A certain amount of attention has recently been given to a spam-blocking
method called greylisting. A look
at the description of the technique shows that it does not, actually, have
much in the new way of ideas. Greylisting might, however, become a useful
part of the antispam arsenal at some sites.
The core idea of the greylisting technique has been around for a while. It
relies on the fact most spammers do not bother to track and retry
deliveries which are declined by the receiving system with a temporary
failure status. Real mail systems will retry the message later on, until
they run out of patience. Spammers just forget about it and move on. So
an effective way of blocking a large percentage of incoming spam is to
simply refuse mail from new sources with a temporary failure on the first
delivery attempt. Real mail will eventually show up again, and be
delivered with a small delay. Most spam will never return.
The greylisting technique uses a slightly finer-grained approach. It
creates a three-entry tuple out of the originating address, the sender, and
the recipient of the message. If the tuple is new, the mail is refused for
a configurable period of time. The use of the three-way tuple helps
prevent spam from slipping in by using false sender addresses.
The obvious workaround, from a spammer's point of view, is to add retrying
for temporary failures to their code. Given the desire of the spam
industry to pollute our mailboxes regardless of how hard we try to prevent
that, the implementation of temporary failure retrying is only a matter of
time. Of course, mail sent through open relays is generally retried
anyway, so widespread use of greylisting could result in more use of open
relays, and, perhaps, more attempts to compromise systems to turn them into
unwilling relays.
As the author describes it, greylisting is meant to be used in conjunction
with other spam-blocking techniques, especially blackhole lists. The hope
is that, by the time the temporary failure interval has ended for a
particular spam source, that source will have found its way into the
blacklists and the message can be blocked permanently. This combination
could, indeed, prove hard for the spammers to get around.
eldav, a WebDAV client for Emacs, creates temporary files without
taking appropriate security precautions. This vulnerability could be
exploited by a local user to create or overwrite files with the
privileges of the user running emacs and eldav.
Several security problems have been found in Ethereal
0.9.12. "It may be possible to make Ethereal crash or run
arbitrary code by injecting a purposefully malformed packet onto the wire,
or by convincing someone to read a malformed packet trace file."
Orville Write, a replacement for the standard write(1) command,
contains a number of buffer overflows. These could be exploited to
gain either gid tty or root privileges, depending on the configuration
selected when the package is installed.
Steve Kemp discovered that osh, a shell intended to restrict the
actions of the user, contains two buffer overflows, in processing
environment variables and file redirections. These vulnerabilities
could be used to execute arbitrary code, overriding any restrictions
placed on the shell.
webfs, a lightweight HTTP server for static content, contains a buffer
overflow whereby a long Request-URI in an HTTP request could cause
arbitrary code to be executed.
Steve Kemp discovered several buffer overflows in xbl, a game, which
can be triggered by long command line arguments. This vulnerability
could be exploited by a local attacker to gain gid 'games'. This has been assigned CVE #
CAN-2003-0451.
Another buffer overflow was discovered in xbl which could also be exploited by a local attacker to gain gid 'games'. This has been assigned CVE #
CAN-2003-0535.
A couple of new vulnerabilities have been found in the xterm application shipped with XFree86. There is yet another "execute arbitrary commands by setting the window title" vulnerability, along with a bug which can allow an attacker to lock up an exterm window.
From the Red Hat advisory: "A vulnerability has been discovered in the ypserv NIS server prior to
version 2.7. If a malicious client queries ypserv via TCP and subsequently
ignores the server's response, ypserv will block attempting to send the
reply. This results in ypserv failing to respond to other client requests." The fix is up upgrade to version 2.8.0.
The BIND 4.9.8-OW2 patch and BIND 4.9.9 release (and thus 4.9.9-OW1)
include fixes for a libc related vulnerability which does not
affect Linux. Updates from
the Internet Software Consortium (ISC)
are available from here.
No release or branch of Openwall GNU/*/Linux (Owl) is known to be
affected, due to Olaf Kirch's fixes for this problem getting into the
GNU C library more than two years ago.
Unfortunatly that does not mean that Linux systems are not vulnerable.
Similar code, without Olaf Firch's fixes,
is in the glibc getnetbyXXX functions.
These functions are described in the SuSE alert as
"
used by very few applications only, such as ifconfig and ifuser,
which makes exploits less likely."
CERT Advisory: CA-2002-19
Buffer Overflow in Multiple DNS Resolver Libraries
A Denial Of Service (DoS) vulnerability was discovered in BitchX that would
allow a remote attacker to crash BitchX by changing certain channel modes.
Read more
here and here.
Canna is a kana-kanji conversion server which is necessary for Japanese
language character input.
A buffer overflow bug in the Canna server up to and including version 3.5b2
allows a local user to gain the privileges of the user 'bin' which could
lead to further exploits. The Common Vulnerabilities and Exposures project
(cve.mitre.org) has assigned the name CAN-2002-1158 to this issue.
