Flipping Pages: New Linux vulnerability in nf_tables and exploitation techniques

https://github.com/Notselwyn/CVE-2024-1086/blob/main/src/mai...

Linked page says

> The exploit affects versions from (including) v5.14 to (including) v6.6, excluding patched branches v5.15.149>, v6.1.76>, v6.6.15>.

?

Quick question: for "post"-exploitation, once you had a KSMA-like primitive why would you choose to still do the modprobe_path dance, and introduce a pid bruteforce for fileless :(, instead of e.g. patching kernel .text with a short shellcode to become root & break out of namespaces?

> netfilter: nf_tables: accept QUEUE/DROP verdict parameters

> Allow userspace to specify the queue number or the errno code for QUEUE and DROP verdicts.

In a strange twist of fate, the original author was Patrick McHardy who is now a persona non grata. Unless Pablo can remember or dig it from his emails, it probably won't ever be clear exactly what the use case was, at least not through basic investigation.

But also e.g. by the chrome sandbox used by e.g. electron apps (or e.g. 1password). Through that sandbox helper binary can also work with being a suid program.

I also wouldn't be too surprised if e.g. proton will start using user namspaces at some point in the future.

So for any non-hardened desktop linux system you probably should _not_ disable it!

(For many servers or special hardened Linux it often isn't a bad idea to disable it.)

the problem is that containers require tons of hacks on the network side to just-work. and docker main selling point is all the usafe hacks it does for it.

so obviously, any container solution will adopt these hacks eventually, and there is the problem.

you end up with a perfectly sane namespace functionality that removes access, but then the kernel opens the gate because network hacks are good

For example, Chrome uses namespaces to implement its process sandbox. However, Chrome installs a setuid-root binary, so that it doesn't need "unpriveleged" namespaces enabled. This is sad, though: setuid-root binaries are inherently a security risk of their own. It would be nice if Chrome did not need to install a suid-root binary. But, it can only possibly avoid this in the future if unprivileged user namespaces are widely available. Bugs like this unfortunately delay that future.

Incidentally, programs like Chrome that set up namespace-based sandbox also commonly use seccomp to prevent the sandboxed code from using exotic kernel features -- including namespaces. So user namespaces won't be available to sandboxed code regardless of whether you enable unprivileged user namespaces at the system level.

Personally I feel that on a single-user desktop, there's little point in enforcing a separation between users and root -- everything interesting is probably available to your user account anyway. But sandboxes like Chrome's are obviously essential to security on desktops. So I'd tend to say, on a single-user desktop, enabling unprivileged user namespaces improves security overall, by encouraging the use of sandboxes.

Multi-user systems are a different story, obviously.

https://lwn.net/Articles/882397/

https://bugs.launchpad.net/bugs/cve/2024-1086

> A use-after-free vulnerability in the Linux kernel's netfilter: nf_tables component can be exploited to achieve local privilege escalation. The nft_verdict_init() function allows positive values as drop error within the hook verdict, and hence the nf_hook_slow() function can cause a double free vulnerability when NF_DROP is issued with a drop error which resembles NF_ACCEPT. We recommend upgrading past commit f342de4e2f33e0e39165d8639387aa6c19dff660.

longer answer: It is definitely really damn hard these days. Even disabling the mitigations, it's still pretty hard to find and a vuln and write an exploit. But many people who find these (not all though) work as part of a team, where they can parallelize fuzzing efforts and combine/chain knowledge and other exploits much better than an individual could. The level of expertise and talent that some of these people have is absolutely incredible, and experience is worth a pound of gold for these types of things, and some people have years or decades of experience.

there are "classic" techniques to bypass most of the modern protections and if there isn't then researchers often come up with novel attacks / bypasses. for example for heap protections you can see how2heap to bypass heap protections[0]. another example is an exploit which allows bypass of KASLR (which has since been patched)[1]. it looks like this exploit comes up with a "dirty pagetable" technique[2].

it's always a game of cat and mouse with more mitigations always being added while researchers constantly look to bypass them.

[0] https://github.com/shellphish/how2heap

[1] https://www.willsroot.io/2022/12/entrybleed.html

[2] https://pwning.tech/nftables/#452-the-technique

Just think of the gap between the first time in the woodworking shop and a carpenter, first time pottery versus a master, a new painter and a professional artist. Think of how many things the master can do that it is literally impossible for the new person to do. Then add another 10-100x as much time on that. That is the gap.

[1] https://zerodium.com/program.html

But when you consider that major bugs found now are being found by well funded teams or state actors trying to exploit them, it makes more sense that they would be able to work around existing mitigations due to the sheer manpower and resources they have to throw at the problem.

https://daniel.haxx.se/blog/2024/01/02/the-i-in-llm-stands-f...

git clone https://github.com/Notselwyn/CVE-2024-1086

cd CVE-2024-1086

/disable your wifi (the author says it's increasing chances of the exploit working)/

./exploit

If it runs till the end, then you should update your kernel

There's a super long list there, but most everything has been updated or superceded.

The standard (updated) kernels are:

  * Focal: 5.4.0-174.193
  * Jammy: 5.15.0-101.111
  * Mantic: 6.5.0-26.26

> The exploit does not work v6.4> kernels with kconfig CONFIG_INIT_ON_ALLOC_DEFAULT_ON=y (including Ubuntu v6.5)

> The exploits requires user namespaces (kconfig CONFIG_USER_NS=y), that those user namespaces are unprivileged (sh command sysctl kernel.unprivileged_userns_clone = 1), and that nf_tables is enabled (kconfig CONFIG_NF_TABLES=y). By default, these are all enabled on Debian, Ubuntu, and KernelCTF. Other distro's have not been tested, but may work as well.

Also with other distros like Fedora and Arch, the kernel versions change frequently including new big versions (like 6.4 to 6.5, what in semver would be called "minor" but isn't super accurate for the linux kernel) so that list would be outdated very quickly if not immediately (for example my Fedora machine right now is on kernel 6.7.9, way beyond what is vulnerable). It's quite possible that Ubuntu is the only vulnerable distro given the way they manage kernel versions. That's not a criticism of Ubuntu, because there are pros and cons of each approach, but in this case it does probably make Ubuntu more vulnerable. RHEL and derivatives also tend to stick on a version long term, and it looks like RHEL 9.3 is on kernel 5.14 so could be vulnerable but it's at the very beginning of the range. That would be a useful thing to know.

I think it's also (generally) far more useful for most people to hear a descriptor that most closely aligns with something they can readily identify whether it affects them or not. Then people can look at the details themselves.

Edit: added a little more on other distros like Fedora and Arch