This Week In Security: Bitwarden, Reverse RDP, And Snake

January 5, 2024 by Jonathan Bennett 10 Comments

This week, we finally get the inside scoops on some old stories, starting with the Bitwarden Windows Hello problem from last year. You may remember, Bitwarden has an option to use Windows Hello as a vault unlock option. Unfortunately, the Windows credential API doesn’t actually encrypt credentials in a way that requires an additional Windows Hello verification to unlock. So a derived key gets stored to the credential manager, and can be retrieved through a simple API call. No additional biometrics needed. Even with the Bitwarden vault locked and application closed.

There’s another danger, that doesn’t even require access to the the logged-in machine. On a machine that is joined to a domain, Windows backs up those encryption keys to the Domain Controller. The encrypted vault itself is available on a domain machine over SMB by default. A compromised domain controller could snag a bitwarden vault without ever even running code on the target machine. The good news is that this particular problem with Bitwarden and Windows Hello is now fixed, and has been since version 2023.10.1.

Reverse RDP Exploitation

We normally think about the Remote Desktop Protocol as dangerous to expose to the internet. And it is. Don’t put your RDP service online. But reverse RDP is the idea that it might also be dangerous to connect an RDP client to a malicious server. And of course, multiple RDP implementations have this problem. There’s rdesktop, FreeRDP, and Microsoft’s own mstsc that all have vulnerabilities relating to reverse RDP.

The technical details here aren’t terribly interesting. It’s all variations on the theme of not properly checking remote data from the server, and hence either reading or writing past internal buffers. This results in various forms of information leaks and code executions problems. What’s interesting is the different responses to the findings, and then [Eyal Itkin]’s takeaway about how security researchers should approach vulnerability disclosure.

So first up, Microsoft dismissed a vulnerability as unworthy of servicing. And then proceeded to research it internally, and present it as a novel attack without properly attributing [Eyal] for the original find. rdesktop contained quite a few of these issues, but were able to fix the problem in a handful of months. FreeRDP fixed some issues right away, in what could be described as a whack-a-mole style process, but a patch was cooked up that would actually address the problem at a deeper level: changing an API value from the unsigned size_t to a signed ssize_t. That change took a whopping 2 years to actually make it out to the world in a release. Why so long? Continue reading “This Week In Security: Bitwarden, Reverse RDP, And Snake” →

This Week In Security: Triangulation, ProxyCommand, And Barracuda

December 29, 2023 by Jonathan Bennett 6 Comments

It’s not every day we get to take a good look inside a high-level exploit chain developed by an unnamed APT from the western world. But thanks to some particularly dedicated researchers at Kaspersky, which just happens to be headquartered in Moscow, that’s exactly what we have today. The name Operation Triangulation was picked, based off part of the device fingerprinting code that rendered a yellow triangle on an HTML canvas.

The entire talk is available, given this week at the 37th Chaos Communication Congress, 37c3. The exploit starts with an iMessage attachment, delivered silently, that exploits an undocumented TrueType font instruction. Looking at the source code implies that it was a copy-paste error where a programmer didn’t quite get the logic right for a pointer calculation. That vulnerability gives a memory write primitive that pivots into code execution. What’s particularly interesting is that Apple silently fixed this bug January 2023, and didn’t make any public statements. Presumably there were an uptick of crash logs that pointed to this problem, but didn’t conclusively show attempted exploitation.

The exploits then moves to using NSExpression as a next stage. NSExpression is an ugly way to write code, but it does allow the exploit chain to get to the next stage, running JavaScript as an application, without Just In Time compilation. The JS payload is quite a beast, weighing in at 11,000 lines of obfuscated code. It manages to call native APIs directly from JS, which then sets up a kernel exploit. This is multiple integer overflow flaws that result in essentially arbitrary system memory reads and writes. Continue reading “This Week In Security: Triangulation, ProxyCommand, And Barracuda” →

This Week In Security: Terrapin, Seized Unseized, And Autospill

December 22, 2023 by Jonathan Bennett 5 Comments

There’s a new SSH vulnerability, Terrapin (pdf paper), and it’s got the potential to be nasty — but only in an extremely limited circumstance. To understand the problem, we have to understand what SSH is designed to do. It replaces telnet as a tool to get a command line shell on a remote computer. Telnet send all that text in the clear, but SSH wraps it all inside a public-key encrypted tunnel. It was designed to safely negotiate an unfriendly network, which is why SSH clients are so explicit about accepting new keys, and alerting when a key has changed.

SSH uses a sequence counter to detect Man-in-the-Middle (MitM) shenanigans like packet deletion, replay, or reordering. That sequence isn’t actually included in the packet, but is used as part of the Message Authentication Check (MAC) of several encryption modes. This means that if a packet is removed from the encrypted tunnel, the MAC fails on the rest of the packets, triggering a complete connection reset. This sequence actually starts at zero, with the first unencrypted packet sent after the version banners are exchanged. In theory, this means that an attacker fiddling with packets in the pre-encryption phase will invalidate the entire connection as well. There’s just one problem.