A lack of validation of requests has been found that affects Canna version
3.6 and earlier. A malicious remote user could exploit this vulnerability
to leak information, or cause a denial of service attack. (CAN-2002-1159)
Phil D'Amore of Red Hat discovered a vulnerability in the CUPS IPP
(Internet Printing Protocol) implementation. The IPP implementation is
single-threaded, which means only one request can be serviced at a time.
An attacker could make a partial request that does not time out and
therefore creates a denial of service. In order to exploit this bug, an
attacker must have the ability to make a TCP connection to the IPP port (by
default 631).
Timo Sirainen discovered several vulnerabilities in ethereal, a
network traffic analyzer. These include one-byte buffer overflows in
the AIM, GIOP Gryphon, OSPF, PPTP, Quake, Quake2, Quake3, Rsync, SMB,
SMPP, and TSP dissectors, and integer overflows in the Mount and PPP
dissectors.
"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.
Versions of fetchmail prior to 6.2.0 have (yet another) buffer overflow vulnerability which can be exploited remotely via a suitably crafted message. See this advisory for details.
Felix von Leitner, discovered a
potential division by zero bug in
code derived from the SunRPC library which is used in glibc.This bug could be
exploited to gain unauthorized root access to software linking to glibc.
Updating as soon as practical is a good idea.
Because SunRPC-derived XDR libraries are used by a variety of vendors in a variety of applications, this defect may lead to a number of differing security problems. Exploiting this vulnerability will lead to denial of service, execution of arbitrary code, or the disclosure of sensitive information.
CERT/CC Vulnerability Note VU#192995 Integer
overflow in xdr_array() function when deserializing the XDR stream
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).
Bas Wijnen discovered that the gnocatan server is vulnerable to
several buffer overflows which could be exploited to execute arbitrary
code on the server system.
A key validation bug was discovered in the GNU Privacy Guard (GPG) which
would cause keys with more then one user ID to trust all user ID's with the
amount of trust given to the most-valid user ID.
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.
The IMP IMAP server, versions 2.2.8 and prior, is vulnerable to SQL
injection; see this advisory for details.
Version 3.x is not vulnerable to this problem.
The KDE Security team has issued an advisory
on a vulnerability present in all versions of KDE that allow a remote
attacker to execute arbitrary commands under your account. KDE 3.0.5b and
KDE 3.1.1a have been released to address this problem. For KDE 2.2.2
patches to the KDE 2.2.2 sources have been made available.
KDE uses Ghostscript software for processing of PostScript (PS) and PDF
files in a way that allows for the execution of arbitrary commands that can
be contained in such files.
An attacker can prepare a malicious PostScript or PDF file which will
provide the attacker with access to the victim's account and privileges
when the victim opens this malicious file for viewing or when the victim
browses a directory containing such malicious file and has file previews
enabled.
An attacker can provide malicious files remotely to a victim in an e-mail,
as part of a webpage, via an ftp server and possible other means.
Versions 2.2.x and 2.4.x of the Linux kernel contain a vulnerability in
ptrace() which may be exploited by a local user to obtain root
access. This announcement contains the
details and a patch for 2.4.20. For 2.2 users, 2.2.25 has been released
which contains the fix.
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:
A vulnerability was discovered in versions of kopete
prior to 0.6.2. Kopete is a KDE instant messenger client. This
vulnerabiliy is in the GnuPG plugin that allows for users to send each
other GPG-encrypted instant messages. The plugin passes encrypted messages
to gpg, but does no checking to sanitize the commandline passed to gpg.
This can allow remote users to execute arbitrary code, with the permissions
of the user running kopete, on the local system.
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.
If lynx is given a url with some special characters on the command line, it
will include faked headers in the HTTP query. This feature can be used to
force scripts (that use Lynx for downloading files) to access the wrong
site on a web server with multiple virtual hosts.
Calle Dybedahl discovered a bug in lyskom-server which could result in
a denial of service where an unauthenticated user could cause the
server to become unresponsive as it processes a large query.
The SuSE Security Team reviewed critical Perl modules, including the
Mail::Mailer package. This package contains a security hole which allows
remote attackers to execute arbitrary commands in certain circumstances.
This is due to the usage of mailx as default mailer which allows commands
to be embedded in the mail body.
Note that mail processing programs which use this package can be affected by this vulnerability; in particular, SpamAssassin is vulnerable if you use the -r or -w flags.
Versions of man 1.5l and below contain a format string vulnerability. The
vulnerability occurs when man uses an optional catalog file, supplied by
the NLSPATH/LANG environmental variables. See the full
advisory for more 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.
Potentially exploitable buffer overflows exist in the Macromedia Flash
Player. The full advisory is here.
"The cumulative security patch is available today and addresses the
potential for exploits surrounding buffer overflows (read/write) and
sandbox integrity within the player, which might allow malicious users to
gain access to a user's computer. The possibility of running native code on
a users machine is a theoretical exploit, and extremely difficult to
execute in practice. There are no known examples of running such native
code from Macromedia Flash movies; however, even though this issue is
difficult and theoretical in nature only, we are encouraging users to
upgrade."
