Good point about IPv6. Looks like we could still do this using the same #
of SecRules and just not using an IP regex like this -
SecRule REQUEST_HEADERS:User-Agent "^(.*)$"
"phase:1,t:none,pass,nolog,t:sha1,t:hexEncode,setvar:tx.ua_hash=%{matched_v
ar}"
SecRule REQUEST_HEADERS:x-forwarded-for "^(.*?),?.*$"
"phase:1,t:none,pass,nolog,setvar:tx.real_ip=%{matched_var}"
SecRule &TX:REAL_IP "@eq 0"
"phase:1,t:none,pass,nolog,initcol:global=global,initcol:ip=%{remote_addr}_
%{tx.ua_hash},,setvar:tx.real_ip=%{remote_addr}"
SecRule &TX:REAL_IP "!@eq 0"
"phase:1,t:none,pass,nolog,initcol:global=global,initcol:ip=%{tx.real_ip}_%
{tx.ua_hash}"
--
Ryan
On 5/6/11 1:16 PM, "Oleg Gryb" <[email protected]> wrote:
>Ryan,
>
>Thanks for the update. It might have problems with IPv6 though. Here are
>my rules: they search for ',' and disregard the IP structure:
>
>
>SecRule REQUEST_HEADERS:User-Agent "^(.*)$"
>"phase:1,t:none,pass,nolog,t:sha1,t:hexEncode,setvar:tx.ua_hash=%{matched_
>var}"
>SecRule REQUEST_HEADERS:x-forwarded-for "^(.*)$"
>"phase:1,t:none,pass,nolog,setvar:tx.real_ip=%{matched_var}"
>SecRule TX:REAL_IP "^(.*?),.*$"
>"phase:1,t:none,pass,nolog,capture,setvar:tx.real_ip=%{TX.1}"
>
>SecRule &TX:REAL_IP "@eq 0"
>"phase:1,t:none,pass,nolog,initcol:global=global,initcol:ip=%{remote_addr}
>_%{tx.ua_hash},,setvar:tx.real_ip=%{remote_addr}"
>SecRule &TX:REAL_IP "!@eq 0"
>"phase:1,t:none,pass,nolog,initcol:global=global,initcol:ip=%{tx.real_ip}_
>%{tx.ua_hash}"
>
>Thanks,
>Oleg.
>
>--- On Thu, 5/5/11, Ryan Barnett <[email protected]> wrote:
>
>> From: Ryan Barnett <[email protected]>
>> Subject: Re: [Mod-security-developers] CRS DoS protection &
>>x-forwarded-for header
>> To: "Oleg Gryb" <[email protected]>,
>>"[email protected]"
>><[email protected]>
>> Cc: "[email protected]"
>><[email protected]>
>> Date: Thursday, May 5, 2011, 10:46 AM
>> FYI - updated the CRS 10 config file
>> to add in this logic and uploaded it to SVN -
>>
>>http://mod-security.svn.sourceforge.net/viewvc/mod-security/crs/trunk/mod
>>security_crs_10_config.conf.example?revision=1772
>>
>> #
>> # -=[ Global and IP Collections ]=-
>> #
>> # Create both Global and IP collections for rules to use
>> # There are some CRS rules that assume that these two
>> collections
>> # have already been initiated.
>> #
>> SecRule REQUEST_HEADERS:User-Agent "^(.*)$"
>>
>>"phase:1,id:'981217',t:none,pass,nolog,t:sha1,t:hexEncode,setvar:tx.ua_ha
>>sh=%{matched_var}"
>> SecRule REQUEST_HEADERS:x-forwarded-for
>> "^\b(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\b"
>>
>>"phase:1,id:'981225',t:none,pass,nolog,capture,setvar:tx.real_ip=%{tx.1}"
>> SecRule &TX:REAL_IP "!@eq 0"
>>
>>"phase:1,id:'981226',t:none,pass,nolog,initcol:global=global,initcol:ip=%
>>{tx.real_ip}_%{tx.ua_hash}"
>> SecRule &TX:REAL_IP "@eq 0"
>>
>>"phase:1,id:'981218',t:none,pass,nolog,initcol:global=global,initcol:ip=%
>>{remote_addr}_%{tx.ua_hash}"
>>
>> The new rules will grab the first IP address listed in an
>> X-Forwared-For header and use that for the IP collection
>> key. If X-Forwarded-For is not present, then it will
>> use REMOTE_ADDR.
>>
>> Thanks for the suggestion!
>>
>> -Ryan
>>
>>
>> On 4/28/11 8:19 PM, "Oleg Gryb"
>><[email protected]<mailto:[email protected]>>
>> wrote:
>>
>> I've just realized that there might be a problem with
>> relying on that header: if
>> an attacker intentionally sends different random IPs in
>> there, DoS protection
>> can be efficiently by-passed. In my case it should not
>> happen, because an LB is
>> the one who adds the header, but in general we should warn
>> engineers about the
>> possible exploit.
>>
>>
>> Actually, even in LB case: if a request has already had the
>> header, LB will
>> create a new one with the existing value appended to the
>> client IP:
>>
>> x-forwarded-for: real-client-ip,
>> whatever-client-sent-to-LB
>>
>> It means that we would need to rely on the the first IP in
>> the list, everything
>> else should be considered as untrusted.
>>
>> Thanks,
>> Oleg.
>>
>>
>> ----- Original Message ----
>> From: Ryan Barnett
>><[email protected]<mailto:[email protected]>>
>> To: Oleg Gryb <[email protected]<mailto:[email protected]>>;
>>
>>"[email protected]<mailto:mod-security-develo
>>[email protected]>"
>>
>><[email protected]<mailto:mod-security-develo
>>[email protected]>>
>> Cc:
>>"[email protected]<mailto:owasp-modsecurity
>>[email protected]>"
>>
>><[email protected]<mailto:owasp-modsecurity
>>[email protected]>>
>> Sent: Thu, April 28, 2011 4:41:14 PM
>> Subject: Re: [Mod-security-developers] CRS DoS protection
>> & x-forwarded-for
>> header
>> Thanks for the updates Oleg! This will certainly be a
>> useful update to
>> not only the DoS rules buy any rules that will be based on
>> the client IP.
>> I will actually go back to check other uses of REMOTE_ADDR
>> and see if we
>> can swap it for tx.real_ip instead.
>> I will add this to the CRS v2.2.0 that I am working
>> on.
>> For future reference - here is the OWASP CRS
>> mail-list -
>> https://lists.owasp.org/mailman/listinfo/owasp-modsecurity-core-rule-set
>> --
>> Ryan Barnett
>> Senior Security Researcher
>> Trustwave - SpiderLabs
>> On 4/28/11 7:32 PM, "Oleg Gryb"
>><[email protected]<mailto:[email protected]>>
>> wrote:
>> >I'm not sure if I can discuss CRS rules here. If not,
>> please let me know
>> >what
>> >the right place is. I want to suggest an
>> improvement to DoS protection in
>> >CRS
>> >2.1.2. The problem is that enterprise
>> applications usually run behind
>> >load
>> >balancers, so relying on remote_addr doesn't make
>> too much sense, because
>> >you'll
>> >always have an LB's IP in there.
>> >
>> >
>> >My improved rules (attached) check for
>> x-forwarded-for header and if
>> >it's
>> >present, this IP will be used to initialize IP
>> collection. If it's not
>> >then the
>> >old logic will be used.
>> >
>> >It would be great if we can include this
>> improvement to the next CRS
>> >release.
>> >
>> >Thanks,
>> >Oleg.
>>
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