Over the past two weeks, this page has looked at two of the more widely
known proposals for improving the email infrastructure:
Sender Policy Framework (SPF) and
Domain Keys (DK).
This week will conclude the series by
looking at a few lesser known proposals and describe the kinds of problems
they are meant to solve.
Due to
joe jobs and other
spammer tricks, sites can sometimes be overwhelmed with bounce messages
from emails that they did not send. Two proposals provide ways for
the receivers of bounce messages (i.e. the domain that purportedly sent
the original message) to recognize invalid bounces before accepting the email.
Both
Signed
Envelope Sender (SES) and
Bounce Address Tag Validation (BATV)
are focused on eliminating invalid bounce messages.
Both techniques rely on using a uniquely generated envelope sender
for each outgoing mail, typically with a one-way hash or cryptographic
mechanism that can be verified by the sending Mail Transfer Agent (MTA).
When a bounce message arrives, it will have a null envelope sender
(to prevent loops) and an envelope recipient. If the MTA cannot verify
the envelope recipient as one of the uniquely generated addresses, it can
reject the email before receiving the DATA portion. This protection against
invalid bounce messages is one that can be unilaterally implemented by a
sending domain and will benefit that domain without requiring any
cooperation from other MTAs.
Both SES and BATV have ways to generate envelope sender addresses that
allow intermediary MTAs to verify the sender and determine if the email
was truly sent by the domain that purports to have sent it. In addition,
any hosts that use
SMTP sender address verification will be able to reject forged email
envelope sender addresses in domains that use SES/BATV because the
verification will fail for addresses that are not correctly generated.
Certified Server Validation (CSV)
is a technique that can arguably replace all of the trust evaluation that
SPF provides, but can do it in a more straightforward manner. By using the
hostname given in the SMTP HELO/EHLO command and a SRV record that has been
queried from the DNS, a receiving MTA can determine if the sending host has
correctly identified itself. In addition, the DNS record will indicate
whether the host is authorized to transfer mail for the domain.
All of the proposals and techniques that have been described in these three
articles are incremental changes to thwart one or more deficiencies in the
original design of SMTP. Because it was designed at a time when there were
few, if any, malicious users of the internet, security and authentication
were not major considerations.
More radical, non-incremental, changes to
how email is handled, such as Daniel J. Bernstein's
Internet Mail 2000 (IM2000)
have been proposed, but would require a wholesale shift in MTA and Mail
User Agent (MUA) software to implement them. Instead of email receivers
storing messages, IM2000 requires senders to store the messages and, at
least partially, attempts to burden the sender with
the costs of the email, rather than today's system which really only
burdens the recipient.
A descendant of IM2000
called
Differentiated
Mail Transfer Protocol (DMTP) is currently being worked on as a
potential internet standard.
Even if some SMTP alternative were to become an internet standard, it
remains to be seen how many users and mail servers would make the switch.
SMTP has a huge amount of inertia behind it and any replacement is likely to
be a long time in coming and have an adoption rate reminiscent of
IPv6.
A bug in EnergyMech fails to handle empty CTCP NOTICEs correctly, and
will cause a crash from a segmentation fault. By sending an empty CTCP
NOTICE, a remote attacker could exploit this vulnerability to cause a
denial of service.
Andreas Seltenreich has reported a possible heap overflow in the
array_push() function in hashcash.c, as a result of an incorrect amount
of allocated memory for the "ARRAY" structure.
There is a race condition error in the "posix-cpu-timers.c" script that
does not prevent another CPU from attaching the timer to an exiting
process. This could be exploited by attackers to cause a denial of
service.
A flaw due to errors in "powerpc/kernel/signal_32.c" and
"powerpc/kernel/signal_32.c" could allow userspace to provoke a machine
check on 32-bit kernels.
An infinite loop in "netfilter/xt_sctp.c" could be exploited by attackers
to exhaust all available memory resources, creating a denial of service
condition.
