The big news this week was that OpenSSH has an unauthorized Remote Code Execution exploit. Or more precisely, it had one that was fixed in 2006, that was unintentionally re-introduced in version 8.5p1 from 2021. The flaw is a signal handler race condition, where async-unsafe code gets called from within the SIGALARM handler. What does that mean?
Continue reading “This Week In Security: Hide Yo SSH, Polyfill, And Packing It Up”
Researchers at Eset have published a huge report on the Ebury malware/botnet (pdf), and one of the high profile targets of this campaign was part of the kernel.org infrastructure. So on one hand, this isn’t new news, as the initial infection happened back in 2011, and was reported then. On the other hand, according to the new Eset report, four kernel.org servers were infected, with two of them possibly compromised for as long as two years. That compromise apparently included credential stealing or password cracking.
The Ebury attackers seem to gain initial access through credential stuffing — a huge list of previously captured credentials are tried one at a time. However, once the malware has a foothold in the network, a combination of automated and manual steps are taken to move laterally. The most obvious is to grab any private SSH keys from that system, and try using them to access other machines on the local network. Ebury also replaces a system library that gets called as a part of sshd, libkeyutils.so. This puts it in a position to quietly capture credentials.
For a targeted attack against a more important target, the people behind Ebury seem to go hands-on-keyboard, using techniques like Man-in-the-Middle attacks against SSH logins on the local network using ARP spoofing. In this case, someone was doing something nasty.
And that doesn’t even start to cover the actual payload. That’s nasty too, hooking into Apache to sniff for usernames and passwords in HTTP/S traffic, redirecting links to malicious sites, and more. And of course, the boring things you might expect, like sending spam, mining for Bitcoin, etc. Ebury isn’t exactly easy to notice, either, since it includes a rootkit module that hooks into system functions to hide itself. Thankfully there are a couple of ways to get a clean shell to look for the malware, like using systemd-run or launching a local shell on the system console.
And the multi-million dollar question: Who was behind this? Sadly we don’t know. A single arrest was made in 2014, and recovered files implicated another Russian citizen, but the latest work indicates this was yet another stolen identity. The rest of the actors behind Ebury have gone to great lengths to remain behind the curtain.
Continue reading “This Week In Security: The Time Kernel.org Was Backdoored And Other Stories”
The xz backdoor is naturally still the top story of the week. If you need a refresher, see our previous coverage. As expected, some very talented reverse engineers have gone to work on the code, and we have a much better idea of what the injected payload does.
One of the first findings to note is that the backdoor doesn’t allow a user to log in over SSH. Instead, when an SSH request is signed with the right authentication key, one of the certificate fields is decoded and executed via a system() call. And this makes perfect sense. An SSH login leaves an audit trail, while this backdoor is obviously intended to be silent and secret.
It’s interesting to note that this code made use of both autotools macros, and the GNU ifunc, or Indirect FUNCtions. That’s the nifty feature where a binary can include different versions of a function, each optimized for a different processor instruction set. The right version of the function gets called at runtime. Or in this case, the malicious version of that function gets hooked in to execution by a malicious library. Continue reading “This Week In Security: XZ, ATT, And Letters Of Marque”
In breaking news that dropped just after our weekly security column went live, a backdoor has been discovered in the xz package, that could potentially compromise SSH logins on Linux systems. The most detailed analysis so far seems to be by [Andres Freund] on the oss-security list.
The xz release tarballs from 5.6.0 in late February and 5.6.1 on March 9th both contain malicious code. A pair of compressed files in the repository contain the majority of the malicious patch, disguised as test files. In practice, this means that looking at the repository doesn’t reveal anything amiss, but downloading the release tarballs gives you the compromised code.
This was discovered because SSH logins on a Debian sid were taking longer, with more CPU cycles than expected. And interestingly, Valgrind was throwing unexpected errors when running on the liblzma library. That last bit was first discovered on February 24th, immediately after the 5.6.0 release. The xz-utils package failed its tests on Gentoo builds.
Continue reading “Security Alert: Potential SSH Backdoor Via Liblzma”
Android, the popular mobile phone OS, is essentially just Linux with a nice user interface layer covering it all up. In theory, it should be able to do anything a normal computer running Linux could do. And, since most web servers in the world are running Linux, [PelleMannen] figured his Android phone could run a web server just as well as any other Linux machine and built this webpage that’s currently running on a smartphone, with an additional Reddit post for a little more discussion.
The phone uses Termux (which we’ve written about briefly before) to get to a Bash shell on the Android system. Before that happens, though, some setup needs to take place largely involving installing F-Droid through which Termux can be installed. From there the standard SSH and Apache servers can be installed as if the phone were running a normal Linux The rest of the installation involves tricking the phone into thinking it’s a full-fledged computer including a number of considerations to keep the phone from halting execution when the screen locks and other phone-specific issues.
With everything up and running, [PelleMannen] reports that it runs surprisingly well with the small ARM system outputting almost no heat. Since the project page is being hosted on this phone we can’t guarantee that the link above works, though, and it might get a few too many requests to stay online. We wish it were a little easier to get our pocket-sized computers to behave in similar ways to our regular laptops and PCs (even if they don’t have quite the same amount of power) but if you’re dead-set on repurposing an old phone we’ve also seen them used to great effect in place of a Raspberry Pi.
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.
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”
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”