Jakob Lell discovered a bug in the 'noroff' script included in noweb
whereby a temporary file was created insecurely. During a review,
several other instances of this problem were found and fixed. Any of
these bugs could be exploited by a local user to overwrite arbitrary
files owned by the user invoking the script.
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."
The pam_xauth module is used to forward xauth information from user to user
in applications such as 'su'.
Andreas Beck discovered that versions of pam_xauth supplied with Red Hat
Linux since version 7.1 would forward authorization information from the
root account to unprivileged users. This could be used by a local attacker
to gain access to an administrator's X session. In order to exploit this
vulnerability, the attacker would have to get the administrator, as root,
to use su to the account belonging to the attacker.
Two vulnerabilities exists in the mail() PHP function. The first one allows
the execution of any program/script bypassing safe_mode restriction, the
second one may give an open-relay script if the mail() function is not
carefully used in PHP scripts. See this Bugtraq
report for more details. Note that this is a different vulnerability than the previous PHP mail() problem, which affected versions through 4.1.0.
A new set of buffer overflows has been discovered in PostgreSQL 7.2.2; they affect the circle_poly(), path_encode(), and path_addr() functions. Exploiting these overflows requires that the attacker first obtain a connection to the PostgreSQL server.
Zack Weinberg discovered that
os._execvpe from os.py uses a predictable name which could lead
to execution of arbitrary code. According to the Debian
advisory, the problem
was present in Python versions 1.5, 2.1 and 2.2.
The package radiusd-cistron is an implementation of the RADIUS protocol.
Unfortunately the RADIUS server handles large NAS numbers incorrectly. This
leads to overwriting internal memory of the server process and may be
abused to gain remote access to the system the RADIUS server is running on.
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.
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.
A problem has been discovered in the typespeed, a game that lets you
measure your typematic speed. By overflowing a buffer a local
attacker could execute arbitrary commands under the group id games.
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.
From the ISS
advisory:
"Vixie Cron is a scheduling daemon that ships with several Linux
distributions. Vixie Cron version 3.0pl1 could allow a local attacker to
gain root privileges. Crontab fails to properly drop privileges in certain
cases after a crontab modification operation. A local attacker could
exploit this vulnerability to gain root privileges on the system since
crontab is installed setuid root."
Note: this vulnerability is dated May 07 2001, and was first mentioned in
LWN on the May 10,
2001 security page.
miniserv.pl in the webmin package does not properly handle
metacharacters, such as line feeds and carriage returns, in
Base64-encoded strings used in Basic authentication. This
vulnerability allows remote attackers to spoof a session ID, and
thereby gain root privileges.
Versions of wget prior to 1.8.2-4 contain a bug that permits a malicious
FTP server to create or overwrite files anywhere on the local file system.
FTP clients must check to see if an FTP server's response to the NLST
command includes any directory information along with the list of filenames
required by the FTP protocol (RFC 959, section 4.1.3).
If the FTP client fails to do so, a malicious FTP server can send filenames
beginning with '/' or containing '/../' which can be used to direct a
vulnerable FTP client to write files (such as .forward, .rhosts, .shosts,
etc.) that can then be used for later attacks against the client machine.
The wwwoffle web proxy incorrectly processes HTTP PUT and POST requests
with negative Content Length values.
"It is believed
that an attacker could exploit this bug to gain remote wwwrun access
to the system wwwoffled is running on."
Xinetd is a 'master server' that is used to to accept service connection
requests and start the appropriate servers.
Because of a programming error, memory was allocated and never freed if a
connection was refused for any reason. An attacker could exploit this flaw
to crash the xinetd server, rendering all services it controls unavailable.
In addition, other flaws in xinetd could cause incorrect operation in
certain unusual server configurations.
All users of xinetd are advised to update to xinetd-2.3.11 which is not
vulnerable to these issues.
Xpdf suffers from the same sort of "execute arbitrary code embedded in a malicious document" vulnerability that is so widespread in other PostScript and PDF interpreters.
Joichi Ito has, with many helpers, compiled a report on privacy and
privacy-enhancing technologies which is intended to help with the
planning of electronic government initiatives in Japan. It's a large
thing, being several hundred pages available in PDF format. It is well
worth a look, though, as a comprehensive summary of the privacy situation
in several parts of the world.
The 12th Usenix Security Symposium is scheduled for August 4 through 8 in Washington, DC. Participants include Steve Bellovin, Bill Cheswick,
Niels Provos, Kevin Fu, Peter Gutmann, Dan Boneh, David Farber and Mark
Seiden. Registration is open now for interested participants.
The Tenth ACM Conference on Computer and Communications Security is happening in Washington, DC, on October 28 and 29. This year there will be a special session on "industrial experience in security." "This special session in an otherwise academic
conference is an opportunity for security practitioners in industry to
tell academics how it's really done: what works, and what doesn't.
Submissions are only 3 pages long, and so should impose minimal burden
on those submitting a paper." Papers are due June 27 (soon!).
