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Date: Tue, 2 Dec 2003 15:23:51 +0100
From: Martin Schulze <joey@infodrom.org>
To: Debian Announcements <debian-announce@lists.debian.org>
Subject: Debian Investigation Report after Server Compromises
Resent-Date: Tue, 2 Dec 2003 08:45:03 -0600 (CST)
Resent-From: debian-announce@lists.debian.org
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The Debian Project
http://www.debian.org/
Debian Investigation Report
press@debian.org
December 2nd, 2003
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- --
Debian Investigation Report after Server Compromises
The Debian administration team and security experts are finally able
to pinpoint the method used to break-in into four project machines.
However, the person who did this has not yet been uncovered.
The package archives were not altered by the intruder.
The Debian administration and security teams have checked these
archives (security, us, non-us) quite early on in the investigation
and re-installation process. That's why the project was able to open
up the security archive again and confirm that the stable update
(3.0r2) wasn't compromised.
If the project had anticipated to get compromised at the same time
the
stable update was implemented, the involved people would have
postponed it. However, the updated packages were already installed
in
the stable archive and mirror servers at the time the break-ins were
discovered, so it wasn't possible to hold it back anymore.
Several methods based on different control data were used to verify
the packages and to ensure that the archives weren't altered by the
attacker:
. externally stored lists of MD5 sums accumulated over the past
weeks
on not compromised machines
. digitally signed .changes files from external debian-devel-changes
archives on not compromised machines
. digitally signed .changes files on the respective archive servers
. externally stored mirror log files
Timeline
Below is the timeline of discovery and recovery of the compromised
machines. All times are in UTC. Some times are only estimates since
our conversation did not contain exact timestamps.
Sep 28 01:33 Linus Torvalds releases 2.6.0-test6 with do_brk()
fix
Oct 02 05:18 Marcello Tosatti applies do_brk() boundary check
Nov 19 17:00 Attacker logs into klecker with sniffed password
Nov 19 17:08 Root-kit installed on klecker
Nov 19 17:20 Attacker logs into master with same sniffed
password
Nov 19 17:47 Root-kit installed on master
Nov 19 18:30 Attacker logs into murphy with service account from
master
Nov 19 18:35 Root-kit installed on murphy
Nov 19 19:25 Oopses on murphy start
Nov 20 05:38 Oopses on master start
Nov 20 20:00 Discovery of Oopses on master and murphy
Nov 20 20:54 Root-kit installed on gluck
Nov 20 22:00 Confirmation that debian.org was compromised
Nov 21 00:00 Deactivation of all accounts
Nov 21 00:34 Shut down security.debian.org
Nov 21 04:00 Shut down gluck (www, cvs, people, ddtp)
Nov 21 08:30 Point www.debian.org to www.de.debian.org
Nov 21 10:45 Public announcement
Nov 21 16:47 Developer information updated
Nov 21 17:10 Shut down murphy (lists)
Nov 22 02:41 security.debian.org is back online
Nov 25 07:40 lists.debian.org is back online
Nov 28 22:39 Linux 2.4.23 released
Discovery
On the evening (GMT) of Thursday, November 20th, the admin team
noticed several kernel oopses on master. Since that system was
running without problems for a long time, the system was about to be
taken into maintenance for deeper investigation of potential hardware
problems. However, at the same time, a second machine, murphy, was
experiencing exactly the same problems, which made the admins
suspicious.
Also, klecker, murphy and gluck have "Advanced Intrusion Detection
Environment" (package aide) installed to monitor filesystem changes
and at around the same time it started warning that /sbin/init had
been replaced and that the mtime and ctime values for
/usr/lib/locale/en_US had changed.
Further investigation revealed the cause for both these problems to
be
the SucKIT root-kit. It includes password sniffing and detection
evasion capabilities (i.e. tools to hide processes and files) which
are installed directly into the kernel, which in turn caused the
oopses that were noticed.
Detailed Attack Analysis
On Wednesday, November 19th, at approximately 5pm GMT, a sniffed
password was used to log into an unprivileged developer account on
the
host klecker (.debian.org). The attacker then retrieved the source
code through HTTP for an (at that time) unknown local kernel exploit
and gained root permissions via this exploit. Afterwards, the SucKIT
root-kit was installed.
The same account and password data were then used to log into the
machine master, to gain root permissions with the same exploit and
also to install the SucKIT root-kit.
The attacker then tried to get access to the host murphy with the
same
account. This failed because murphy is a restricted machine and its
only purpose is to act as list server to which only a small subset of
developers can log into. Since the initial login attempt didn't work
the person used his root access on master to access an administrative
account which was used for backup purposes and gained access to
murphy
as well. The SucKIT root-kit was installed on this host as well.
On the next day the attacker used a password sniffed on master to log
into gluck, get root there and also install the SucKIT root-kit.
The forensic analysis revealed exact dates and times when the program
/sbin/init was overwritten and the root-kit installed. The analysts
also discovered the executable file which was used to gain root
access
on the machines, which was protected and obfuscated with Burneye.
Upon unwrapping and disassembling the exploit, security experts
discovered which kernel bug was utilised.
An integer overflow in the brk system call was exploited to overwrite
kernel memory (change page protection bits). By doing so the
attacker
gained full control about the kernel memory space and was able to
alter any value in memory.
