It's been said that what doesn't kill you makes you stronger: if so then
Debian must be very strong these days.
The recent attack on Debian's servers is well known. It has been well
documented and explained in detail. What remains to do is to consider the
aftermath; have lessons been learned?
Recall the sequence of events. In the month of November, an unknown person
developed a crack that exploited that now famous kernel flaw and found his
way into a Debian developer's machine. Although it's not known if the
attack was focused on the developer's machine in particular, it was quickly
understood by the attacker that this PC presented a means to accessing the
Debian servers. He installed the requisite tools that took over the
machine and sniffed out the passwords. The attacker then obtained the
password that enabled him to compromise a Debian project server. In quick
succession, he penetrated a number of machines which spanned North-America
and Europe.
It must be understood that up to this point the attack had not been
detected. The machines were penetrated
and had been successfully subverted. The attacks were executed in such a
manner that none of the installed security mechanisms caught the
activity. So why didn't the archives get compromised? And how was it that
the attack, was even discovered?
The hand-crafted kernel exploit was not perfect. According to a group of
Debian contributors who were interviewed at a recent Linux User's Group
meeting (LUG), the exploit worked on all of the Intel machines but failed
against one Sparc system, which is where the archives happen to reside. Another
crack imperfection was that it generated strange messages in the log files
which led to the attack's discovery. It turns out that one of the system
administrators became uneasy as he was looking through the log files of
one of his machines. He quickly understood that the messages were not
normal and
the other machines were checked out in short order. This is how the attack
and its point of entry (the developer's compromised machine) were
discovered.
What are the lessons learned?
Crackers can make bad code: the existence of those log messages
indicates a lack of professionalism and sloppiness that eventually led to
the attack's discovery.
The bio-diversity of mixed environments defeats mono-culture
weaknesses: it's easy to criticize the fragility attributed by the
dominance of a Microsoft centric work environment. But we seemed to have
missed the fact that a Linux-only environment is monoculture too. Things
could have been worse if it wasn't for the inherent differences between
Intel and Sun System architectures.
Good people make a difference: a sharp brain and active curiosity are
a great combination. Given the time and resources, all exploits can be
caught.
Has anything been learned from this event that can help us formulate a more
proactive policy? That answer depends on how much we, the open source
community, are willing to work to eliminate these violations. These kinds
of people can exploit a hundred machines before they stumble over one that
can really hurt us. And that's the irony, for every attack that is noticed
there are ten more that are unseen. By increasing the diversity of our
systems and the alertness of our administration, we improve our chances of
detecting and shutting down this sort of attack before it does real
damage.
Stable CVS 1.11.10 has
been released, fixing a security issue with no known exploits (as of
this writing) that could cause previous versions of CVS to attempt to
create files and directories in the filesystem root. This release also
fixes several issues relevant to case insensitive filesystems and some
other bugs.
An advisory has gone out warning of a
remotely exploitable heap overflow vulnerability in rsync versions 2.5.6
and prior. If you are running an rsync server, you will want to apply a
distributor patch or upgrade to 2.5.7 in the near future.
Several security issues have been discovered affecting the Linux kernel:
CAN-2003-0461: /proc/tty/driver/serial reveals the exact character
counts for serial links. This could be used by a local attacker to infer
password lengths and inter-keystroke timings during password entry.
CAN-2003-0462: Paul Starzetz discovered a file read race condition
existing in the execve() system call, which could cause a local crash.
CAN-2003-0464: A recent change in the RPC code set the reuse flag on
newly-created sockets. Olaf Kirch noticed that his could allow normal
users to bind to UDP ports used for services such as nfsd.
CAN-2003-0476: The execve system call in Linux 2.4.x records the file
descriptor of the executable process in the file table of the calling
process, allowing local users to gain read access to restricted file
descriptors.
CAN-2003-0501: The /proc filesystem in Linux allows local users to
obtain sensitive information by opening various entries in /proc/self
before executing a setuid program. This causes the program to fail to
change the ownership and permissions of already opened entries.
CAN-2003-0550: The STP protocol is known to have no security, which
could allow attackers to alter the bridge topology. STP is now turned
off by default.
CAN-2003-0551: STP input processing was lax in its length checking,
which could lead to a denial of service.
CAN-2003-0552: Jerry Kreuscher discovered that the Forwarding table
could be spoofed by sending forged packets with bogus source addresses
the same as the local host.
Another buffer overflow in Apache 2.0.47 and earlier in mod_cgid's
mishandling of CGI redirect paths could result in CGI output going to the
wrong client when a threaded MPM is used.
CAN-2003-0789.
A problem was discovered in Apache2 where CGI scripts that write more than
4k to the standard error stream will hang the script's execution. This problem can lead to a
denial of service situation. See this bug
report for additional details.
Paul Mitcheson reported a situation where the CUPS Internet Printing
Protocol (IPP) implementation in CUPS versions prior to 1.1.19 would get
into a busy loop. This could result in a denial of service. In order to
exploit this bug an attacker would need to have the ability to make a TCP
connection to the IPP port (by default 631).
