A Textbook Buffer Overflow: A Look at the FreeBSD telnetd Code | Hacker News Reader

A Textbook Buffer Overflow: A Look at the FreeBSD telnetd Code

thexploit.com

64 pointsthexploit23 comments

https://twitter.com/#!/cperciva/status/150864360170983424

Ok, but no one uses telnetd, right?

That is probably why it was overlooked

I've seen it being used by oldschool (obsolete) admins. When asked about security they argue the servers are in a DMZ, so it's safe, right?

These days telnet comes wrapped in SSL, so it's totally possible to use it securely. I prefer public keys and almost never use telnet, but SSL telnet should be just as secure as password SSH.

What's the point of SSL telnetd, because one could just use ssh? You still have to bring in some heavy crypto libraries (openssl) so 'telnets' isn't any more lightweight solution either. The only reason I can think of is some corporate policy that dictates the use of telnet, and for some reason SSL is approved but ssh, that hacking tool, isn't.

Maybe because of the PKI features of SSL?

For instance...with an SSH client, the first time you contact a new server you're asked to verify the remote host's identity. I bet most of us just blindly type 'y' at this point despite the security implications. On the other hand, with SSL, you can have the server cert signed by a CA the client trusts.

OpenSSH supports PKI-based authentication and server certificate signing as of 5.4. Very useful in big enterprises and higher-security environment.

http://blog.habets.pp.se/2011/07/OpenSSH-certificates

Very cool, thanks for the info.

SSL telnet was created (May 2004) when SSH was not particularly popular yet.

SSH was actively replacing telnet in the late 90's already in any decent institution. At universities it was pretty much the standard. (At least on my side of the globe.)

> Ok, but no one uses telnetd, right?

No. Telnet is heavily used in industrial environments.

This makes me so scared.

Hopefully they have the intelligence to firewall it off, and only allow LAN use of telnet. Hopefully.

There are also a fair number of soho [wireless] routers with telnet enabled by default.

I guess that's partly due to memory footprint, or assumed memory footprint (dropbear being fairly small), by the manufacturers, and partly due to windows not having a ssh client by default, whereas every major OS comes with a telnet client.

Keep in mind that for some reason they default-disabled the telnet client on Vista and later.

Debian popcon says they have 371 people using it regularly.

For those who don’t know, “popcon” is short for Debian Popularity Contest, a project that collects stats about the usage of Debian packages from users who have installed the optional popcon package.

http://popcon.debian.org/

Anyone know if the other BSDs share this code?

According to comments on Colin's message, all BSDs as the bug has been there for years. OpenBSD doesn't have telnetd in its base distribution (and I currently don't have access to my OpenBSD server to check on the ports).

How many hands are needed to count the people still using telnet for anything remotely? I can see embedded use in isolated LANs, but...

I hereby propose a change to memcpy to include a maxbytes parameter and an optional assert() if len exceeds it.

Might turn up a few interesting things.

memcpy's third argument is the maximum (additionally, the exact) number of bytes it will copy.

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