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Be careful. New platforms invite bad actors. (infosec.pub)
submitted 1 year ago* (last edited 1 year ago) by Rooster@infosec.pub to c/technology@beehaw.org
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Found the error Not allowed to load local resource: file:///etc/passwd while looking at infosec.pub's communities page. There's a community called "ignore me" that adds a few image tags trying to steal your passwd file.

You have to be extremely poorly configured for this to work, but the red flags you see should keep you on your toes for the red flags you don't.

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[-] Rooster@infosec.pub 17 points 1 year ago

If you find something, report it. Don't experiment on the public.

https://www.bugcrowd.com/resources/guide/what-is-responsible-disclosure/

[-] drwho@beehaw.org 1 points 1 year ago

My first thought was that a Javascript library pulled from a CDN got spiked.

[-] flashgnash@lemm.ee 0 points 1 year ago

That harmless self retweeting tweet was pretty funny though

[-] himazawa@infosec.pub 10 points 1 year ago* (last edited 1 year ago)

Is this, by any chance, originated from the sub called ignore me? In that case is probably my bad because is set as the image of the channel. I was playing with lemmy in the previous version and forgot about it, sorry.

I created that channel to investigate why the lemmy instance was hanging every time there was a symbol in the URL, added that URI as icon for fun and forgot about it.

That alert appears because your browser is trying to load an image with that path, nothing dangerous or remotely exploitable, don't worry.

Edit: I removed it so you shouldn't see the alert anymore.

P.S. no, it's not trying to steal anything, it's your browser trying to load that file as an image but instead of being let's say this url: https://beehaw.org/pictrs/image/c0e83ceb-b7e5-41b4-9b76-bfd152dd8d00.png (this sub icon) , it's this one file:///etc/passwd so you browser is doing the request to your own file. Don't worry, nothing got compromised.

/cc @shellsharks@infosec.pub

[-] BlueBockser@programming.dev 0 points 1 year ago

But... why? Why even put that URL there? Even if it was most likely harmless for all users, this still looks like an attempt at data exfiltration.

[-] himazawa@infosec.pub 1 points 1 year ago

Because I wanted to try if others URI schemas were supported instead of http / https. file:// was a valid one. Don't worry, the day an attempt of data exfil will happen, you will not see it though your console logs.

[-] jcg@halubilo.social 1 points 1 year ago

I doubt this person ever expected anyone to find it or to read that much into it lol

[-] farthom@lemmy.ca 8 points 1 year ago

Holy shit this is kind of unsettling. Though I would expect ALL major browsers to reject reading any local files like this..... would this kind of thing actually succeed somewhere/somehow?

[-] Rooster@infosec.pub 6 points 1 year ago

If you ran your browser as root and configured your browser to load local resources on non-local domains maybe. I think you can do that in chrome://flags but you have to explicitly list the domains allowed to do it.

I'm hoping this is just a bad joke.

[-] skullgiver@popplesburger.hilciferous.nl 1 points 1 year ago* (last edited 11 months ago)

[This comment has been deleted by an automated system]

[-] fox@vlemmy.net 1 points 1 year ago

you don't need to be root to read /etc/passwd

[-] trachemys@iusearchlinux.fyi 4 points 1 year ago

That’s because passwd doesn’t store the password hashes. Just user names.

[-] Greg@lemmy.ca 3 points 1 year ago* (last edited 1 year ago)

Are you sure? What do you get when you run $ cat /etc/passwd in terminal? Just paste the results here 😇

Edit: to anyone reading this on the future, don't actually do this, it was a joke

[-] fox@vlemmy.net 6 points 1 year ago

yup pretty sure

$ cat /etc/passwd
fox:hunter2:1000:1000::/home/fox:/usr/bin/zsh

😉

[-] animist@lemmy.one 5 points 1 year ago

Weird, all I see is *******

[-] delial@lemmy.sdf.org 1 points 1 year ago* (last edited 1 year ago)

