Hanno's blog

tl;dr Dell laptops come preinstalled with a root certificate and a corresponding private key. That completely compromises the security of encrypted HTTPS connections. I've provided an online check, affected users should delete the certificate.

It seems that Dell hasn't learned anything from the Superfish-scandal earlier this year: Laptops from the company come with a preinstalled root certificate that will be accepted by browsers. The private key is also installed on the system and has been published now. Therefore attackers can use Man in the Middle attacks against Dell users to show them manipulated HTTPS webpages or read their encrypted data.

The certificate, which is installed in the system's certificate store under the name "eDellRoot", gets installed by a software called Dell Foundation Services. This software is still available on Dell's webpage. According to the somewhat unclear description from Dell it is used to provide "foundational services facilitating customer serviceability, messaging and support functions".

The private key of this certificate is marked as non-exportable in the Windows certificate store. However this provides no real protection, there are Tools to export such non-exportable certificate keys. A user of the plattform Reddit has posted the Key there.

For users of the affected Laptops this is a severe security risk. Every attacker can use this root certificate to create valid certificates for arbitrary web pages. Even HTTP Public Key Pinning (HPKP) does not protect against such attacks, because browser vendors allow locally installed certificates to override the key pinning protection. This is a compromise in the implementation that allows the operation of so-called TLS interception proxies.

I was made aware of this issue a while ago by Kristof Mattei. We asked Dell for a statement three weeks ago and didn't get any answer.

It is currently unclear which purpose this certificate served. However it seems unliklely that it was placed there deliberately for surveillance purposes. In that case Dell wouldn't have installed the private key on the system.

Affected are only users that use browsers or other applications that use the system's certificate store. Among the common Windows browsers this affects the Internet Explorer, Edge and Chrome. Not affected are Firefox-users, Mozilla's browser has its own certificate store.

Users of Dell laptops can check if they are affected with an online check tool. Affected users should immediately remove the certificate in the Windows certificate manager. The certificate manager can be started by clicking "Start" and typing in "certmgr.msc". The "eDellRoot" certificate can be found under "Trusted Root Certificate Authorities". You also need to remove the file Dell.Foundation.Agent.Plugins.eDell.dll, Dell has now posted an instruction and a removal tool.

This incident is almost identical with the Superfish-incident. Earlier this year it became public that Lenovo had preinstalled a software called Superfish on its Laptops. Superfish intercepts HTTPS-connections to inject ads. It used a root certificate for that and the corresponding private key was part of the software. After that incident several other programs with the same vulnerability were identified, they all used a software module called Komodia. Similar vulnerabilities were found in other software products, for example in Privdog and in the ad blocker Adguard.

This article is mostly a translation of a German article I wrote for Golem.de.

Image source and license: Wistula / Wikimedia Commons, Creative Commons by 3.0

Update (2015-11-24): Second Dell root certificate DSDTestProvider

I just found out that there is a second root certificate installed with some Dell software that causes exactly the same issue. It is named DSDTestProvider and comes with a software called Dell System Detect. Unlike the Dell Foundations Services this one does not need a Dell computer to be installed, therefore it was trivial to extract the certificate and the private key. My online test now checks both certificates. This new certificate is not covered by Dell's removal instructions yet.

Dell has issued an official statement on their blog and in the comment section a user mentioned this DSDTestProvider certificate. After googling what DSD might be I quickly found it. There have been concerns about the security of Dell System Detect before, Malwarebytes has an article about it from April mentioning that it was vulnerable to a remote code execution vulnerability.

Update (2015-11-26): Service tag information disclosure

Another unrelated issue on Dell PCs was discovered in a tool called Dell Foundation Services. It allows webpages to read an unique service tag. There's also an online check.

In February the discovery of a software called Superfish caused widespread attention. Superfish caused a severe security vulnerability by intercepting HTTPS connections with a Man-in-the-Middle-certificate. The certificate and the corresponding private key was shared amongst all installations.