TAKAHASHI Tamotsu discovered that mutt's IMAP backend did not sufficiently
check the validity of namespace strings. If an user connects to a malicious
IMAP server, that server could exploit this to crash mutt or even execute
arbitrary code with the privileges of the mutt user. See this Secunia advisory for more
information.
Mysqld in MySQL 4.1.x before 4.1.18, 5.0.x before 5.0.19, and 5.1.x before
5.1.6 allows remote authorized users to cause a denial of service (crash)
via a NULL second argument to the str_to_date function.
Pinball, a pinball game simulator, has a privilege escalation
vulnerability in which the application can be tricked into loading
level plugins from user-controlled directories without dropping
its privileges.
artswrapper in aRts, when running setuid root on Linux 2.6.0 or later
versions, does not check the return value of the setuid function call,
which allows local users to gain root privileges by causing setuid to fail,
which prevents artsd from dropping privileges.
The Asterisk PBX application has a buffer overflow vulnerability in the
IAX2 channel driver that can be used for the remote execution of
arbitrary code.
The GNU Binutils has a buffer overflow vulnerability in libbfd.
Maliciously crafted Tektronix Hex Format files with improper length
characters can cause a crash and possibly lead to the execution of
arbitrary code.
The BusyBox 1.1.1 passwd command does not use a proper salt when generating
passwords. This would create an instance where a brute force attack could
take very little time.
A race condition in bzip2 1.0.2 and earlier allows local users to modify
permissions of arbitrary files via a hard link attack on a file while it is
being decompressed, whose permissions are changed by bzip2 after the
decompression is complete. Also specially crafted bzip2 archives may cause
an infinite loop in the decompressor.
From the Debian-Testing alert: Mehdi Oudad "deepfear" and Kevin Fernandez "Siegfried" from the Zone-H
Research Team discovered a buffer overflow in kkstrtext.h of the ktools
library, which is included in (at least) centericq and motor.
A denial of service vulnerability has been found in the function for
encoding email addresses. Addresses containing a '=' before the '@'
character caused the Courier to hang in an endless loop, rendering the
service unusable.
Richard Harms discovered that cpio did not sufficiently validate file
properties when creating archives. Files with e. g. a very large size
caused a buffer overflow. By tricking a user or an automatic backup
system into putting a specially crafted file into a cpio archive, a
local attacker could probably exploit this to execute arbitrary code
with the privileges of the target user (which is likely root in an
automatic backup system).
The Vixie cron daemon does not check the return code from setuid(); if that call can be made to fail, a local attacker may be able to execute commands as root.
A buffer overflow in Cscope 15.5, and possibly multiple overflows, allows
remote attackers to execute arbitrary code via a C file with a long
#include line that is later browsed by the target.
Heap-based buffer overflow in cURL and libcURL 7.15.0 through 7.15.2 allows
remote attackers to execute arbitrary commands via a TFTP URL (tftp://)
with a valid hostname and a long path.
Cyrus-SASL contains an unspecified vulnerability in the DIGEST-MD5
process that could lead to a Denial of Service. An attacker could possibly
exploit this vulnerability by sending specially crafted data stream to the
Cyrus-SASL server, resulting in a Denial of Service even if the attacker is
not able to authenticate.
The FreeType library has several integer overflow vulnerabilities.
If a user can be tricked into installing a specially
crafted font file, arbitrary code can be executed with the privilege
of the user.
Tavis Ormandy of the Gentoo Linux Security Audit Team discovered an integer
overflow in the BFD library, resulting in a heap overflow. A review also
showed that by default, gdb insecurely sources initialization files from
the working directory. Successful exploitation would result in the
execution of arbitrary code on loading a specially crafted object file or
the execution of arbitrary commands.
A format string vulnerability has been discovered in gedit. Calling
the program with specially crafted file names caused a buffer
overflow, which could be exploited to execute arbitrary code with the
privileges of the gedit user.