Multiple vulnerabilities have been found in
ethereal versions below 0.9.16. Remote attackers can craft
packets, and local users can build corrupt trace files,
resulting denial of service and remote code execution.
"fam" (file alteration monitor) watches files and directories for changes and lets interested applications know when something happens. This package has a flaw in its group handling that blocks some legitimate operations while, at the same time, exposing the names of files that should otherwise be invisible.
There is, it seems, an integer overflow vulnerability in "ls" which can be exploited via wu-ftpd to create a denial of service situation. See this advisory from Georgi Guninski for details.
DNS stub resolvers from multiple vendors contain a buffer overflow
vulnerability. The impact of this vulnerability appears to be limited to
denial of service. (See CERT Vulnerability Note
VU#738331)
The BIND 4 and BIND 8.2.x stub resolver libraries, and other libraries such
as glibc 2.2.5 and earlier, libc, and libresolv, uses the maximum buffer
size instead of the actual size when processing a DNS response, which
causes the stub resolvers to read past the actual boundary ("read buffer
overflow"), allowing remote attackers to cause a denial of service
(crash).
A severe vulnerability was discovered in GnuPG by Phong Nguyen relating to
ElGamal sign+encrypt keys. This
email message from Werner Koch contains more information. "Phong
Nguyen identified a severe bug in the way GnuPG creates and uses ElGamal
keys for signing. This is a significant security failure which can lead to
a compromise of almost all ElGamal keys used for signing. Note that this
is a real world vulnerability which will reveal your private key within a
few seconds."
GtkHTML is the HTML rendering widget used by the Evolution mail reader.
GtkHTML supplied with versions of Evolution prior to 1.2.4 contain a bug
when handling HTML messages. Alan Cox discovered that certain malformed
messages could cause the Evolution mail component to crash.
A vulnerability was discovered in the Linux kernel versions 2.4.22 and
previous. A flaw in bounds checking in the do_brk() function can allow a
local attacker to gain root privileges. This vulnerability is known to be
exploitable.
The 2.4.23 kernel contains the fix. For more details on how this vulnerability works, see this LWN article.
The kernel-utils package contains several utilities that can be used to
control the kernel or machine hardware. In Red Hat Linux 8.0 this package
contains user mode linux (UML) utilities.
The uml_net utility in kernel-utils packages with Red Hat Linux 8.0 was
incorrectly shipped setuid root. This could allow local users to control
certain network interfaces, add and remove arp entries and routes, and put
interfaces in and out of promiscuous mode.
All users of the kernel-utils package should update to these packages that
contain a version of uml_net that is not setuid root.
Alternatively, as a work-around to this vulnerability issue the following
command as root:
libnids (a NIDS plugin which emulates the Linux 2.0 IP stack) contains a buffer overflow vulnerability which can be exploited remotely. Version 1.18 fixes the problem.
Glenn Randers-Pehrson discovered a problem in connection with 16-bit
samples from libpng, an interface for reading and writing PNG
(Portable Network Graphics) format files. The starting offsets for
the loops are calculated incorrectly which causes a buffer overrun
beyond the beginning of the row buffer.
A remotely exploitable buffer overflow vulnerability was found in
MPlayer. A malicious host can craft a harmful ASX header, and trick MPlayer
into executing arbitrary code upon parsing that header. Read the full advisory
for details.
Some some vulnerabilities exsist in the Nessus NASL scripting engine. To
exploit these flaws, an attacker would need to have a valid Nessus account
as well as the ability to upload arbitrary Nessus plugins in the Nessus
server (this option is disabled by default) or he/she would need to trick a
user somehow into running a specially crafted nasl script. Read the full
advisory for additional information.
The Net-SNMP project includes various Simple Network Management Protocol
(SNMP) tools. A security issue in Net-SNMP versions before 5.0.9 could
allow an existing user/community to gain access to data in MIB objects that
were explicitly excluded from their view.
Version 5.0.9 of Net-SNMP is not vulnerable to this issue. In addition,
Net-SNMP 5.0.9 fixes a number of other minor bugs.
Linux NFS utils package contains remotely exploitable off-by-one bug.
A local or remote attacker could exploit this vulnerability by sending
specially crafted request to rpc.mountd daemon. See this BugTraq post for more details.
From the advisory:
"During a pen-test we stumbled across a nasty bug in OpenSSH-portable
with PAM support enabled (via the --with-pam configure script switch). This
bug allows a remote attacker to identify valid users on vulnerable systems,
through a simple timing attack. The vulnerability is easy to exploit and
may have high severity, if combined with poor password policies and other
security problems that allow local privilege escalation."
Pan is a Gnome/GTK+ newsreader. A bug in Pan versions prior to 0.13.4 can
cause Pan to crash when parsing an article header containing a very long
author email address. This bug causes a crash (denial of service) but is
not further exploitable.
The postfix MTA, versions through 1.1.12 (but not 2.0) is subject to two remotely exploitable denial of service vulnerabilities; see this advisory from Michal Zalewski for details.
