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Re: [Xen-users] Web Console Access

To: Felix Kuperjans <felix@xxxxxxxxxxxxxxxxxx>, Xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Web Console Access
From: Jonathan Tripathy <jonnyt@xxxxxxxxxxx>
Date: Sat, 19 Jun 2010 19:48:46 +0100
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Hi Felix,

I'm currently testing out my ajaxterm + ssh idea (with ajaxterm running on the webserver) and I've run into a small problem.

When you do, for example ping xx.xx.xx.xx from with an xm console "session", CTRL-C doesn't stop the pinging. Instead, it exits out of the ssh process. This happens regardless if I use ajaxterm or just do direct ssh.

Any ideas?

Many Thanks

On 19/06/10 11:04, Felix Kuperjans wrote:
Hi Jonathan,

I think this would increase the risk if ajaxterm would not be secure enough and you will need SSH anyway... I'll have a look at ajaxterm now:

(Note that I only read their website, did not test it locally)

- Ajaxterm seems to contain an own little webserver, which is usually proxied through apache2 (or other Webservers) for SSL encryption and port access. I think you won't be able to use PHP sessions here! Httpauth would be possible, indeed.
- Many applications nowadays require UTF-8 locales (e.g. python3 AFAIK) to have their full functionality, but ajaxterm only handles latin1. As long as the language is English, most letters will have the same UTF-8 and latin1-codes, but it would not support some special characters in the terminal (even © would be a problem).
- I'd say that the dom0 should only use SSH, but I'd really reconsider if you need a web console. SSH can be easily accessed with Windows, Linux and Mac and offers really secure encryption and authentication mechanisms.

I don't think that the ability to restrict the access to Dom0's services (SSH / ajaxterm) with a firewall is a big pro:
If the users get access via apache2 to Dom0's ajaxterm or via ajaxterm on the webserver to Dom0's SSH, exploits will be usable as well via that proxy (for example, worst case: xm console would have a bug that would allow command execution with xm's rights (root!) within Domain-0 on a special key combination - it would work either way, but such severe bugs have never existed in the history of XEN).

Try out some SSH-based setups, I personally prefer them to any web-based solution (restart / shutdown etc. can still be handled with a web-interface). If you like, I could help you with SSH configuration / hardening.

Regards,
Felix

Am 19.06.2010 11:22, schrieb Jonathan Tripathy:
Hi Felix,

I have another idea to maybe make it easier to implement:

Instead of running Ajaxterm locally on the web server, I could run it on the xen host itself. Inside the vif script, everytime the VM starts up, I could put in a line that starts ajaxterm and binds it to a port which is specific to that user. Then, I could use iptables to make sure that the only machine which has access to this port is the web server.

Then on the web server, php could handle all the authentication, and then "proxy" the ajaxterm output from the xen host to the user. No ssh keys required!

Pros:
Easy to start/stop ajaxterm by using the vif scripts
Easy to firewall (just use iptables)

Cons:
Lots of ajaxterms will be launched (1 per vm), so the xen host may not handle this very well
The web server will need to use ssh anyway for startup/shutdown/restart of VMs

What you think?

Thanks


On 18/06/10 16:11, Felix Kuperjans wrote:
Hm I don't know of an actual hack when the session is SSL encrypted, but it's not a good practise to send the login credentials every time although they are encrypted.
Safe session ids, are better because there is one login with the password and the 'password' for further requests is the session id (which must be at least as safe then, preferably even safer), combined with a three tries for the password mechanism or something similar.
Best method are HMAC's, but as far as I know, this is not available on PHP, but the default for SSH or OpenVPN connections.

suhosin adds many security improvements to PHP (even to the default session mechanism) and I think it should be preferred over htaccess.

Regards,
Felix

Am 18.06.2010 17:01, schrieb Jonathan Tripathy:
Thanks Felix.
 
What you think of the Apache htaccess method?
 
Thanks


From: Felix Kuperjans [mailto:felix@xxxxxxxxxxxxxxxxxx]
Sent: Fri 18/06/2010 15:54
To: Jonathan Tripathy
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Web Console Access

My main security concern would be rather:
If I were your customer, I would want that my VM's console is completely secured. But just relying on PHP sessions or HTTP-auth is not really secure, e.g.:

http://www.h-online.com/open/news/item/PHP-blunders-with-random-numbers-967525.html

A hacker could abuse such insecure mechanisms of PHP to enter the session with a well-guessed session-id. PHP Auth resends all login credentials every time a request is made, and so there is no real session, which makes attacks sometimes easier. Of course, the security of those applications can be improved (especially with suhosin), but webservers and web-frontends are the primary hacking target (and very often subject to vulnerabilities).

