Re: LDAPv3 with simple authentication

[FOULDE Damien <damien.foulde () axians com>]

Hello,


You’ll find a packet capture attached to this email.

It would be really great if the signature provided previously could be reviewed.

 

Thank you & regards,


Damien

 

De : FOULDE Damien [mailto:damien.foulde () axians com] 
Envoyé : jeudi 29 décembre 2016 16:37
À : snort-sigs () lists sourceforge net
Objet : Re: [Snort-sigs] LDAPv3 with simple authentication

 

Hello,

 

The previous message is currently waiting for a moderator approval.

As it’s not released for the moment, I registered to the maillinglist and here it is.

 

Regards,

 

Damien

 

De : FOULDE Damien 
Envoyé : mercredi 21 décembre 2016 10:51
À : snort-sigs () lists sourceforge net
Objet : RE: LDAPv3 with simple authentication

 

Hello,

 

Any ideas / suggestions / advices will be greatly appreciated regarding this question.

 

In the meantime, here’s a working signature without fully decoding the BER data :

alert tcp any any -> any 389 (sid:1000000; gid:1; flow:established,to_server; content:"|30|"; depth:1; content:"|02|"; 
distance:1; within:127; content:"|60|"; distance:1; within:5; content:"|02 01 03 04|"; fast_pattern; distance:1; 
within:127; content:"|80|"; distance:1; within:127; content:!"|02 01 03 04 00 a3|"; offset:7; depth:257; msg:"LDAPv3 
simple Authentication"; classtype:policy-violation; rev:1; )

 

It would be great if it could be reviewed by Talos.

I can provide a packet capture if needed.

 

Regards,

 

Damien

 

De : FOULDE Damien [mailto:damien.foulde () axians com] 
Envoyé : lundi 19 décembre 2016 12:39
À : snort-sigs () lists sourceforge net
Objet : [Snort-sigs] LDAPv3 with simple authentication

 

Hello,

 

We need to write a signature to match on LDAPv3 with simple authentication.

LDAPv3 is described in the RFC 2251 through Abstract Syntax Notation 1 (ASN.1) and encoded through a subset of Basic 
Encoding Rules (BER) in the packets.

You may have a look to this great website http://www.selfadsi.org/ldap.htm#Frame to have a quick look over the encoding.

https://en.wikipedia.org/wiki/X.690#BER_encoding is also a good source of information.

As you should have seen the length can be encoded in a short or long form.

When the short form is used the MSB is set to 0 and the 7 remaining bits are used to encode the length directly from 0 
to 127.

Using the byte_jump function we should be able to jump to the next encoded data.

When the long form is used the MSB is set to 1 and the 7 remaining bits are used to encode the number of bytes that 
follow from 1 to 126 which will contains the actual length.

Using byte_extract and byte_jump functions with bitmask we should be able to jump to the next encoded data.

Before reaching the point where the LDAPv3 authentication is set to simple (encoded to 0) or sasl (encoded to 3) 
there’re 5 short or long length bytes.

Is there a way through the subset of snort packet dissection functions to match on this without writing 32 (2^5) 
different signatures to match all short / long possibilities ?

The BER encoding is also used to encode SNMP, the same kind of issue may have been seen there also.

 

Thank you for your help,

 

Damien

Attachment: LDAP_simple.pcap
Description:

Attachment: smime.p7s
Description:

------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most 
engaging tech sites, SlashDot.org! http://sdm.link/slashdot

_______________________________________________
Snort-sigs mailing list
Snort-sigs () lists sourceforge net
https://lists.sourceforge.net/lists/listinfo/snort-sigs

http://www.snort.org

Please visit http://blog.snort.org for the latest news about Snort!

Visit the Snort.org to subscribe to the official Snort ruleset, make sure to stay up to date to catch the most <a 
href=" https://snort.org/downloads/#rule-downloads";>emerging threats</a>!