[Emerging-Sigs] Bash 0-day

Markus Manzke mm at mare-system.de
Wed Sep 24 18:58:19 EDT 2014


as far as i can see this will work against the POC
curl -k -H 'User-Agent: () { :;}; echo aa>/tmp/aa'  https://localhost/cgi-bin/hi
like here
http://www.reddit.com/r/netsec/comments/2hbxtc/cve20146271_remote_code_execution_through_bash/ckrbqac

but will fail when using (please note the additional spaces)
curl -k -H 'User-Agent: ()       { :;}; echo aa>/tmp/aa'  https://localhost/cgi-bin/hi
hai

i'd go, although this is heavy, with the following regex (esp. for the headers):
\(\).*{.*}.*;




On 09/25/2014 12:07 AM, Will Metcalf 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
> <http://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
> <http://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
> <http://blogs.akamai.com/2014/09/environment-bashing.html>;)
> 
> 
> On Wed, Sep 24, 2014 at 4:59 PM, Jake Warren <jake.warren at masergy.com <mailto: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
>     <mailto: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 <mailto:cnelson at ucsd.edu>>
>         wrote:
> 
> 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.
> 
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