10 April, 2009

Upgrading to Snort 2.8.4

Hopefully, everyone running Snort has been paying attention and noticed that Snort 2.8.4 was released on 07 April and the corresponding new rule sets were released on 08 April. If you pay for Snort rules, the new netbios.rules will not work with Snort versions prior to 2.8.4, so you need to upgrade.

Upgrading was mostly painless just to get Snort running, though the dcerpc2 preprocessor settings definitely may require tweaking beyond the defaults. Generally, when I'm upgrading and there is something like a new preprocessor, I will start by getting Snort upgraded and successfully running with the defaults for the preprocessor, then will tune the settings as needed after I'm sure the new version is working.

The first thing to do after downloading and extracting is read the RELEASENOTES and also any applicable READMEs. Since the dcerpc2 preprocessor is new, the README.dcerpc2 may be of particular interest. A lot of people don't realize how much documentation is included.

$ wget http://www.snort.org/dl/snort-2.8.4.tar.gz
$ tar xzf snort-2.8.4.tar.gz
$ cd snort-2.8.4/doc
$ ls
BUGS README.asn1 README.sfportscan
Makefile.am README.dcerpc README.stream5
Makefile.in README.dcerpc2 README.tag
NEWS README.decode* README.thresholding
PROBLEMS README.decoder_preproc_rules README.variables
README.INLINE README.ftptelnet faq.pdf
README.PerfProfiling README.http_inspect generators
README.SMTP README.ipip snort_manual.pdf
README.UNSOCK README.ipv6 snort_manual.tex
README.WIN32 README.pcap_readmode snort_schema_v106.pdf
The following is the default configuration as listed in the README.dcerpc2.
preprocessor dcerpc2_server: default, policy WinXP, \
detect [smb [139,445], tcp 135, udp 135, rpc-over-http-server 593], \
autodetect [tcp 1025:, udp 1025:, rpc-over-http-server 1025:], \
smb_max_chain 3
For some environments, it may be useful to turn off the preprocessor alerts or turn them off for specific systems.
preprocessor dcerpc2: memcap 102400, events none
preprocessor dcerpc2_server: default, policy WinXP, \
detect [smb [139,445], tcp 135, udp 135, rpc-over-http-server 593], \
autodetect [tcp 1025:, udp 1025:, rpc-over-http-server 1025:], \
smb_max_chain 3
preprocessor dcerpc2_server: net $SCANNERS, detect none
No matter what, the dcerpc configuration should be removed from the snort.conf and replaced with a dcerpc2 configuration for Snort 2.8.4.

After that, I'll configure and install Snort.
$  ./configure --enable-dynamicplugin --enable-inline --enable-perfprofiling
$ make
$ sudo /etc/rc.d/rc.snort-inline stop
$ sudo make install
$ which snort
$ snort -V

,,_ -*> Snort! <*-
o" )~ Version 2.8.4 (Build 26) inline
'''' By Martin Roesch & The Snort Team: http://www.snort.org/team.html
Copyright (C) 1998-2009 Sourcefire, Inc., et al.
Using PCRE version: 7.7 2008-05-07

$ sudo /etc/rc.d/rc.snort-inline start
Starting snort-inline
Initializing Inline mode
building cached socket reset packets
Although the old netbios.rules will still work with the new version, it's also time to update to the latest rules to take advantage of the smaller number of netbios.rules. Note that this only applies for subscription rules since the free ones won't reflect the changes for 30 days.

Some of the rules in the new netbios.rules file have SIDs that were unchanged, so I decided to re-enable any of those that I had previously disabled in my oinkmaster.conf. I can always disable them again, but with the new preprocessor and possible changes to the remaining SIDs, I decided it was best to reevaluate them.

Since I'm also using precompiled shared object rules, I also update from the ones compiled for to the ones compiled for 2.8.4. I keep the rule stubs in a directory along with symlinks to the corresponding SO files, so I simply remove the symlink and recreate it to the new SO rules.
$ rm /etc/snort/so_rules/*so
$ ln -s /etc/snort/so_rules/precompiled/CentOS-5.0/i386/2.8.4/*so /etc/snort/so_rules/

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