I wouldn't doubt that it will *work* with that method, but having it in a secure way will be harder (but still possible).

Probably you should consider using an own session mechanism, but this will require an advanced and security-aware PHP programmer. /dev/random (or if necessary /dev/urandom) should definitely be used for gaining the entropy for the session id and it should be long enough and further secured by ip address. And remember to do that all on a SSL-only connection, using that without SSL would allow anyone to do MITM attacks to capture the password / session id.

Regards,
Felix

Am 18.06.2010 16:30, schrieb Jonathan Tripathy:
 
Thanks Felix,
 
Glad you like my idea. Since ajaxterm runs its own web server (and you can specify the port is listens on, which would be one per customer), I think it's just a matter of using php to control access to this resource.
 
Another, easier way, would be to just use Apache's .htaccess stuff (No sessions required). Just protect one directory per user, and in each directory simply have an index.php that runs the correct ajaxterm command for the user. Then Apache could use it's reverse proxy mechanism to give the user access to ajax term. The "logical" address of the ajax term would be a child of the inital htaccess protected directory. This isn't as nice and doesn't scale well, but I'm pretty sure it would work..


From: Felix Kuperjans [mailto:felix@xxxxxxxxxxxxxxxxxx]
Sent: Fri 18/06/2010 15:25
To: Jonathan Tripathy
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Web Console Access

Hi Jonathan,

I think this is a great idea: The Domain-0 has full SSH-security (can be limited to your webserver's internal ip address for further security) and the webserver is not running on Dom0.
You could combine this approaches:
SSH on Dom0, with RSA authentification and (for example) sudo-wrapped xm console, accessed by your ajaxterm software. It would be even possible to provide both methods to your customers, if the SSH daemon is secured enough, or just allow that web console. When the web console is secure enough, this will not expose any security threats to your customers, and it would never be a threat to your Dom0s. You'll need to ask the ajaxterm developers, I only know that many PHP session ids are *not* safely generated and ajax can even extend that problem (on the other hand, suhosin fixes that problem). SSH's HMAC-method is more safe, but many applications rely on PHP's safety (some of them without being hacked), so it would offer enough security if the application has no big security issues.

Regards,
Felix

Am 18.06.2010 16:09, schrieb Jonathan Tripathy:
Hi Felix,
 
What I was thinking of doing (And i'll need to consult with my php/java folk here to get this working in a secure way), is to run Ajaxterm on the web server itself. When launch Ajaxterm, there is a -c option that allows you to specify a command. With an ssh key stored in the web server's filesystem (Which only is allowed to preform global xm functions), I could do something like (The command would run locally on the web server):
 
./ajaxterm.py -c ssh xmuser@xxxxxxxxxxxxxxxxxxxx -k /path/to/key xm console $vm_id
 
Where $vm_id could be storaed in a database and would be the name of the DomU running 
 
What you think?


From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx on behalf of Felix Kuperjans
Sent: Fri 18/06/2010 14:57
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Web Console Access

Hi Jonathan,

if you can do that, it's good. But you'll always need some kind of access to the Dom0 to get the console data and to reboot / reset / rescue the VMs (whatever you want to offer to your customers).

Regards,
Felix

Am 18.06.2010 15:17, schrieb Jonathan Tripathy:
Hi Felix,
 
Probably the main reason why I want to use a web console is so that I can run the web server on a different machine (Or maybe in a VM connected to an isolated network).
 
Thanks for the tip on the Grub password for the Dom0. That's scary about the KVM!
 
Thanks
 
Jonathan


From: Felix Kuperjans [mailto:felix@xxxxxxxxxxxxxxxxxx]
Sent: Fri 18/06/2010 14:13
To: Jonathan Tripathy
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Web Console Access

Hi Jonathan,

the Dom0 cannot be compromised as long as your SSH or web-based console does not have any security leaks.
PHP sessions are not as secure as SSH, but with SSL and suhosin patched PHP considerably OK.

As I said, I don't use web-based consoles so I can't help you there, but I'd *really* consider whether it is a good thing to setup a webserver on a Dom0 and it may be probably hard to do web-based consoles without that.

Regards,
Felix

P.S. Anyway, considering the method I posted, you should always setup GRUB and BIOS passwords for all of your Dom0s. I once requested KVM access at my provider and ended up at the wrong server...

