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Comment by tptacek | Hacker News Reader

This is an interesting post from Cloudflare, as usual, but it's not clear to me why they would have been vulnerable to CopyFail. Did I miss the point in this blog where that's addressed? What triggered the threat hunting and mitigation exploit? At what points in their architecture were they reliant on Linux user-based access control?

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They weren't vulnerable to it in anything but an academic sense. They call that out up front: "There was no impact to the Cloudflare environment, no customer data was at risk, and no services were disrupted at any point."

This was probably written by their security team. Security teams are paranoid. They want everything patched everywhere all at once at a severity level zeo. Also, PR. Also, also, if through some lack of imagination, this was somehow involved in an exploit of their services, it would look really really bad. So, CYA.

Yeah I think what I'm trying to clarify here is: are they doing a threat hunting exercise out of concern for multitenant exposures, or out of concern for internal privilege escalation?

Cross-tenant would be very surprising! But I don't know enough about their architecture.

It's weird, right? The underlying CNE primitive here, for CopyFail, is not novel. These happen all the time. Why the announcement? Is it just because CopyFail got so much attention?

I can upload arbitrary code to Cloudflare workers, which they run on their systems. It's sandboxed, but in the big bad Internet, if you were Cloudflare, how much would you really trust that sandbox?

It's not running with direct access to Linux kernel system calls, is it?

Let's say an attacker escapes the sandbox and gets a local non-root shell on the machine. At that point, how much more access does escaping to root gain the attacker? (This is a rhetorical question. Cloudflare doesn't say, which I think is the point of this line of questioning.)

Not actually knowing anything about their architecture, but if you somehow gained root on a Cloudflare worker box, the system that I'm sure they've design against this attack for, is for that attacker to then be able to steal the private keys for all the TLS traffic hitting that machine, and then exfiltrate all data going through it and also inject their own content to visitors.

Why are you sure of that? I wouldn't design a critical system that relied on the difference between root and non-root accounts to protect private keys. I would design a system assuming the attacker can trivially escalate to root privilege. Because historically you just cannot rely on the difference. LPE attacks simply happen on too regular a basis.

I'm not sure of anything. I agree that priv escalation regularly happens, I was around for cve-2010-4258, before they got all branded and named. GP was asking why Cloudflare should be so afraid that they wrote that post and I'm saying their fear is reasonable.

https://blog.nelhage.com/2010/12/cve-2010-4258-from-dos-to-p...

The whole IT industry is reliant on Linux user-based access controls, it is not a Cloudflare thing.

Also leaving a massive gap like this behind would be a mistake on multiple levels. For example, it might get combined with another exploit that can achieve unprivileged access to some piece of metal, or you can have a disgruntled employee without admin access escalating their permissions on a box they aren't supposed to see all the secrets.

> For example, it might get combined with another exploit that can achieve unprivileged access ...

Yeah. TFA mentions datacenters in 330 cities. That's a lot of Linux boxen. And many of those have, by definition, ports opened to the big bad Internet. These Linux servers are running services. They answer to ping, for a start. I even heard some are running DNS servers. Remote local exploits are a thing.

What does CloudFlare prefer: that when the next remote local exploit surface all their fleet is one copy.fail away from privilege escalation to root or that they get the time (seen that they obviously have quite advanced detection measures in place) to detect the intruder before it gains root everywhere?

It's Linux. It's datacenters in 330 cities. Linux powers the world and that's how things works.

I, for one, I'm glad to own CloudFlare stocks since right after the 2022 crash and, for two, I'm happy they don't let their huge fleet of Linux servers with a non-patched exploit.

I'm not asking why they'd need to go threat-hunting if there was an ICMP kernel RCE in Linux. CopyFail requires someone untrusted running shell commands somewhere. Where is that exposure in their architecture?

I'm asking because I don't think they have such an exposure.

At the very least, Cloudflare hosts web workers, which let a customer execute more-or-less arbitrary wasm code on their servers. If there's an exploit that lets you escape the wasm sandbox, copy.fail can be chained into (afaiu) an exploit against the Linux host. That's a pretty big risk.

Also, Cloudflare hosts some AI services, so it's possible that some consumers are running Python code in their containers, without the wasm sandbox.

If there's a direct link from Cloudflare workers / WASM to uid=nobody execve or arbitrary syscalls on their hosts, they're already fucked, so I don't think that's true.

I don't understand your point.

You seem so pressed on the fact "why would they even patch this!!!", maybe because its best practice to patch things? You never known what things could be chained together, so you might as well patch this, given its so obviously bad.

That's a straw man and not what he asked. Literally, he asked: "why they would have been vulnerable to CopyFail?"

I've been a sysadmin/programmer since the mid-90s. Local root exploits are a dime a dozen. If your infrastructure relies upon the tenuous difference between root and non-root accounts, you've already lost. Cloudflare isn't an ISP handing out shell accounts on Unix machines.

So again, yes, of course you should patch your Linux machines. Defense in depth and all that. But the question remains: "why Cloudflare would have been vulnerable to CopyFail?" (in anything but an academic sense). Because I do not believe that they can possibly be relying on the difference between root and non-root account.

I don't care about your credentials. It doesn't take a genius to realize that having known major security holes is not ideal.

It is pretty clear they aren't too concerned about this being a issue for this business, after the first paragraph in bold on the blog:

"There was no impact to the Cloudflare environment, no customer data was at risk, and no services were disrupted at any point. Read on to learn how our preparedness paid off."

As mentioned, you never want to give options to a potential attacker/exploit by keeping known vulnerabilities present in your system. You cannot always predict every single avenue an attack could leverage.

Imagine having a data center with barbed wire fences, guard posts, security and cameras covering every square meter of the facility. You wouldn't just leave a door right open because in theory, people shouldn't be able to walk right in. But why would you willingly leave a door open? Even if the possibility is 0.000001%?

People like you would be the first to turn and say "Cloudflare are morons for not patching this!!! Me and my 1 billion years experience and goat status would of prevented this' when some major Cloudflare hack occurs and it was found that phishing 30 different people and using 9 different exploits (including Copyfail) allowed the attacker to bring down Cloudfare

I mean, in some sense, Cloudflare simply accepts the security posture of "already lost", right? They run workloads for multiple users within the same process separated by nothing more than V8 boundaries, which even Chrome (which always claimed to run tabs in separate processes but actually didn't due to various edge cases) finally stopped doing (now afaik they do fence origins within processes) as it was so risky... Cloudflare's best lines of defense past "we patch often" are merely that they sort of KYC at least most of their users so they can log everything they run with their identity and that they take users of similar trust levels (age of account, level of KYC, amount of usage, etc.) and group those into processes... but, at the end of the day, they rely on something that I would certainly never consider reasonable to ship in production.

> They run workloads for multiple users within the same process

Ah, then the root/non-root distinction means even less. They don't even distinguish between non-root accounts! Again, I'm not arguing against them defensively patching their systems against known exploits—they'd be crazy not to; just agreeing with Thomas that they can't be relying upon protecting root from non-root accounts as part a normal operational security boundary.

To wit: if an attacker escapes V8, it's unclear that leveraging "Copy Fail" to escape from non-root to root buys the attacker a whole lot more.

I would assume it was about protecting their servers from internal sources escalating privileges vs. them providing publicly accessible Linux shells.

I mean, that's a real project, but Linux LPEs kind of grow on trees, so you can't literally rely on threat intelligence for this problem; presumably you handle it by drastically scoping down and surveilling what people do on prod hosts.

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