and tried to cooperate with them, to find out which vendors …

Playing with TLS-Attacker

In the last two years, we changed the TLS-Attacker Project quite a lot but kept silent about most changes we implemented. Since we do not have so much time to keep up with the documentation (we are researchers and not developers in the end), we thought about creating a small series on some of our recent changes to the project on this blog.




We hope this gives you an idea on how to use the most recent version (TLS-Attacker 2.8). If you feel like you found a bug, don't hesitate to contact me via GitHub/Mail/Twitter. This post assumes that you have some idea what this is all about. If you have no idea, checkout the original paper from Juraj or our project on GitHub.

TLDR: TLS-Attacker is a framework which allows you to send arbitrary protocol flows.

Quickstart:
# Install & Use Java JDK 8
$ sudo apt-get install maven
$ git clone https://github.com/RUB-NDS/TLS-Attacker
$ cd TLS-Attacker
$ mvn clean package

So, what changed since the release of the original paper in 2016? Quite a lot! We …

How To Spoof PDF Signatures

One year ago, we received a contract as a PDF file. It was digitally signed. We looked at the document - ignoring the "certificate is not trusted" warning shown by the viewer - and asked ourselfs:

"How do PDF signatures exactly work?"

We are quite familiar with the security of message formats like XML and JSON. But nobody had an idea, how PDFs really work. So we started our research journey.

Today, we are happy to announce our results. In this blog post, we give an overview how PDF signatures work and on top, we reveal three novel attack classes for spoofing a digitally signed PDF document. We present our evaluation of 22 different PDF viewers and show 21 of them to be vulnerable. We additionally evaluated 8 online validation services and found 6 to be vulnerable.

In cooperation with the BSI-CERT, we contacted all vendors, provided proof-of-concept exploits, and helped them to fix the issues and three generic CVEs for each attack class were issued: CVE-2018-16042