Two weeks ago, this page examined
SQL injection attacks on web applications. Another well-known attack
is cross-site scripting, often abbreviated as "XSS." Cross-site scripting
is, perhaps, a more subtle way of breaking web applications, but its
effects can be just as damaging as SQL Injection.
The basic vector for XSS is user input into a website that is not
filtered to remove dangerous content. One of the more obvious ways this
can occur is with sites that allow users to add comments to stories,
without removing or altering HTML tags that they enter.
For example, if one adds a comment that contains:
<script>alert("howdy")</script>
and someone else, when looking at that comment, gets the alert,
the site is vulnerable to XSS. Obviously, a javascript popup is not
particularly dangerous and would be a clear sign that something odd is
going on. This kind of 'attack' is only used as a proof of concept.
The key thing to note
is that one user can run javascript in the context of another user's
browser, with all of the information and privileges of the targeted user
(or, at least, the subset granted to javascript).
There are other mechanisms to inject this kind of malicious content, either
as HTML links or by causing error messages that display the content.
Essentially any
place that a web application displays user input can be exploited if the
input or output is not filtered correctly. When XSS attacks appear in links,
they are often encoded in hex using the '%xx' or '&#xx;' so that it is not
immediately apparent that the link contains malicious content.
A wide variety of actions can be triggered by an XSS exploit, including
cookie theft, account hijacking, and denial of service. A clever attacker
could make a page that looks exactly like the login page of a popular website
(Google for example) and an unwary user could be fooled into
entering their username and password into this page after following a link.
By exploiting an XSS hole recently
reported
and discussed
on the Bugtraq mailing list, the link would not obviously be malicious and
could start with http://www.google.com.
Another common attack is to hijack a session by using an XSS exploit to
capture a cookie value that
stores a session ID. An
attacker can then use that session ID to take over a currently logged-in
session at the web site and for all intents and purposes, become that
user. This attack is especially nasty if that user happens to be an administrative
user - or is logged into, say, a financial site.
Avoiding XSS in a web application requires diligence in filtering user input
(a common theme in nearly all web application vulnerabilities). Any user
input that is sent back to browser for any reason needs to have certain
characters converted to strings that will display properly, but not be
interpreted as HTML by the browser. An XSS
FAQ
recommends replacing the following characters: < > ( ) & and #
with <, >, (, etc.
XSS vulnerabilities are one of the most commonly reported security issues
with web applications today. New XSS techniques are discovered regularly
that find new ways to evade various security measures implemented by
the browser scripting languages and new ways to fool users into falling
into an XSS trap.
Any technique that allows attackers to run code
in your browser with your permissions is obviously cause for worry. Website
users can only take some fairly drastic measures to avoid XSS (turning off
javascript, not following links, etc.). This is clearly something that
website owners must handle to protect their users.
Users of the ClamAV free anti-virus system should be aware of the
recent vulnerabilities
in that package. No need to fear, however:
SonicWALL has announced that its (proprietary) anti-virus system is now equipped to shield your network from attempts to exploit one of those vulnerabilities. So ClamAV users need not actually apply the update - just layer another anti-virus package on top of it instead.
The ClamAV anti-virus toolkit has three vulnerabilities.
the PE header parser has an integer overflow problem,
the logging code has format string vulnerabilities that may lead
to the execution of arbitrary code, and
the cli_bitset_set() function can be used to create a denial
of service.
The libimager-perl Perl extension has a vulnerability
in which maliciously created 4-channel JPEG images
can cause a segmentation fault and cause a denial of service.
MPlayer 1.0pre7try2 has multiple integer overflow vulnerabilities.
Remote attackers can maliciously craft an ASF file or an AVI file
in order to cause a denial of service.
OpenVPN 2.0 through 2.0.5 allows remote malicious servers to execute
arbitrary code on the client by using setenv with the LD_PRELOAD
environment variable.
From the Debian advisory: "It was discovered that the Plone content management system lacks security
declarations for three internal classes. This allows manipulation of user
portraits by unprivileged users."
In some cases, xscreensaver did not properly grab the keyboard when
reading the password for unlocking the screen, so that the password
was typed into the currently active application window. The only known
vulnerable case was when xscreensaver activated while an rdesktop session
was currently active.
Andy Staudacher discovered that ADOdb does not properly sanitize all
parameters. By sending specifically crafted requests to an application
that uses ADOdb and a PostgreSQL backend, an attacker might exploit the
flaw to execute arbitrary SQL queries on the host.
Versions 1 and 2 of the apache web server suffer from a cross-site scripting vulnerability in the mod_imap module; see this bugzilla entry for details.
Damian Put discovered that Blender did not properly validate a 'length'
value in .blend files. Negative values led to an insufficiently sized
memory allocation. By tricking a user into opening a specially crafted
.blend file, this could be exploited to execute arbitrary code with the
privileges of the Blender user.
