[Bro] Digging through Source Code

Weasel, Gary W Jr CIV DISA RE (US) gary.w.weasel2.civ at mail.mil
Tue Jun 20 13:42:35 PDT 2017

Yes, but there's something that's still stumping me.

Looking at line 70 from https://github.com/bro/bro/blob/master/src/analyzer/protocol/krb/krb-analyzer.pac

case 8:
        if ( element->data()->etype()->data()->size() )
                rv->Assign(11, proc_cipher_list(element->data()->etype()));

Following the breadcrumb trail in the if statement here...

        element is type KRB_REQ_Arg (defined - https://github.com/bro/bro/blob/master/src/analyzer/protocol/krb/krb-protocol.pac)
->      data is type KRB_REQ_Arg_Data (defined - https://github.com/bro/bro/blob/master/src/analyzer/protocol/krb/krb-protocol.pac)
->      etype is type Array (defined - https://github.com/bro/bro/blob/master/src/analyzer/protocol/asn1/asn1.pac)
->      data is type ASN1Encoding (defined - https://github.com/bro/bro/blob/master/src/analyzer/protocol/asn1/asn1.pac)
->      size is type ?

Following this line of thought, I'm a little confused by what "size()" is supposed to mean here, since it's not an attribute.  I can infer that it's simply returning the size of the record, but I don't have any information as to how or where that would be defined.  I've also tried looking through the source of BinPAC (https://www.bro.org/sphinx/components/binpac/README.html) but have come up empty so far.

I have a sample of kerberos pcap that populates the msg$pa_data$encryption_type vector (from event krb_tgs_request), so I know that the aforementioned if statement is returning true - - but the other two vectors "host_addrs" and "additional"tickets" (that from documentation seem to imply they're parallel with the encryption_type vector) come up as <uninitialized>.

This made me question that maybe there was something wrong with the code that was causing it to miss the host_addr and ticket data, I clearly find this data in my pcap sample under padata.  This is my current theory anyway, and wanted to see if I'm making a bad assumption somewhere or if someone can shed light on what's going on here.

-----Original Message-----
From: Azoff, Justin S [mailto:jazoff at illinois.edu]
Sent: Tuesday, June 20, 2017 3:28 PM
To: Weasel, Gary W Jr CIV DISA RE (US) <gary.w.weasel2.civ at mail.mil>
Cc: bro at bro.org
Subject: Re: [Bro] Digging through Source Code

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> On Jun 20, 2017, at 3:14 PM, Weasel, Gary W Jr CIV DISA RE (US) <gary.w.weasel2.civ at mail.mil> wrote:
> All,
> I've been digging through the Bro source code, and there's been something that's mystifying me for a while now.
> type Array = record {
>        array_meta: ASN1EncodingMeta;
>        data:       ASN1Encoding[];
> };
> As from https://github.com/bro/bro/blob/57da2d091b30aad52d52fce8018feeb2cdf8ff1f/src/analyzer/protocol/asn1/asn1.pac
> I have no clue what "record" is in this context.  I suspect it has other attributes that are being inherited, but I haven't found anything to indicate what this is.  Does anyone have any insight into this?
> Thanks,
> - Gary

Does this help?


- Justin Azoff

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