Microsoft leaks TLS private key for cloud ERP product
… and it was still in use for more than 100 days after the initial report
At my old job, I was working as a software developer customizing the Microsoft ERP product Dynamics 365 for Finance and Operations (formerly known as Dynamics AX). To provide some context: ERP stands for Enterprise Resource Planning and is software which supports all critical core business processes of a company like purchasing, manufacturing, product planning, sales, finance and many others by integrating those into one application with a single database.
Last year Microsoft started to offer it’s ERP product as a web-based cloud-hosted SaaS solution. The software is hosted in Azure managed by Microsoft. It’s accessible through a comprehensive control panel (Life Cycle Services) which empowers the user to manage every single aspect of the environment, like the deployment of changes to the software or applying updates.
One quite useful feature is direct RDP access to the machine running the software to debug issues with the application. A normal deployment is divided into at least three systems: development, user acceptance testing (also referred to as “sandbox”) and production. The user acceptance system mirrors the setup of the production environment with a single exception: while there’s no way to access the production servers besides through the web interface, the sandbox environment offers administrative RDP access. And that’s where the fun begins ;-)
After a long workday while being off the clock I accessed a sandbox environment via RDP to take a look and learn how Microsoft would set up a server hosting such a business critical application. The hostname for a sandbox environment is customername.sandbox.operations.dynamics.com. A quick glance at the certificates inside the built-in “Certificate Manager” revealed something shocking:
Sitting there in plain sight was a valid TLS certificate for the common name *.sandbox.operations.dynamics.com and the corresponding private key — by the courtesy of Microsoft IT SSL SHA2 CA! This certificate is shared across all sandbox environments, even those hosted for other Microsoft customers. It’s used to encrypt the web traffic between the users of the software and the server. All you need to extract this certificate is access to ANY sandbox environment.
I still could not believe my eyes, so clearly the next goal was to export the private key to make sure it’s actually possible to export it and use it outside the system. In Windows, the private keys are marked as non-exportable by default and the Certificate Manager refuses to export those. A short C++ program hooking the internal certificate API functions called to check whether a certificate is exportable and a couple minutes later, I had the private key in my hands.
The implications of this are far-reaching: an attacker, which has the ability to listen and/or interject himself between the connection from the user to the server (man in the middle), can impersonate the server and thus read all communication in clear text. Furthermore, an attacker can modify the communication and thus insert malicious content. Since the attacker can use the original TLS certificate, there’s no warning or error on the client side. Just the green padlock indicating a secure connection. The users of this user acceptance (sandbox) systems are high-value targets. They are usually in key positions at the respective organization and have access to valuable information. The sandbox system itself often also contains sensitive information to make the tests more realistic. There is even a feature to copy the production database into the sandbox environment to enable this use case.
This left me with the question, whether the production environment was affected. A quick look at the certificate served by a production system accessible at customername.operations.dynamics.com revealed, that it was indeed a wildcard certificate (*.operations.dynamics.com). Since the production system has no direct RDP access, it’s not possible to simply extract the certificate as described above. One possible attack vector was the capability to deploy customization (.NET assemblies, .sql scripts, configuration files etc.) onto a production system which enables an attacker to execute code in the production environment. Because there’s no way anybody would let me deploy this on a customer live production environment and there’s no chance to acquire one of those environments for simple testing (licensing issues and associated cost, special agreements), my research had to stop there. While the ability to execute code on a target system in my opinion usually increases the likelihood of exploitation, considering all the known facts I’m not in a position to determine if production systems were affected or not. A Microsoft spokesperson later commented that “[c]ontrols exist in production environments that render the described technique ineffective [..]”.
Another theoretically feasible attack vector is to redirect the victim to an production environment controlled by the attacker using some man-in-the-middle attach technique. Since both environments used the same certificate and the attacker has control over his system, he could get the user to enter sensitive information into his own environment.
With the TLS private key in hand, it was time to contact the Microsoft Security Response Center (MSRC) via PGP-encrypted mail (firstname.lastname@example.org). While I couldn’t believe that the TLS certificate was exposed like this, the communication with Microsoft was even more disturbing:
I’ve sent this initial successful message on 08/17/17:
I’ve noticed a vulnerability in the Microsoft managed Azure hosted Dynamics 365 for Operations environments.
Each separate customer environment (called AOS in the Dynamics world — Windows Server 2012 R2 — IIS, accessible by MS customers via RDP) uses the same wildcard server certificate (including the private key) for the domain *.sandbox.operations.dynamics.com, meaning the service hosted for Acme Inc. at acme.sandbox.operations.dynamics.com uses the same TLS wildcard certificate as Evil Inc. hosted at evil.sandbox.operations.dynamics.com.
