Draft announcement:
---------------------------------------------------------------------
fetchmail-SA-2008-01: Crash on large log messages in verbose mode
Topics: Crash in large log messages in verbose mode.
Author: Matthias Andree
Version: 1.0
Announced:
Type: Dereferencing garbage pointer trigged by outside circumstances
Impact: denial of service possible
Danger: low
CVSS V2 vector: (AV:N/AC:M/Au:N/C:N/I:N/A:C/E:P/RL:O/RC:C)
Credits: Petr Uzel (fix), Petr Cerny (analysis), Gunter Nau (bug report)
CVE Name: XXX
URL: http://www.fetchmail.info/fetchmail-SA-2008-01.txt
Project URL: http://www.fetchmail.info/
Affects: fetchmail release < 6.3.9 exclusively
Not affected: fetchmail release 6.3.9 and newer
systems without varargs (stdargs.h) support.
Corrected: 2008-06-13 fetchmail SVN (rev XXX)
0. Release history
==================
2008-06-13 1.0 first draft for MITRE/CVE (visible in SVN)
1. Background
=============
fetchmail is a software package to retrieve mail from remote POP2, POP3,
IMAP, ETRN or ODMR servers and forward it to local SMTP, LMTP servers or
message delivery agents.
fetchmail ships with a graphical, Python/Tkinter based configuration
utility named "fetchmailconf" to help the user create configuration (run
control) files for fetchmail.
2. Problem description and Impact
=================================
Gunter Nau reported fetchmail crashing on some messages; further
debugging by Petr Uzel and Petr Cerny at Novell/SUSE Czech Republic
dug up that this happened when fetchmail was trying to print, in -v -v
verbose level, headers exceeding 2048 bytes. In this situation,
fetchmail would resize the buffer and fill in further parts of the
message, but forget to reinitialize its va_list typed source pointer,
thus reading data from a garbage address found on the stack at
addresses above the function arguments the caller passed in; usually
that would be the caller's stack frame.
It is unknown whether code can be injected remotely, but given that
the segmentation fault is caused by read accesses, the relevant data
is not under the remote attacker's control and no buffer overrun
situation is present that would allow altering program /flow/, it is
deemed rather unlikely that code can be injected.
Note that the required -vv configuration at hand is both non-default
and also not common in automated (cron job) setups, but usually used
in manual debugging, so not many systems would be affected by the
problem. Nonetheless, in vulnerable configurations, it is remotely
exploitable to effect a denial of service attack.
3. Solution
===========
There are two alternatives, either of them by itself is sufficient:
a. Apply the patch found in section B of this announcement to
fetchmail 6.3.8, recompile and reinstall it.
b. Install fetchmail 6.3.9 or newer when it becomes available. The
fetchmail source code is available from
<http://developer.berlios.de/project/showfiles.php?group_id=1824>.
4. Workaround
=============
Run fetchmail at low verbosity, avoid using two or three -v arguments;
internal messages are short and do not contain external message
sources so they do not cause buffer resizing. It is recommended to
replace the vulnerable code by a fixed version (see previous
section 3. Solution) as soon as reasonably possible.
A. Copyright, License and Warranty
==================================
(C) Copyright 2008 by Matthias Andree, <matthias.andree@gmx.de>.
Some rights reserved.
This work is licensed under the Creative Commons
Attribution-NonCommercial-NoDerivs German License. To view a copy of
this license, visit http://creativecommons.org/licenses/by-nc-nd/2.0/de/
or send a letter to Creative Commons; 559 Nathan Abbott Way;
Stanford, California 94305; USA.
THIS WORK IS PROVIDED FREE OF CHARGE AND WITHOUT ANY WARRANTIES.
Use the information herein at your own risk.
B. Patch to remedy the problem
==============================
diff --git a/report.c b/report.c
index 31d4e48..2a731ac 100644
--- a/report.c
+++ b/report.c
@@ -238,11 +238,17 @@ report_build (FILE *errfp, message, va_alist)
rep_ensuresize();
#if defined(VA_START)
- VA_START (args, message);
for ( ; ; )
{
+ /*
+ * args has to be initialized before every call of vsnprintf(),
+ * because vsnprintf() invokes va_arg macro and thus args is
+ * undefined after the call.
+ */
+ VA_START(args, message);
n = vsnprintf (partial_message + partial_message_size_used,
partial_message_size - partial_message_size_used,
message, args);
+ va_end (args);
if (n >= 0
&& (unsigned)n < partial_message_size - partial_message_size_used)
@@ -254,7 +260,6 @@ report_build (FILE *errfp, message, va_alist)
partial_message_size += 2048;
partial_message = REALLOC (partial_message, partial_message_size);
}
- va_end (args);
#else
for ( ; ; )
{
END OF fetchmail-SA-2008-01.txt
------------------------------------------------------------------------------------------
++++amd64++++
1. Compiles.
2. Installs correctly.
3. Merges.
4. Killing fetchmail and restarting it results in the bugspam keeping on
coming
in ;-)
5. Starting in verbose mode and sending myself a large message does not
result
in a crash.