Even though this kernel bug was discovered in September by Andrew
Morton and already fixed in recent pre-release kernels since October,
its security implication wasn't considered that severe. Hence, no
security advisories were issued by any vendor. However, after it was
discovered to be used as a local root exploit the Common
Vulnerabilities and Exposures project has assigned CAN-2003-0961 to
this problem. It is fixed in Linux 2.4.23 which was released last
weekend and in the Debian advisory DSA 403.
Linux 2.2.x is not vulnerable to this exploit because boundary
checking is done before. It is also believed that Sparc and PA-RISC
kernels are not vulnerable since user and kernel addresses are stored
in different address spaces on these architectures.
Please understand that we cannot give away the used exploit to random
people who we don't know. So please don't ask us about it.
Recovery
After the machines were shut down, images of the compromised hard
disks were created and stored on a separate machine. They were
distributed to the people doing the forensic analysis. The three
machines in the US (master, murphy, gluck) were reinstalled
afterwards
and their services re-instated one by one after investigation by the
relevant service admin.
On klecker, however, this was postponed for a scheduled maintenance
so
the security archive could be brought online again sooner than the
other services. At that time we also didn't have console access to
klecker, so recovery had to be done remotely. After a disk-image was
made via serial console login to a local machine on a firewalled
network connection, the root-kit was removed, the kernel exchanged
and
hardened, binaries double-checked and the security archive verified
against several different external sources. This machine will be
reinstalled in the next few weeks.
As a security precaution all developer accounts were disabled in LDAP
and SSH keys removed on the more important machines, so that no more
machines could be compromised. This, however, effectively disabled
just about any public Debian work that involved uploading files and
accessing the CVS repositories.
All passwords used on quantz (i.e. all Alioth, arch and subversion
passwords) have been invalidated as well. All SSH authorized keys
have been removed as well. Please use the lost password system to
receive a new password at:
https://alioth.debian.org/account/lostpw.php
When all services are running again and the machines are sufficiently
secured, LDAP will be reset so that developers can create a new
password again (<http://db.debian.org/password.html>). It can't
currently be predicted when this will happen, though.
Upon recovery SSH was reinstalled on the compromised machines.
Hence, there are new RSA host keys and key fingerprints for these
hosts. The keys will be included in LDAP as soon as they are created
and can be taken from <http://db.debian.org/machines.cgi>.
Consequences
!! Renew your passwords! !!
Since passwords were sniffed on the compromised hosts, any outgoing
connection that involved a password is to be considered compromised
as
well, i.e. the password should be considered known to the attacker.
It should therefore be changed immediately.
Additionally, if somebody had access to a Debian machine and was
using
the same password or passphrase on other machines or keys we strongly
advise to change the password or passphrase respectively as soon as
possible.
If an SSH key was generated or stored on one of these machines and
was
used to log into other machines (i.e. by installing it in
.ssh/authorized_keys), it should be removed as well.
The secret GnuPG/PGP keys which were found on debian.org machines
were
also removed from the Debian keyrings and thus deactivated.
Developers who are worried about their own machines should at least
run chkrootkit and watch its output. Matt Taggert maintains a
backport of the current version for woody at the following address:
deb http://lackof.org/taggart/debian woody/chkrootkit main
deb-src http://lackof.org/taggart/debian woody/chkrootkit main
Additionally, a detailed list of precaution issues is provided by
Wichert Akkerman and Matt Taggart at:
http://www.wiggy.net/debian/developer-securing/
SucKIT Root-Kit
SucKIT is a root-kit presented in Phrack issue 58, article 0x07
("Linux on-the-fly kernel patching without LKM", by sd & devik).
This
is a fully working root-kit that is loaded through /dev/kmem, i.e. it
does not need a kernel with support for loadable kernel modules. It
provides a password protected remote access connect-back shell
initiated by a spoofed packet (bypassing most firewall
configurations), and can hide processes, files and connections.
Usually, SucKIT is launched as /sbin/init at system bootup, forks to
install itself into the kernel, start up a backdoor, and launches a
copy of the original "init" binary from the parent (with pid 1). Any
subsequent executions of /sbin/init are redirected to the original
init.
TESO's Burneye Protection
Burneye is a means of obfuscating ELF binaries on the UNIX platform
presented in Phrack issue 58, article 0x05 ("Armouring the ELF:
Binary
encryption on the UNIX platform", by grugq & scut). Using tools like
TESO's Burneye, an attacker can alter an executable program to
encrypt
its true purpose, hiding it from firewall filters, intrusion
detection
systems, anti-virus software and the prying eyes of investigators.
Thanks
. James Troup and Ryan Murray for their general work on all hosts
. Adam Heath and Brian Wolfe for their work on master and murphy
. Wichert Akkerman for his work on klecker
. Dann Frazier and Matt Taggart for their work on gluck
. Michael Stone and Robert van der Meulen for their forensics work
. Marcus Meissner for disassembling the used exploit
. Jaakko Niemi for his work on checking and re-enabling
lists.debian.org
. Colin Watson for his work on checking and re-enabling
bugs.debian.org
. Josip Rodin for his work on checking and re-enabling the lists
web
archives
Contact Information
For further information, please visit the Debian web pages at
<http://www.debian.org/> or send mail to <press@debian.org>.
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