Reproduction steps / possible attack scenario:
— Bob working as CFO at ACME Inc, Environment hosted at acme.sandbox.operations.dynamics.com
— Attacker Eve trying to steal ACMEs trade secrets working at the competitor Evil Inc, Environment hosted at evil.sandbox.operations.dynamics.com
1. Attacker Eve visits lcs.dynamics.com and acceses the Azure VM hosting the environment of Evil Inc using the provided RDP file and Administrator credentials — this is the intended way to access your own environment.
2. Attacker Eve uses the tool “mimikatz” on this VM to export the public and private key pair of the wildcard certificate for *.sandbox.operations.dynamics.com — Eve has rightfully full administrative access on the hosted azure environment so this is no issue
3. Attacker Eve uses this certificate for a man in the middle attack against Bob and poses as acme.sandbox.dynamics.com
4. Bob access the acme.sandbox.operations.dynamics.com environment, the traffic gets MITMd by Eve. The attacker has full access to the data being transmitted. Since Dynamics 365 for Operations is an ERP System, it’s a high value target. Bob doesn’t see any difference, since the certificate in use is a legitimate one.
During the creation of the environment issue an individual certificate unique for each customer environment.
I haven’t checked the production environment because of legal and ethical reasons, however visiting acme.operations.dynamics.com also is being served with a wild card certificate issued for *.operations.dynamics.com. Since Eve could deploy code to the production environment, it should be possible to extract this certificate, too.
Please let me know if i can be of any assistance. Furthermore, please keep me updated about the status.
Later I’ve sent a follow-up email containing an encrypted copy of the previously extracted private key.
Having not received a initial response informing me that somebody at Microsoft received my report, three days later I’ve sent a follow-up mail asking for confirmation, that they got my report. Five days after my initial report I receive this answer:
Thank you for following up on this thread. From how I am interpreting this report, it sounds as though the attacker has already received or bypassed admin credentials. As such, this typically would not meet the bar for security servicing.
Can you provide a scenario where the attacker does not have, or did not bypass, admin credentials — or, a case where the admin credentials were somehow stolen?
I’ve replied with a more detailed explanation of the problem, but until today never got any response to this email thread. Anticipating that I would never get any answer on this thread (which proved to be true) I tried to reach out to an individual working at the PKI Operations team inside Microsoft, which manages the public CA and compliance work. I’ve sent out my mail detailing the problem on 08/23/17 in hope that PKI Operations could reach out to MSRC and make them aware of this issue. On the same day, I’ve got a very friendly response notifying me that he’s reaching out to MSRC. A day later I get this response:
Wanted to update you that I’ve been chatting with a senior manager in MSRC. He isn’t able to find your case based on the number you gave below. Any chance you have the actual case number?
I did not yet receive a case number from the MSRC team, all I had until now was only the CRM ticket number in the subject line. Did I maybe make a mistake while copy-pasting the CRM ticket number in the previous mail? To make sure it’s the correct number I forwarded the reply I’ve got from the MSRC team (see above) with the ticket number in the subject line to the individual at PKI Operations. He informed me, that the MSRC team could not find my mail. So we agreed that I would send a new mail to the MSRC mailbox (email@example.com) from a different mail address.
This time around I actually got a case number a few hours later:
Thank you very much for your report.
I have opened case 40397 and the case manager, Sean will be in touch when there is more information.
If at any time you have questions or want to share more information, please respond to this message.
Microsoft Security Response Center
With the new case number, I’ve contacted the very helpful individual at PKI Operations and two days later got this response:
Update, the folks at MSRC still aren’t able to find this case, but the manager involved a bunch more people, so we are all looking into this 😊
A day later the individual at PKI Operations informed me that MSRC has found the mail and is actively engaged. I’m very thankful for the effort put in by the individual to get my report in front of the right people, though in an ideal world this step should not have been necessary.
Since I still haven’t heard from MSRC a week later, I’ve continued to follow-up on a weekly basis.
To be clear: I did not expect resolution of the problem within a couple of weeks, all I wanted was a simple response like “Yep, we’ve got your mail and a human is looking into it” directly from the MSRC team.
There are so many stories online like this one, where the ticket did not get any attention for years. Since Dynamics 365 for Finance and Operations is business critical software and the data transferred over the TLS connection is of very sensitive nature I wanted to make sure that somebody is actually working on this problem.
At the end of September after various follow-up mails, I still have not received a single response from MSRC on both threads. So I’ve sent them an mail detailing that this would be my last attempt to contact them and a full disclosure would trigger, if they would not respond within the next 10 days.