A vulnerability was discovered in GnuPG 1.4.3 and 1.9.20 (and earlier) that
could allow a remote attacker to cause gpg to crash and possibly overwrite
memory via a message packet with a large length.
zgrep in gzip before 1.3.5 does not handle shell metacharacters like '|'
and '&' properly when they occurred in input file names. This could be
exploited to execute arbitrary commands with user privileges if zgrep is
run in an untrusted directory with specially crafted file names.
The Horde3 web application framework does not perform sufficient
input sanitizing, allowing the possible injection of web
script code through a cross-site scripting attack.
The ImageMagick DisplayImageCommand has a heap overflow vulnerability.
If an maliciously created unexpanded glob is passed to ImageMagick,
a heap overflow can result.
The kdebase package (and kcheckpass in particular) found in KDE versions 3.2.0 through 3.4.2 suffers from a lock file handling error which can enable a local attacker to obtain root access. See this advisory for details.
The KDE Display Manager(KDM) is vulnerable to a local symlink attack.
A local user can use this to read arbitrary files that they do not
have permission to access. See this KDE
advisory for more information.
Kate / Kwrite, as shipped with KDE 3.2.x up to including 3.4.0, creates a file backup before saving a modified file. These backup files are created with default permissions, even if the original file had more strict permissions set. See this advisory for more information.
Multiple vulnerabilities in the Linux have been found.
An error in the Stream Control Transmission Protocol (SCTP) code that
uses incorrect state table entries when certain ECNE chunks are received in
CLOSED state, could be exploited by attackers to cause a kernel panic via a
specially crafted packet.
An error exist when handling incoming IP-fragmented SCTP control
chunks, which could be exploited by attackers to cause a kernel panic via a
specially crafted packet.
Linux SCTP (lksctp) allows remote attackers to cause a denial of
service (infinite recursion and crash) via a packet that contains two or
more DATA fragments, which causes an skb pointer to refer back to itself
when the full message is reassembled, leading to infinite recursion in the
sctp_skb_pull function
Linux SCTP (lksctp) allows remote attackers to cause a denial of
service (deadlock) via a large number of small messages to a receiver
application that cannot process the messages quickly enough, which leads to
"spillover of the receive buffer."
A vulnerability has been identified due to an input validation error
when processing arguments containing backslash ("\\") characters passed to
certain commands (e.g. "cd"), which could be exploited by authenticated
attackers to escape chroot restrictions for a CIFS or SMBFS mounted
filesystem.
The 2.6.12 kernel has a remote memory corruption vulnerability
that can be remotely triggered by loading the ip_nat_snmp_basic
module and traffic is network-translated on port 161 or 162.
Szymon Zygmunt and Michal Bartoszkiewicz discovered a memory alignment
error in libgadu (from ekg, console Gadu Gadu client, an instant
messaging program) which is included in gaim, a multi-protocol instant
messaging client, as well. This can not be exploited on the x86
architecture but on others, e.g. on Sparc and lead to a bus error,
in other words a denial of service.
Several buffer overflows have been discovered in libgd's PNG handling
functions.
If an attacker tricked a user into loading a malicious PNG image, they
could leverage this into executing arbitrary code in the context of
the user opening image. Most importantly, this library is commonly
used in PHP. One possible target would be a PHP driven photo website
that lets users upload images. Therefore this vulnerability might lead
to privilege escalation to a web server's privileges.
Multiple buffer overflows in the gd graphics library (libgd) 2.0.21 and
earlier may allow remote attackers to execute arbitrary code via malformed
image files that trigger the overflows due to improper calls to the
gdMalloc function.
libpam-ldap, the PAM LDAP interface, has a vulnerability in which
it fails to authenticate with an LDAP server which is not configured
properly, allowing an authentication bypass.
A heap based buffer overflow bug was found in the way libpng strips alpha
channels from a PNG image. An attacker could create a carefully crafted PNG
image file in such a way that it could cause an application linked with
libpng to crash or execute arbitrary code when the file is opened by a
victim.