Since you told me not to. There isn't a risk on most linux systems; passwords were moved to /etc/shadow a long time ago. It only leaks the names of your users and largely useless info for most attackers:

root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/usr/sbin/nologin
man:x:6:12:man:/var/cache/man:/usr/sbin/nologin
lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin
mail:x:8:8:mail:/var/mail:/usr/sbin/nologin
news:x:9:9:news:/var/spool/news:/usr/sbin/nologin
uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin
proxy:x:13:13:proxy:/bin:/usr/sbin/nologin
www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin
backup:x:34:34:backup:/var/backups:/usr/sbin/nologin
list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin
irc:x:39:39:ircd:/run/ircd:/usr/sbin/nologin
gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin
nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin
_apt:x:100:65534::/nonexistent:/usr/sbin/nologin
systemd-network:x:101:102:systemd Network Management,,,:/run/systemd:/usr/sbin/nologin
systemd-resolve:x:102:103:systemd Resolver,,,:/run/systemd:/usr/sbin/nologin
messagebus:x:999:999:System Message Bus:/:/usr/sbin/nologin
systemd-timesync:x:998:998:systemd Time Synchronization:/:/usr/sbin/nologin
systemd-coredump:x:997:997:systemd Core Dumper:/:/usr/sbin/nologin
delial:x:1000:1000:,,,:/home/delial:/bin/bash
sshd:x:103:65534::/run/sshd:/usr/sbin/nologin
xrdp:x:104:110::/run/xrdp:/usr/sbin/nologin
dictd:x:105:111:Dictd Server,,,:/var/lib/dictd:/usr/sbin/nologin
nm-openvpn:x:106:112:NetworkManager OpenVPN,,,:/var/lib/openvpn/chroot:/usr/sbin/nologin
sssd:x:107:113:SSSD system user,,,:/var/lib/sss:/usr/sbin/nologin
[-] marvin@lemmy.sdf.org 1 points 1 year ago

Well it's not completely useless. It offers some insights into the system. Which service accounts exists, what usernames are used.

If an attacker finds a valid username they can then start bruteforcing the password.

From your account list we can see you have sshd and xrdp. Do they both provide the same kind of bruteforce protection? Are there any recent exploits for either?

[-] delial@lemmy.sdf.org 1 points 1 year ago

That's why I said largely useless. An attacker can narrow down the attack surface by ignoring anything that can't login, but that just leaves them with root and delial, and they already knew or could've guessed both of those pieces of information (in this context anyway).

And as you noted when looking at the service accounts, they might be able to login or crack their way in via xrdp or sshd. So, unless you're port-forwarding those protocols from the internet, how useful is that really? I would say largely useless. Assuming they port-scanned your public IP, they still need either an insecure config or an unpatched, remotely exploitable bug.

That being said, you're totally right. The average Linux user isn't "administering" their system, so they probably aren't following their distribution's security mailing list, installing security patches as they're released, and actually RTFM. It's best for the average user to play it unbelievably safe.

In this case, the machine isn't actually running xrdp, and sshd doesn't accept passwords or root logins. (Although, I need to setup knockd to protect that non-standard sshd port a bit more.) All passwords used on the system are random and longer than 32 characters. My router doesn't port-forward to this machine, either.

This has been an exercise of Cunningham's Law for the benefit of those reading.

[-] farthom@lemmy.ca 0 points 1 year ago

Yeah, seems highly unlikely to ever yield any results. Even if you did manage to read a file, you have to get lucky finding a password hash in a rainbow table or the password being shit enough to crack.

[-] nzodd@beehaw.org 0 points 1 year ago

Also generally the actual password (or rather its hash) is stored in /etc/shadow on most systems from the past 20 odd years.

[-] lemmyvore@feddit.nl 1 points 1 year ago

And if anybody has publicly accessible ssh on their desktop machine, that allows password login, they're kinda asking for it.

[-] dotslashme@infosec.pub 6 points 1 year ago* (last edited 1 year ago)

Can confirm it's still there for the ignore me community.

[-] Penguincoder@beehaw.org 1 points 1 year ago

Nice share, thanks for the information. Definitely need to be careful both as a server operator with Lemmy, and a user of it.

[-] laenurd@lemmy.lemist.de 0 points 1 year ago

While this is concerning, I wonder what the author(s) of this were thinking would happen. I assume it's supposed to be an attempt at stealing the server's passwords, since I at least know of no browser that freely allows access to local files.

[-] ollien@beehaw.org 2 points 1 year ago

FWIW, /etc/passwd itself contains no passwords (the name exists for historical reasons) but it definitely is a globally accessible file that can give you clues about the target system. Given this, it's more likely the user is attempting to find out if arbitrary disk reads are possible by using a well known path on many servers.

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this post was submitted on 29 Jun 2023
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