The ASCII translation mechanism in ProFTPD 1.2.8 contains a vulnerability which will provide a remote attacker with a root shell - if the attacker is able to download a specially-crafted file. See this ISS advisory for more information.
usePerl has a
description of a vulnerability in the Safe.pm Perl module. It seems
that if a Safe compartment is used more than once, it ceases to be safe.
The problem is fixed in Safe 2.08.
Alexander Hvostov, Julien Blache and Aurelien Jarno discovered several
security-related problems in the sane-backends package, which contains
an API library for scanners including a scanning daemon (in the
package libsane) that can be remotely exploited. These problems allow
a remote attacker to cause a segfault fault and/or consume arbitrary
amounts of memory. The attack is successful, even if the attacker's
computer isn't listed in saned.conf.
You are only vulnerable if you actually run saned e.g. in xinetd or
inetd. If the entries in the configuration file of xinetd or inetd
respectively are commented out or do not exist, you are safe.
Try "telnet localhost 6566" on the server that may run saned. If you
get "connection refused" saned is not running and you are safe.
The Common Vulnerabilities and Exposures project identifies the
following problems:
CAN-2003-0773: saned checks the identity (IP address) of the remote
host only after the first communication took place (SANE_NET_INIT). So
everyone can send that RPC, even if the remote host is not allowed to
scan (not listed in saned.conf).
CAN-2003-0774: saned lacks error checking nearly everywhere in the
code. So connection drops are detected very late. If the drop of the
connection isn't detected, the access to the internal wire buffer leaves
the limits of the allocated memory. So random memory "after" the wire
buffer is read which will be followed by a segmentation fault.
CAN-2003-0775: If saned expects strings, it mallocs the memory
necessary to store the complete string after it receives the size of the
string. If the connection was dropped before transmitting the size,
malloc will reserve an arbitrary size of memory. Depending on that size
and the amount of memory available either malloc fails (->saned quits
nicely) or a huge amount of memory is allocated. Swapping and OOM
measures may occur depending on the kernel.
CAN-2003-0776: saned doesn't check the validity of the RPC numbers
it gets before getting the parameters.
CAN-2003-0777: If debug messages are enabled and a connection is
dropped, non-null-terminated strings may be printed and segmentation
faults may occur.
CAN-2003-0778: It's possible to allocate an arbitrary amount of
memory on the server running saned even if the connection isn't dropped.
At the moment this can not easily be fixed according to the author.
Better limit the total amount of memory saned may use (ulimit).
According to
this advisory a buffer overflow in GNU screen allows privilege
escalation for local users. Usually screen is installed either setgid-utmp
or setuid-root.
It also has some potential for remote attacks or getting control of another
user's screen. The problem is that you have to transfer around 2-3 gigabytes
of data to user's screen to exploit this vulnerability. 4.0.1, 3.9.15 and
older versions are vulnerable.
A vulnerability was discovered in stunnel versions 3.24 and earlier, as
well as 4.00, by Steve Grubb. It was found that stunnel leaks a critical
file descriptor that can be used to hijack stunnel's services. See this
advisory for more information.
The tar utility does not properly filter file names containing
"../", meaning that a hostile archive can, if unpacked by an
unsuspecting user, overwrite any file that is writable by that user. GNU
tar versions 1.13.19 and earlier are vulnerable; unzip through version 5.42
has the same vulnerability.
This vulnerability,
originally thought to be confined to BSD-derived systems, was first covered
in the July 26th Security
Summary. It is now known that Linux telnet daemons are vulnerable as
well.
VIM allows a user to set the modeline differently for each edited text file
by placing special comments in the files. Georgi Guninski found that these
comments can be carefully crafted in order to call external programs. This
could allow an attacker to create a text file such that when it is opened
arbitrary commands are executed.
Zebra an open source implementation of TCP/IP routing software.
Jonny Robertson reported that Zebra can be remotely crashed if a Zebra
password has been enabled and a remote attacker can connect to the Zebra
telnet management port. The Common Vulnerabilities and Exposures project
(cve.mitre.org) has assigned the name CAN-2003-0795 to this issue.
Herbert Xu reported that Zebra can accept spoofed messages sent on the
kernel netlink interface by other users on the local machine. This could
lead to a local denial of service attack. The Common Vulnerabilities and
Exposures project (cve.mitre.org) has assigned the name CAN-2003-0858 to
this issue.
The Open Source Software Institute has posted a FAQ describing the
current OpenSSL FIPS 140-2 validation effort. This work, which is
sponsored by HP and the Defense Medical Logistics Standard Support
program of the DoD Military Health System, seeks to have the OpenSSL
cryptographic modules certified as complying with the FIPS 140-2 standard.
At that point, it would be possible for vendors to create applications
which carry the same validation. See the document for lots of details.
The 2004 version of the Black Hat Briefings will be held in Amsterdam on
May 17 to 20. The call for papers is out now, with a submission
deadline of March 25.
