[Emerging-Sigs] Bash 0-day

Will Metcalf wmetcalf at emergingthreatspro.com
Wed Sep 24 18:07:47 EDT 2014


We should have these rolled out shortly. went with the following. Regex is
to reduce FP's we had during testing.

alert tcp any any -> $HTTP_SERVERS $HTTP_PORTS (msg:"ET WEB_SERVER Possible
CVE-2014-6271 Attempt in URI"; flow:established,to_server; content:"|28 29
20 7b 20|"; http_uri; fast_pattern:only;
pcre:"/[=?&\x2f]\s*?\x28\x29\x20\x7b\x20/U"; sid:2019231; rev:1;
classtype:attempted-admin; reference:url,
blogs.akamai.com/2014/09/environment-bashing.html;)

alert tcp any any -> $HTTP_SERVERS $HTTP_PORTS (msg:"ET WEB_SERVER Possible
CVE-2014-6271 Attempt in Headers"; flow:established,to_server; content:"|28
29 20 7b 20|"; http_header; fast_pattern:only; sid:2019232; rev:1;
classtype:attempted-admin; reference:url,
blogs.akamai.com/2014/09/environment-bashing.html;)

alert tcp any any -> $HTTP_SERVERS $HTTP_PORTS (msg:"ET WEB_SERVER Possible
CVE-2014-6271 Attempt in Client Body"; flow:established,to_server;
content:"|28 29 20 7b 20|"; http_client_body; fast_pattern:only;
pcre:"/(?:^|[=?&])\s*?\x28\x29\x20\x7b\x20/P"; sid:2019233; rev:1;
classtype:attempted-admin; reference:url,
blogs.akamai.com/2014/09/environment-bashing.html;)


On Wed, Sep 24, 2014 at 4:59 PM, Jake Warren <jake.warren at masergy.com>
wrote:

> Here's my attempt at some rules for the cgi attack vector. Poorly written
> rules with horrible performance but they do at least catch the initial PoC
> attacks. :-)
>
> alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"Possible
> CVE-2014-6271 exploit attempt via HTTP headers"; content:"|28|";
> http_header; content:"|29|"; http_header; distance:0; within:10;
> content:"|7b|"; http_header; distance:0; within:10; content:"|3a|";
> http_header; distance:0; within:10; content:"|3b|"; http_header;
> distance:0; within:10; content:"|7d|"; http_header; fast_pattern;
> distance:0; within:10; content:"|3b|"; http_header; distance:0; within:10;
> classtype:web-application-attack; reference:cve,2014-6271; sid:xxxx; rev:1;)
>
> alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"Possible
> CVE-2014-6271 exploit attempt via HTTP URI"; content:"|28|"; http_uri;
> content:"|29|"; http_uri; distance:0; within:10; content:"|7b|"; http_uri;
> distance:0; within:10; content:"|3a|"; http_uri; distance:0; within:10;
> content:"|3b|"; http_uri; distance:0; within:10; content:"|7d|"; http_uri;
> fast_pattern; distance:0; within:10; content:"|3b|"; http_uri; distance:0;
> within:10; classtype:web-application-attack; reference:cve,2014-6271;
> sid:xxxx; rev:1;)
>
> -Jake Warren
>
>
> On Wed, Sep 24, 2014 at 12:54 PM, Darien Huss <dhuss at emergingthreats.net>
> wrote:
>
>> Thanks Cooper, we should have something going out today for this.
>>
>> Regards,
>> Darien
>>
>> On Wed, Sep 24, 2014 at 1:33 PM, Cooper F. Nelson <cnelson at ucsd.edu>
>> wrote:
>>
>>> -----BEGIN PGP SIGNED MESSAGE-----
>>> Hash: SHA1
>>>
>>> This popped up on one of my mailing lists today:
>>>
>>> >
>>> https://securityblog.redhat.com/2014/09/24/bash-specially-crafted-environment-variables-code-injection-attack/
>>>
>>> This is an example of the exploit code:
>>>
>>> > $ env x='() { :;}; echo vulnerable' bash -c "echo this is a test"
>>> >  vulnerable
>>> >  this is a test
>>>
>>> I'm not sure of what would be the best way to detect this, as its
>>> potentially exploitable via multiple ports/protocols and I suspect
>>> trivial to obfuscate.
>>>
>>> - --
>>> Cooper Nelson
>>> Network Security Analyst
>>> UCSD ACT Security Team
>>> cnelson at ucsd.edu x41042
>>> -----BEGIN PGP SIGNATURE-----
>>> Version: GnuPG v2.0.17 (MingW32)
>>>
>>> iQEcBAEBAgAGBQJUIwBXAAoJEKIFRYQsa8FW3+4H/3qMEZ5MirfKyd21/TyyWXgy
>>> BLiIlNojmmB/xG+vcgjI9efTY+i6+6gE4zPl0ID6EOU89m/oCEcghO9zw09arO3H
>>> YmFeJRZjpIK3iym+FGZMIDvo2F4tt76Oo+58wWxYqkNjYUKWVde6e18wp15hPx/L
>>> Uy1S1Ec3AozhEjNcFgUR6vI7hRz+bmEv5Qa2dLfsiEuWBkJvTw9wYnHYjFgrNMOm
>>> 3w6lyJmkOC2R+/A0CD436IbnEg55uSwL6kE0pdGfmx4b9kHpJ9Wauj3lLsUUo/PF
>>> ja0FhmeGhtfjzrSlJXw7mWUKXMujPviYZswzGZWyQknfktFwHLKplM+cz4LBaZQ=
>>> =VV4h
>>> -----END PGP SIGNATURE-----
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>>
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>
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