Portage 2.1.4.4 (default-linux/amd64/2007.0, gcc-4.1.2, glibc-2.6.1-r0,
2.6.24-gentoo-r8 x86_64)
=================================================================
System uname: 2.6.24-gentoo-r8 x86_64 AMD Athlon(tm) 64 Processor 3400+
Timestamp of tree: Sun, 15 Jun 2008 12:00:01 +0000
ccache version 2.4 [enabled]
app-shells/bash: 3.2_p33
dev-lang/python: 2.4.4-r13
dev-python/pycrypto: 2.0.1-r6
dev-util/ccache: 2.4-r7
sys-apps/baselayout: 1.12.11.1
sys-apps/sandbox: 1.2.18.1-r2
sys-devel/autoconf: 2.13, 2.61-r1
sys-devel/automake: 1.5, 1.7.9-r1, 1.8.5-r3, 1.9.6-r2, 1.10.1
sys-devel/binutils: 2.18-r1
sys-devel/gcc-config: 1.4.0-r4
sys-devel/libtool: 1.5.26
virtual/os-headers: 2.6.23-r3
ACCEPT_KEYWORDS="amd64"
CBUILD="x86_64-pc-linux-gnu"
CFLAGS="-march=athlon64 -O2 -pipe"
CHOST="x86_64-pc-linux-gnu"
CONFIG_PROTECT="/etc /usr/kde/3.5/env /usr/kde/3.5/share/config
/usr/kde/3.5/shutdown /usr/kde/svn/env /usr/kde/svn/share/config
/usr/kde/svn/shutdown /usr/share/config"
CONFIG_PROTECT_MASK="/etc/env.d /etc/fonts/fonts.conf /etc/gconf
/etc/gentoo-release /etc/revdep-rebuild /etc/terminfo /etc/texmf/web2c
/etc/udev/rules.d"
CXXFLAGS="-march=athlon64 -O2 -pipe"
DISTDIR="/distfiles"
FEATURES="ccache collision-protect distlocks metadata-transfer
multilib-strict
parallel-fetch sandbox sfperms strict test unmerge-orphans userfetch
userpriv"
GENTOO_MIRRORS="http://distfiles.gentoo.org
http://distro.ibiblio.org/pub/linux/distributions/gentoo"
MAKEOPTS="-j2"
PKGDIR="/usr/portage/packages"
PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times
--compress
--force --whole-file --delete --stats --timeout=180 --exclude=/distfiles
--exclude=/local --exclude=/packages"
PORTAGE_TMPDIR="/var/tmp"
PORTDIR="/usr/portage"
PORTDIR_OVERLAY="/usr/portage/local/layman/science /overlay"
SYNC="rsync://raptor.gentoo.osuosl.org/gentoo-portage"
USE="X acl aiglx aim amd64 berkdb branding cli cracklib crypt cups dri
fortran
gdbm gpm gtk iconv imap ipv6 isdnlog midi mmx mpeg3 mudflap ncurses nls
nptl
nptlonly nvidia opengl openmp pam pcre perl pppd python qt3 readline
reflection
session sockets spl sqlite3 sse sse2 ssl tcpd unicode vim xcomposite xine
xorg
zlib" ALSA_CARDS="ali5451 als4000 atiixp atiixp-modem bt87x ca0106 cmipci
emu10k1x ens1370 ens1371 es1938 es1968 fm801 hda-intel intel8x0 intel8x0m
maestro3 trident usb-audio via82xx via82xx-modem ymfpci"
ALSA_PCM_PLUGINS="adpcm alaw asym copy dmix dshare dsnoop empty extplug
file
hooks iec958 ioplug ladspa lfloat linear meter mulaw multi null plug rate
route
share shm softvol" APACHE2_MODULES="actions alias auth_basic authn_alias
authn_anon authn_dbm authn_default authn_file authz_dbm authz_default
authz_groupfile authz_host authz_owner authz_user autoindex cache dav
dav_fs
dav_lock deflate dir disk_cache env expires ext_filter file_cache filter
headers include info log_config logio mem_cache mime mime_magic negotiation
rewrite setenvif speling status unique_id userdir usertrack vhost_alias"
ELIBC="glibc" INPUT_DEVICES="keyboard mouse evdev" KERNEL="linux"
LCD_DEVICES="bayrad cfontz cfontz633 glk hd44780 lb216 lcdm001 mtxorb
ncurses
text" USERLAND="GNU" VIDEO_CARDS="nvidia"
Unset: CPPFLAGS, CTARGET, EMERGE_DEFAULT_OPTS, INSTALL_MASK, LANG, LC_ALL,
LDFLAGS, LINGUAS, PORTAGE_COMPRESS, PORTAGE_COMPRESS_FLAGS,
PORTAGE_RSYNC_EXTRA_OPTS