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.
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).
It was discovered that Crossfire, a multiplayer adventure game, performs
insufficient bounds checking on network packets when run in "oldsocketmode",
which may possibly lead to the execution of arbitrary code.
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-imapd, prior to version 2.2.12, contains several buffer overflows which could be exploited by an (authenticated) attacker to run code on the server system.
Joxean Koret discovered that the SVG import plugin did not properly
sanitize data read from an SVG file. By tricking an user into opening
a specially crafted SVG file, an attacker could exploit this to
execute arbitrary code with the privileges of the user.
Three buffer overflows were discovered in the Xfig file format importer.
By tricking a user into opening a specially crafted .fig file with dia, an
attacker could exploit this to execute arbitrary code with the user's
privileges.
Max Vozeler discovered a format string vulnerability in the "movemail"
utility of Emacs. By sending specially crafted packets, a malicious
POP3 server could cause a buffer overflow, which could be exploited to
execute arbitrary code with the privileges of the user and the "mail"
group.
Erik Sjölund has discovered several security relevant problems in enscript,
a program to convert ASCII text into Postscript and other formats.
Unsanitized input can cause the execution of arbitrary commands via EPSF
pipe support. Due to missing sanitizing of filenames it is possible that a
specially crafted filename can cause arbitrary commands to be executed.
Multiple buffer overflows can cause the program to crash.
Fetchmail contains a bug which allows a malicious mail server to crash the
client by sending a message without headers. This occurs when running in
multidrop mode.
There is a vulnerability in the foomatic-filters package. This
vulnerability is due to insufficient checking of command-line parameters
and environment variables in the foomatic-rip filter. This vulnerability
may allow both local and remote attackers to execute arbitrary commands on
the print server with the permissions of the spooler.
An unspecified vulnerability in FreeRADIUS 1.0.0 up to 1.1.0 allows remote
attackers to bypass authentication or cause a denial of service (server
crash) via "Insufficient input validation" in the EAP-MSCHAPv2 state
machine module.
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.
Another vulnerability has been found in
GnuPG. "Signature verification of non-detached signatures may give a
positive result but when extracting the signed data, this data may be
prepended or appended with extra data not covered by the signature. Thus
it is possible for an attacker to take any signed message and inject extra
arbitrary data."
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.
Versions of horde prior to 3.1.1 have two vulnerabilities, both of which are remotely exploitable: code execution in the help viewer and an input validation error which could allow read access to arbitrary files.
A buffer overflow flaw was found in the c-client IMAP client. An attacker
could create a malicious IMAP server that if connected to by a victim could
execute arbitrary code on the client machine.
ipsec-tools has a remote
denial of service vulnerability in the racoon daemon.
If racoon is running in aggressive mode, it fails to check all peer
payloads during
When the daemon the IKE negotiation phase, allowing a malicious peer
to crash the daemon. One should always be careful around aggressive racoons.
Marcus Meissner discovered that kaffeine, a media player for
KDE 3, contains an unchecked buffer that can be overwritten remotely
when fetching remote RAM playlists which can cause the execution of
arbitrary code.
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.
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.
A number of vulnerabilities have been found in the Linux kernel, including a PPP-related denial of service problem, an integer overflow in the epoll() code, memory corruption in the ELF loader, and exploitable overflows in the ISO9660 code.
Here's another set of vulnerabilities in the Linux kernel:
A race condition in the 2.6 kernel could allow a local user to cause a
DoS by triggering a core dump in one thread while another thread has a
pending SIGSTOP (CVE-2005-3527).
The ptrace functionality in 2.6 kernels prior to 2.6.14.2, using
CLONE_THREAD, does not use the thread group ID to check whether it is
attaching to itself, which could allow local users to cause a DoS
(CVE-2005-3783).
The auto-reap child process in 2.6 kernels prior to 2.6.15 include
processes with ptrace attached, which leads to a dangling ptrace
reference and allows local users to cause a crash (CVE-2005-3784).
A locking problem in the POSIX timer cleanup handling on exit on
kernels 2.6.10 to 2.6.14 when running on SMP systems, allows a local
user to cause a deadlock involving process CPU timers (CVE-2005-3805).
The IPv6 flowlabel handling code in 2.4 and 2.6 kernels prior to
2.4.32 and 2.6.14 modifies the wrong variable in certain circumstances,
which allows local users to corrupt kernel memory or cause a crash by
triggering a free of non-allocated memory (CVE-2005-3806).
An integer overflow in 2.6.14 and earlier could allow a local user to
cause a hang via 64-bit mmap calls that are not properly handled on a
32-bit system (CVE-2005-3808).
An algorithm weakness has been discovered in Apache2::Request, the
generic request library for Apache2 which can be exploited remotely
and cause a denial of service via CPU consumption.
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.
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.