The use of Man-in-the-Middle-proxies for traffic interception is a widespread method, an application installs a root certificate into the browser and later intercepts connections by creating signed certificates for webpages on the fly. It quickly became clear that Superfish was only the tip of the iceberg. The underlying software module Komodia was used in a whole range of applications all suffering from the same bug. Later another software named Privdog was found that also intercepted HTTPS traffic and I published a blog post explaining that it was broken in a different way: It completely failed to do any certificate verification on its connections.

In a later blogpost I analyzed several Antivirus applications that also intercept HTTPS traffic. They were not as broken as Superfish or Privdog, but all of them decreased the security of the TLS encryption in one way or another. The most severe issue was that Kaspersky was at that point still vulnerable to the FREAK bug, more than a month after it was discovered. In a comment to that blogpost I was asked about a software called Adguard. I have to apologize that it took me so long to write this up.

Different certificate, same key

The first thing I did was to install Adguard two times in different VMs and look at the root certificate that got installed into the browser. The fingerprint of the certificates was different. However a closer look revealed something interesting: The RSA modulus was the same. It turned out that Adguard created a new root certificate with a changing serial number for every installation, but it didn't generate a new key. Therefore it is vulnerable to the same attacks as Superfish.

I reported this issue to Adguard. Adguard has fixed this issue, however they still intercept HTTPS traffic.

I learned that Adguard did not always use the same key, instead it chose one out of ten different keys based on the CPU. All ten keys could easily be extracted from a file called ProtocolFilters.dll that was shipped with Adguard. Older versions of Adguard only used one key shared amongst all installations. There also was a very outdated copy of the nss library. It suffers from various vulnerabilities, however it seems they are not exploitable. The library is not used for TLS connections, its only job is to install certificates into the Firefox root store.

Meet Privdog again

The outdated nss version gave me a hint, because I had seen this before: In Privdog. I had spend some time trying to find out if Privdog would be vulnerable to known nss issues (which had the positive side effect that Filippo created proof of concept code for the BERserk vulnerability). What I didn't notice back then was the shared key issue. Privdog also used the same key amongst different installations. So it turns out Privdog was completely broken in two different ways: By sharing the private key amongst installations and by not verifying certificates.

The latest version of Privdog no longer intercepts HTTPS traffic, it works as a browser plugin now. I don't know whether this vulnerability was still present after the initial fix caused by my original blog post.

Now what is this ProtocolFilters.dll? It is a commercial software module that is supposed to be used along with a product called Netfilter SDK. I wondered where else this would be found and if we would have another widely used software module like Komodia.

ProtocolFilters.dll is mentioned a lot in the web, mostly in the context of Potentially Unwanted Applications, also called Crapware. That means software that is either preinstalled or that gets bundled with installers from other software and is often installed without users consent or by tricking the user into clicking some "ok" button without knowing that he or she agrees to install another software. Unfortunately I was unable to get my hands on any other software using it.

Lots of "Potentially Unwanted Applications" use ProtocolFilters.dll

Software names that I found that supposedly include ProtocolFilters.dll: Coupoon, CashReminder, SavingsDownloader, Scorpion Saver, SavingsbullFilter, BRApp, NCupons, Nurjax, Couponarific, delshark, rrsavings, triosir, screentk. If anyone has any of them or any other piece of software bundling ProtocolFilters.dll I'd be interested in receiving a copy.

I'm publishing all Adguard keys and the Privdog key together with example certificates here. I also created a trivial script that can be used to extract keys from ProtocolFilters.dll (or other binary files that include TLS private keys in their binary form). It looks for anything that could be a private key by its initial bytes and then calls OpenSSL to try to decode it. If OpenSSL succeeds it will dump the key.

Finally an announcement for visitors of the Chaos Communication Camp: I will give a talk about TLS interception issues and the whole story of Superfish, Privdog and friends on Sunday.

Update: Due to the storm the talk was delayed. It will happen on Monday at 12:30 in Track South.