Ten days later having received no response from MSRC, out of desperation and curiosity I’ve tried to contact the regular Microsoft support using their online chat feature in hope they could get me in touch with someone in the organisation or at least forward a message to them. I’ve detailed what happened until now and explained, that I’m trying to reach the MSRC team. A few minutes later, I’ve received this phone number from the support: (562) 981–7600. Could that be the real deal? A call to this number revealed, that it belongs to the Marine Spill Response Corporation (MSRC), the largest, dedicated oil spill and emergency response organization in the United States. I’m sure a leaked TLS certificate is a serious offense, but is a different kind of leak which needs a different kind of expertise to be handled ;-)
In a last-ditch effort, I even tried to reach out to them via twitter.
I’ve almost given up at this point in time, but to my surprise, I received a response on twitter followed by a mail a couple of days later ensuring me that “the servicing team for this endpoint [is] expressly committed to fixing this issue as soon as possible. I will keep you posted with updates.”
At this point, it should be clear to the reader, that neither of those things happened. The certificate was still out there in use — more than 100 days after the initial discovery. Follow-ups remained unanswered.
Frustrated with the experience, I started to write this blog post with the intent to do a “Full Disclosure”, but then decided against it due to the nature of the affected systems. Instead, I’ve decided to contact journalists at German IT news outlets via PGP encrypted mail.
Hanno Böck, a freelance journalist writing for many German outlets including Golem.de responded to my inquiry and as a result of our communication directly engaged with Microsoft’s public relations office and opened a ticket on the Mozilla bug tracker.
The “Baseline Requirements Certificate Policy”, a policy document stating all requirements which have to be met in order for a certificate issuing entity to be included into the trust store of most browsers, issued by the “CA/Browser Forum” states that “the CA SHALL revoke a Certificate within 24 hours […]”. As a web browser vendor Mozilla does a good job at making sure those policies are being followed, which was the reason for opening a ticket with them.
Not even a week later a new case manager at MSRC finally replied to my ticket that all wildcard certificates associated with Dynamics 365 for Finance and Operations have been revoked and replaced with customer-environment-specific ones.
You can find the story published by Hanno Böck @ Golem here (now in English as well): https://www.golem.de/news/microsoft-dynamics-365-wildcard-certificate-with-a-private-key-for-everyone-1712-131544.html
While the specific security issue is now resolved, this experience showed me once more that there are many unresolved problems of systemic nature in the way the integrity of computing systems and digital communication is ensured. But that’s a topic for another blog post.
You can reach out to me via twitter (@cerebuild) or e-mail at firstname.lastname@example.org. You can find the legal notice required by German law on most websites here.
08/14/17 — Initial discovery of the leaked certificate
08/17/17 — First successful contact to MSRC (thread #1)
08/22/17 — Response from MSRC, detailing that it doesn’t meet the bar for security servicing (thread #1). Last mail from MSRC on this thread.
08/22/17 — Mail sent to MSRC detailing why this issue should be dealt with (thread #1)
08/23/17 — First mail to individual at PKI Operations
08/23/17 — Response from PKI Operations
08/24/17 — Response from PKI Operations that MSRC is not able to find my case
08/24/17 — Forwarded MSRC mail (thread #1) to PKI Operations
08/25/17 — Response from PKI Operations that MSRC is still trying to find the mail
08/25/17 — Offered to re-send the mail to MSRC using a different mail address to PKI Operations
08/25/17 — Sent problem description to MSRC again (thread #2)
08/25/17 — Received a reply from MSRC with a case number (thread #2). This was the last mail received from MSRC on this thread.
08/26/17 — Forwarded mail with the case number to PKI Operations
08/28/17 — Received mail from PKI Operations detailing that MSRC was still looking for the new case (thread #2)
08/29/17 — Received mail from PKI Operations that MSRC found the mail.
09/01/17 — Received mail from individual at PKI Operations that he’s dropping off this, because MSRC is “actively engaged”
09/07/17 — Follow-up with MSRC (thread #2) — No response
09/12/17 — Follow-up with MSRC (thread #2) — No response
09/18/17 — Follow-up with MSRC (thread #2) — No response
09/26/17 — Follow-up with MSRC (thread #2) — No response
10/04/17 — Tweet to @msftsecresponse
10/10/17 — Finally got the first response via Twitter + mail
11/15/17 — Last follow-up
11/29/17 — Ticket on Mozilla’s Bug Tracker and second line of communication with Microsoft has been opened by the journalist Hanno Böck
12/05/17 — Issue has been fixed by Microsoft, got reply from MSRC