Mailman 2.1.5 and below have a denial of service vulnerability
in the Scrubber.py script. If a maliciously created message
with a mime multi part format is received, mailman delivery
can be stopped.
mod_python has a vulnerability in the publisher handler that may allow
a remote user to use a specially crafted URL to allow access to
objects that should be protected. An information leak can result.
Mozilla has three new vulnerabilities.
The Javascript interpreter has a problem with
dereferencing objects. A user can visit a specially crafted web page
which can crash the browser or cause it to execute arbitrary code.
The XULDocument.persist() function has a bug that can be triggered by
viewing specially crafted web sites, RDF data can be injected into the
localstore.rdf file, allowing arbitrary javascript code to be executed.
The Mozilla history saving mechanism is vulnerable to a denial of
service attack, visiting sites with extra-long titles can cause a
crash or very slow startup the next time the browser is run.
The WYSIWYG rendering engine in Mozilla Thunderbird 1.0.7 and earlier
allows user-complicit attackers to bypass javascript security settings and
obtain sensitive information or cause a crash via an e-mail containing a
javascript URI in the SRC attribute of an IFRAME tag, which is executed
when the user edits the e-mail.
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.
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.
Erik Sjolund discovered two vulnerabilities in the programs bundled
with ncpfs: there is a potentially exploitable buffer overflow in
ncplogin (CAN-2005-0014), and due to a flaw in nwclient.c, utilities
using the NetWare client functions insecurely access files with
elevated privileges (CAN-2005-0013).
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.
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.
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 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).
HTTP requests with conflicting Content-Length and Transfer-Encoding headers
could lead to HTTP Request Smuggling Attack, which can be exploited to
bypass packet filters or poison web caches.
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.
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.
Webmail.php in SquirrelMail 1.4.0 to 1.4.5 allows remote attackers to
inject arbitrary web pages into the right frame via a URL in the
right_frame parameter. NOTE: this has been called a cross-site scripting
(XSS) issue, but it is different than what is normally identified as
XSS. (CVE-2006-0188)
Interpretation conflict in the MagicHTML filter in SquirrelMail 1.4.0 to
1.4.5 allows remote attackers to conduct cross-site scripting (XSS) attacks
via style sheet specifiers with invalid (1) "/*" and "*/" comments, or (2)
a newline in a "url" specifier, which is processed by certain web browsers
including Internet Explorer. (CVE-2006-0195)
CRLF injection vulnerability in SquirrelMail 1.4.0 to 1.4.5 allows remote
attackers to inject arbitrary IMAP commands via newline characters in the
mailbox parameter of the sqimap_mailbox_select command, aka "IMAP
injection." (CVE-2006-0377)
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.
The rsvp_print function in tcpdump 3.9.1 and earlier allows remote
attackers to cause a denial of service (infinite loop) via a crafted RSVP
packet of length 4. (CAN-2005-1280)
tcpdump 3.8.3 and earlier allows remote attackers to cause a denial of
service (infinite loop) via a crafted BGP packet, which is not properly
handled by RT_ROUTING_INFO, or LDP packet, which is not properly
handled by the ldp_print function. (CAN-2005-1279)
The isis_print function, as called by isoclns_print, in tcpdump 3.9.1 and
earlier allows remote attackers to cause a denial of service (infinite
loop) via a zero length, as demonstrated using a GRE packet.
(CAN-2005-1278)
The teTeX PDF parsing library has an integer overflow vulnerability.
A carefully crafted PDF file can be used by an attacker to crash
teTeX and possibly execute arbitrary code.
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 PHP-based webcalendar package suffers from three vulnerabilities: a set of SQL injection problems (CVE-2005-3949), an input sanitizing failure allowing local files to be overwritten (CVE-2005-3961), and a response splitting vulnerability (CVE-2005-3982).
Shaun Colley discovered a problem in xine-ui, the xine video player
user interface. A script contained in the package to possibly remedy
a problem or report a bug does not create temporary files in a secure
fashion. This could allow a local attacker to overwrite files with
the privileges of the user invoking xine.
Three buffer overflows were discovered in xloadimage when handling the image title name. A malicious user can construct a NIFF file that when viewed and processed (with either zoom, reduce or rotate) by xloadimage, will cause the program to overwrite the return address and execute arbitrary code.
Derek Noonburg has fixed several potential vulnerabilities in xpdf,
which are also present in gpdf, the Portable Document Format (PDF)
viewer with Gtk bindings.
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.
David A. Wheeler has posted the
slides from his "open standards and security" talk [PDF]. When
viewing, skip immediately to the middle, where you can find a second set of
slides with added commentary. "In contrast, open standards make
security possible. They enable continuous competition between suppliers, so
you can now choose the supplier who provides adequate security. Suppliers
now compete on security, so they will have to improve. The key is using
open standards appropriately to enable competition."