The innovation from the Terrapin researchers is that an attacker with MitM access to the connection can insert a number of benign messages in the pre-encryption phase, and then silently drop the first number of messages in the encrypted phase. Just a little TCP sequence rewriting for any messages between, and neither the server nor client can detect the deception. It’s a really interesting trick — but what can we do with it?

For most SSH implementations, not much. The 9.6 release of OpenSSH addresses the bug, calling it cryptographically novel, but noting that the actual impact is limited to disabling some of the timing obfuscation features added to release 9.5.

Continue reading “This Week In Security: Terrapin, Seized Unseized, And Autospill” →

This Week In Security: Traingate, DNS, And JMP Slides

December 15, 2023 by Jonathan Bennett 5 Comments

Remember Dieselgate, the scandal where certain diesel vehicles would detect an emissions test, and run cleaner for it, “cheating” the test? Traingate may just put that one into perspective. We’ll tell the story from the beginning, but buckle up for a wild and astonishing ride. It all starts with Polish trains getting a maintenance overhaul. These trains were built by Newag, who bid on the maintenance contract, but the contract was won by another company, SPS. This sort of overhaul involves breaking each train into its components, inspecting, lubricating, etc, and putting it all back together again. The first train went through this process, was fully reassembled, and then refused to move. After exhausting all of the conventional troubleshooting measures, SPS brought in the hackers.
Continue reading “This Week In Security: Traingate, DNS, And JMP Slides” →

This Week In Security: LogoFail, National DNS Poison, And DNA

December 8, 2023 by Jonathan Bennett 3 Comments

When there’s a vulnerability in a system library, we install updates, and go on with our lives. When there’s a vulnerability in a Java library, jars get rebuilt, and fixed builds slowly roll out. But what happens when there’s a vulnerability in a library used in firmware builds? And to make it even more fun, it’s not just a single vulnerability. All three major firmware vendors have problems when processing malicious images. And LogoFail isn’t limited to x86, either. UEFI Arm devices are vulnerable, too.
Continue reading “This Week In Security: LogoFail, National DNS Poison, And DNA” →

This Week In Security: Owncloud, NXP, 0-Days, And Fingerprints

December 1, 2023 by Jonathan Bennett 18 Comments

We’re back! And while the column took a week off for Thanksgiving, the security world didn’t. The most pressing news is an issue in Owncloud, that is already under active exploitation.

The problem is a library that can be convinced to call phpinfo() and include the results in the page response. That function reveals a lot of information about the system Owncloud is running on, including environment variables. In something like a Docker deployment, those environment variables may contain system secrets like admin username and password among others.

Now, there is a bit of a wrinkle here. There is a public exploit, and according to research done by Greynoise Labs, that exploit does not actually work against default installs. This seems to describe the active exploitation attempts, but the researcher that originally found the issue has stated that there is a non-public exploit that does work on default installs. Stay tuned for this other shoe to drop, and update your Owncloud installs if you have them. Continue reading “This Week In Security: Owncloud, NXP, 0-Days, And Fingerprints” →

This Week In Security: SSH, FTP, And Reptar

November 17, 2023 by Jonathan Bennett 3 Comments

It’s time to strap on our propeller beanies, because we’re going to talk crypto. The short version is that some SSH handshakes can expose enough information for a third party to obtain the host’s private signing key. That key is the one that confirms you are connecting to the SSH server you think you are, and if the key validation fails, you get a big warning:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!

The math that makes this warning work is public-private key cryptography. The problem we’re talking about today only shows up in RSA authentication. Specifically those that use the Chinese Remainder Theorem (CRT) to quickly calculate the modulos needed to generate the cryptographic signature. If something goes wrong during that calculation, you end up with a signature that is mathematically related to the secret key in a different way than intended. The important point is that knowing this extra value *significantly* weakens the security of the secret key.

This attack has been known for quite some time, but the research has been aimed at causing the calculation fault through power vaults or even memory attacks like Rowhammer. There has also been progress on using a lattice attack against captured handshakes, to make the attack practical with less known information. The real novel element of this week’s approach (pdf) is that it has been tested against SSH.

The paper’s authors performed weekly scans of the entire IPv4 public network space, capturing the handshake from any listening SSH server, and also had 5 years of historic data to draw from. And the results are mixed. There is a Cisco SSH server string that is extremely common in the dataset, and only once did one of these machines send a miscalculated handshake. Possibly a random ram bit flip to blame. And on the other hand, the string “SSH-2.0-Zyxel SSH server” had so many bad signatures, it suggests a device that *always* sends a miscalculated signature. Continue reading “This Week In Security: SSH, FTP, And Reptar” →