The t2p_write_pdf_string function in libtiff 3.8.2 and earlier is vulnerable
to a buffer overflow. Attackers can use a TIFF file with UTF-8 characters
in the DocumentName tag to overflow a buffer, causing a denial of service,
and possibly the execution of arbitrary code.
Yuuichi Teranishi discovered a flaw in libxml2 versions prior to 2.6.6.
When fetching a remote resource via FTP or HTTP, libxml2 uses special
parsing routines. These routines can overflow a buffer if passed a very
long URL. If an attacker is able to find an application using libxml2 that
parses remote resources and allows them to influence the URL, then this
flaw could be used to execute arbitrary code.
libxml2 prior to version 2.6.14 has multiple buffer overflow
vulnerabilities, if a local user passes a specially crafted
FTP URL, arbitrary code may be executed.
An arbitrary command execute bug was found in the lynx "lynxcgi:" URI
handler. An attacker could create a web page redirecting to a malicious URL
which could execute arbitrary code as the user running lynx.
MySQL 5.0.18 and earlier allows local users to bypass logging mechanisms
via SQL queries that contain the NULL character, which are not properly
handled by the mysql_real_query function. NOTE: this issue was originally
reported for the mysql_query function, but the vendor states that since
mysql_query expects a null character, this is not an issue for mysql_query.
Stefano Di Paola discovered an information leak in the login packet
parser. By sending a specially crafted malformed login packet, a
remote attacker could exploit this to read a random piece of memory,
which could potentially reveal sensitive data. (CVE-2006-1516)
Stefano Di Paola also found a similar information leak in the parser
for the COM_TABLE_DUMP request. (CVE-2006-1517)
Kurt Fitzner discovered that the NBD (network block device) server did not
correctly verify the maximum size of request packets. By sending specially
crafted large request packets, a remote attacker who is allowed to access
the server could exploit this to execute arbitrary code with root
privileges.
When starting xntpd with the -u option and specifying the
group by using a string not a numeric gid the daemon uses
the gid of the user not the group. This problem is now fixed
by this update.
OpenLDAP is vulnerable to a stack-based buffer overflow in the
st.c file from slurpd. Attackers may be able to use a long hostname
to execute arbitrary code.
The libUil component of the OpenMotif toolkit has a pair of buffer
overflow vulnerabilities that can possibly be used for the execution
of arbitrary code.
PAM-MySQL has multiple vulnerabilities involving the
handling of pam_get_item() results and other unspecified issues,
this can be used for a denial of service attack, users can be
prevented from logging in.
There are two vulnerabilities with perl when it is used in a setuid mode. The PERLIO_DEBUG environment variable can be used to overwrite arbitrary files; there is also an associated buffer overflow which can be exploited to gain root access.
The php wordwrap() function is vulnerable to an integer overflow.
Attackers can submit long arguments to cause a heap-based buffer
overflow, allowing arbitrary code execution.
PHP 5.x and PHP 4.4.2 have a problem with the substr_compare() function.
An attacker can use an out-of-bounds offset argument to cause a
memory access violation, causing a denial of service.
A bug in zend_hash_del() allowed attackers to prevent unsetting of some variables
It was discovered that phpbb2, a web based bulletin board, insufficiently
sanitizes values passed to the "Font Color 3" setting, which might lead to
the execution of injected code by admin users.
The phpbb2 web forum has a number of vulnerabilities including:
a web script injection problem, a protection mechanism bypass, a
security check bypass, a remote global variable bypass, cross site
scripting vulnerabilities, an SQL injection vulnerability,
a remote regular expression modification problem, missing input
sanitizing, and a missing request validation problem.
Stefan Esser reported multiple vulnerabilities
found in phpMyAdmin. The $GLOBALS variable allows modifying the global
variable import_blacklist to open phpMyAdmin to local and remote file
inclusion, depending on your PHP version (CVE-2005-4079, PMASA-2005-9).
Furthermore, it is also possible to conduct an XSS attack via the
$HTTP_HOST variable and a local and remote file inclusion because the
contents of the variable are under total control of the attacker
(CVE-2005-3665, PMASA-2005-8).
