[Emerging-Sigs] Bash 0-day

Jake Warren jake.warren at masergy.com
Wed Sep 24 19:58:39 EDT 2014


Taking a stab at some rules for detecting malicious DHCP packets. Haven't
been able to test these though. I haven't seen anybody post a PoC for
injection via DHCP yet.

//option 15 - domain name
alert udp any 67 -> any 68 (msg:"Possible CVE-2014-6271 exploit attempt via
malicious DHCP ACK - option 15"; content:"|02 01|"; depth:2;
content:"|0f|"; distance:238; content:"|28 29 20 7b 20|"; distance:1;
within:10; classtype:misc-attack; reference:url,
access.redhat.com/articles/1200223; reference:cve,2014-6271; sid:xxxx;
rev:1;)

//option 67 - filename
alert udp any 67 -> any 68 (msg:"Possible CVE-2014-6271 exploit attempt via
malicious DHCP ACK - option 67"; content:"|02 01|"; depth:2;
content:"|43|"; distance:238; content:"|28 29 20 7b 20|"; distance:1;
within:10; classtype:misc-attack; reference:url,
access.redhat.com/articles/1200223; reference:cve,2014-6271; sid:xxxx;
rev:1;)

Reference Link:
https://www.reddit.com/r/netsec/comments/2hbxtc/cve20146271_remote_code_execution_through_bash/ckrh029

-Jake Warren


On Wed, Sep 24, 2014 at 5:07 PM, Will Metcalf <
wmetcalf at emergingthreatspro.com> wrote:

> 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
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>>>> =VV4h
>>>> -----END PGP SIGNATURE-----
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>>>
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>>
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>
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