Ubuntu Forums are back up and a post mortem

As announced previously, there was a security breach on the Ubuntu Forums. The Ubuntu Forums are now back up and running. What follows is a detailed post mortem of the breach and corrective actions taken by the Canonical IS team. In summary, the root cause was a combination of a compromised individual account and the configuration settings in vBulletin, the Forums application software. There was no compromise of Ubuntu itself, or any other Canonical or Ubuntu services. We have repaired and hardened the Ubuntu Forums, and as the problematic settings are the default behaviour in vBulletin, we are working with vBulletin staff to change and/or better document these settings.

What happened

At 16:58 UTC on 14 July 2013, the attacker was able to log in to a moderator account owned by a member of the Ubuntu Community.

This moderator account had permissions to post announcements to the Forums. Announcements in vBulletin, the Forums software, may be allowed to contain unfiltered HTML and do so by default.

The attacker posted an announcement and then sent private messages to three Forum administrators (also members of the Ubuntu community) claiming that there was a server error on the announcement page and asking the Forum administrators to take a look.

One of the Forum administrators quickly looked at the announcement page, saw nothing wrong and replied to the private message from the attacker saying so. 31 seconds after the Forum administrator looked at the announcement page (and before the administrator even had time to reply to the private message), the attacker logged in as that Forum administrator.

Based on the above and conversations with the vBulletin support staff, we believe the attacker added an XSS attack in the announcement they posted which sent the cookies of any visitor to the page to the attacker.

Once the attacker gained administrator access in the Forums they were able to add a hook through the administrator control panel. Hooks in vBulletin are arbitrary PHP code which can be made to run on every page load. The attacker installed a hook allowing them to execute arbitrary PHP passed in a query string argument. They used this mechanism to explore the environment and also to upload and install two widely available PHP shell kits. The attacker used these shell kits to upload and run some custom PHP code to dump the ‘user’ table to a file on disk which they then downloaded.

The attacker returned on 20 July to upload the defacement page.

What the attacker could access

The attacker had full access to the vBulletin environment as an administrator and shell access as the ‘www-data’ user on the Forums app servers.

Having administrator access to the vBulletin environment means they were able to read and write to any table in the Forums database.

They used this access to download the ‘user’ table which contained usernames, email addresses and salted and hashed (using md5) passwords for 1.82 million users.

What the attacker could not access

We believe the attacker was NOT able to escalate past the ‘www-data’ user (i.e. gain root access) on the Forums app servers.

We believe the attacker was NOT able to escalate past remote SQL access to the Forums database on the Forums database servers.

We believe the attacker did NOT gain any access at all to the Forums front end servers.

We believe the attacker was NOT able to gain any access to any other Canonical or Ubuntu services.

We know the attacker was NOT able to gain access to any Ubuntu code repository or update mechanism.

What we don’t know

We don’t know how the attacker gained access to the moderator account used to start the attack.

The announcement the attacker posted was deleted by one of the Forum administrators so we don’t know exactly what XSS attack was used.

What we’ve done

Before bringing the Forums back online, we implemented a series of changes both designed to clean up after this attack and also to defend against and mitigate the fallout from possible attacks in the future.

Clean up

• We sent individual mails to all Forums users informing them of the breach and that they should consider their Forum password compromised. We advised them to change this password on any other systems where they may have re-used it.
• We backed up the servers running vBulletin, and then wiped them clean and rebuilt them from the ground up.
• We randomised all user passwords in the Forums.
• We reset all system and database passwords.
• We manually imported data into a fresh database after sanity checking each table.

Hardening

• We’ve removed the ability to modify or add new hooks except via root access to the database
• We’ve disabled all potential HTML posting avenues in the Forums for everyone but administrators.
• We’ve switched the Forums to use Ubuntu SSO for user authentication.
• We’ve implemented automated expiry of inactive moderator and administrator accounts.
• We’ve confined vBulletin with an AppArmor profile.
• We’ve reviewed and further hardened the firewalling around the Forums servers.
• We’ve reviewed and further hardened the PHP config on the server to close off some vectors used by the attacker.
• We’ve switched to forcing HTTPS for the administrator and moderator control panels and made it optionally available everywhere else
• We’ve improved escalation procedures for the Ubuntu Community members who graciously volunteer their time to administer and moderate the Forums.
• We will continue to work with vBulletin staff to discuss changes to the default settings which could help others avoid similar scenarios as this. The vBulletin support staff have been helpful and cooperative throughout this incident.

Finally, we’d like once again to apologize for the security breach, the data leak and downtime.