The PostgreSQL team has put out a set of "urgent updates" (in the form of the 7.3.15, 7.4.13, 8.0.8, and 8.1.4 releases) closing a
newly-discovered set of SQL injection issues. Details about the problem
can be found on the
technical information page; in short: multi-byte encodings can be used
to defeat normal string sanitizing techniques. The update fixes one problem
related to invalid multi-byte characters, but punts on another by simply
disallowing the old, unsafe technique of escaping single quotes with a
backslash.
Py2Play uses Python pickles to send objects over a peer-to-peer game network, that clients accept without restriction the objects and code sent by peers. A remote attacker participating in a Py2Play-powered game can send
malicious Python pickles, resulting in the execution of arbitrary
Python code on the targeted game client.
Paul Jakma discovered that Quagga's ripd daemon did not properly
handle authentication of RIPv1 requests. If the RIPv1 protocol had
been disabled, or authentication for RIPv2 had been enabled, ripd
still replied to RIPv1 requests, which could lead to information
disclosure. (CVE-2006-2223)
Paul Jakma also noticed that ripd accepted unauthenticated RIPv1
response packets if RIPv2 was configured to require authentication and
both protocols were allowed. A remote attacker could exploit this to
inject arbitrary routes. (CVE-2006-2224)
Fredrik Widell discovered that Quagga did not properly handle certain
invalid 'sh ip bgp' commands. By sending special commands to Quagga, a
remote attacker with telnet access to the Quagga server could exploit
this to trigger an endless loop in the daemon (Denial of Service).
(CVE-2006-2276)
Luigi Auriemma discovered multiple flaws in the Scorched 3D game
server, including a format string vulnerability and several buffer
overflows. A remote attacker could exploit these vulnerabilities to crash
a game server or execute arbitrary code with the rights of the game server
user.
Sendmail has a vulnerability in the way it handles multi-part MIME messages.
A remote attacker can create a specially crafted email message that can
be used to crash the sendmail process, causing a denial of service.
The useradd tool from the shadow-utils package has a potential security
problem. When a new user's mailbox is created, the permissions are
set to random garbage from the stack, potentially allowing the
file to be read or written during the time before fchmod() is called.
A buffer overflow in UnZip 5.50 and earlier allows local users to execute
arbitrary code via a long filename command line argument. NOTE: since the
overflow occurs in a non-setuid program, there are not many scenarios under
which it poses a vulnerability, unless unzip is passed long arguments when
it is invoked from other programs.
xtensive testing of libwww's handling of multipart/byteranges content from
HTTP/1.1 servers revealed multiple logical flaws and bugs in
Library/src/HTBound.c
The wv2 library, which is used to access Microsoft Word documents,
has a boundary checking error that can be used to create an integer
overflow when processing word files.
Federico L. Bossi Bonin discovered a buffer overflow in the HTTP input
module. By tricking an user into opening a malicious remote media
location, a remote attacker could exploit this to crash Xine library
frontends (like totem-xine, gxine, or xine-ui) and possibly even
execute arbitrary code with the user's privileges.
xine-lib does an improper input data boundary check on
MPEG streams. A specially crafted MPEG file can be
created that can cause arbitrary code execution when the
file is accessed.
Several format string vulnerabilities have been discovered in xine-ui,
the user interface of the xine video player, which may cause a denial
of service.
There is a buffer overflow in the Xrender extension of the X.Org server; any process which is able to connect to the server may be able to exploit this overflow to run arbitrary code. Since the X server runs as root on most systems, this vulnerability could be exploited to gain root access. See the X.Org advisory for more information.
A flaw was discovered in Xpdf in that could allow an attacker to construct
a carefully crafted PDF file that would cause Xpdf to consume all available
disk space in /tmp when opened.
xpdf has a number of integer overflows.
A remote attacker can trick a user into opening a maliciously
crafted pdf file, allowing the attacker to execute code with the
privileges of the local user.
This also affects the Poppler library, cupsys and tetex-bin.