Am 18.06.2010 15:03, schrieb Jonathan Tripathy:
Hi Felix,
 
I actually have that guy's book who wrote that article - The book of Xen - very good book indeed!
 
What I really wish to do, is provide a similar sort of thing to that SSH setup, except allow it to be accessed via a web browser. I have an idea where I can use ajaxterm and some PHP scripting. Once a user logs on with a username and password, I could tell php to start ajaxterm and piple xm console through it. This is what Slicehost does I think. The console would be protected with php sessions.
 
But my main worry was whether or not the Dom0 could be compramised via the above method, but I don't think that's the case.
 
Thanks
 
Jonathan

From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx on behalf of Felix Kuperjans
Sent: Fri 18/06/2010 13:50
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Web Console Access

Hi Jonathan,

this is a common way to reset lost / forgotton root passwords:

You need:
- Physical access to a machine (if you want to reset the password of the Dom0 or a native linux) or console access to a DomU
- Access to the kernel command line, via lilo, grub or pygrub/pvgrub in XEN

Then you do:
- Modify the kernel command line, add the init=/bin/bash option, for example: kernel /linux-2.6.32.15-xen root=/dev/xvda2 init=/bin/bash
- You'll directly end up in a root console without password or any services started after the kernel booted
- enter those commands:
mount -o remount,rw /
passwd root
<enter new password>
exec /sbin/init

The root password will then be the newly set one.

DomUs generally are not vulnerable to this method, as long as the kernel command line is set in the domain configuration. But pygrub/pvgrub is a nice thing for hosting customers, because they can compile their own kernels, containing their preferred settings, modules and builtin functionality. Generally this problem is avoided by adding a password to grub, but some customers may forget that step.
So physical access can always be a strong weapon, but it is necessary for repairing a machine or for some advanced setups (especially when setting up a firewall, one easily gets locked out of the server...). I think the best way is securing this access, by restricting virtual console access to highly encrypted and authenticated sessions (IMHO the best way is SSH here).

I'd also think about customers forgetting to log out, because leaving xm console does *not* logout root inside the console.

The tutorial I posted to your I/O question contains a SSH-based setup for xm console access with sudo, which may be nice to start with. I personally use an own wrapper inside a chroot jail, to provide the ability of entering commands like create / rescue / setup (rescue starts another domain configuration with NFS root + rescue-Kernel, setup starts a virtual Debian setup). It's quite handy for VPS customers.

Regards,
Felix

Am 18.06.2010 14:26, schrieb Jonathan Tripathy:
 
Hi Felix,
 
Thanks for the email.
 
>a simple init=/bin/bash added to the kernel command line allows resetting the root password...
ok this worries me. Can you please explain this a little further? Do you need to have access to the Dom0 to begin with?
 
Thanks


From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx on behalf of Felix Kuperjans
Sent: Fri 18/06/2010 12:54
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Web Console Access

Hi Jonathan,

do you definitely need a web console (so really browser-based) or would you consider a SSH-based console?

I personally prefer SSH because it is more secure, easier to set up and it is somehow the default way of accessing remote consoles. You can do a modified SSH setup that only allows access to the console, or optionally, access to xm console, xm list, xm shutdown, xm create but restricted to the own VM of your customer. With chroot-jails etc., other commands cannot be executed.
SSH also has the advantage of good copy & paste of larger commands, and the possibility to work with multiple client certificates and / or passwords. Probably your administrative interface allows uploading of multiple public keys, so that your customers can have multiple adminsitrative accounts for the server (but only one can access the console at a time).

I've got no experiences with ajaxterm, but you should really control its security:
Console access is quite useful for hackers, e.g. some customer may forget to log out root or if you use pvgrub / pygrub, a simple init=/bin/bash added to the kernel command line allows resetting the root password...
So it must be a really secure application, not vulnerable to XSS, SQL Injections, Connection hijacking, ... and SSL encrypted.

Regards,
Felix Kuperjans

Am 18.06.2010 13:02, schrieb Jonathan Tripathy:
Hi Everyone,
 
Does anyone have any idea on how to give my customers a "web console" for their VMs?
 
Using http://antony.lesuisse.org/software/ajaxterm/ I can manually set up a remote session for them, by doing
ajaxterm.py -c xm console <DOMNAME>
However is there any way to make this automatic? Maybe I could put it in the vif script?
 
Thanks
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