On Fri, May 16, 2014 at 1:12 AM, Richard Sharpe
<realrichardsharpe@xxxxxxxxx> wrote:
> Hi folks,
>
> Simo Sorce informed me that there are some other SPNEGO sequences that
> Wireshark does not deal with. They turned up in some HTTP traffic.
>
> So, I decided to look at the issue of fixing the problem I am already
> aware of (it's in bugzilla somewhere.)
>
> This problem is that [MS-SPNG].pdf defines an negTokenInit2:
>
> NegHints ::= SEQUENCE {
> hintName[0] GeneralString OPTIONAL,
> hintAddress[1] OCTET STRING OPTIONAL
> }
> NegTokenInit2 ::= SEQUENCE {
> mechTypes[0] MechTypeList OPTIONAL,
> reqFlags [1] ContextFlags OPTIONAL,
> mechToken [2] OCTET STRING OPTIONAL,
> negHints [3] NegHints OPTIONAL,
> mechListMIC [4] OCTET STRING OPTIONAL,
> ...
> }
>
> and they coyly say:
>
> "Note In the ASN.1 description in the preceding, the NegTokenInit2
> message occupies the same context-specific ([X690] section 8.1.2.2)
> message ID (0) as does NegTokenInit in SPNEGO. "
>
> They also pointed out that hintAddress is never actually used.
>
> Now, these are only emitted by the server in a NegotiateResponse.
>
> I notice that the spnego.cnf file says this:
>
> #.FN_BODY NegTokenInit/mechListMIC
>
> gint8 ber_class;
> gboolean pc;
> gint32 tag;
> tvbuff_t *mechListMIC_tvb;
>
> /*
> * There seems to be two different forms this can take,
> * one as an octet string, and one as a general string in a
> * sequence.
> *
> * Peek at the header, and then decide which it is we're seeing.
> */
> get_ber_identifier(tvb, offset, &ber_class, &pc, &tag);
> if (ber_class == BER_CLASS_UNI && pc && tag == BER_UNI_TAG_SEQUENCE) {
> /*
> * It's a sequence.
> */
> return dissect_spnego_PrincipalSeq(FALSE, tvb, offset, actx, tree,
> hf_spnego_mechListMIC);
> } else {
>
> ...
> }
>
> So, the problem is that we have to dissect as if it is a netTokenInit2
> if we are in the appropriate context, otherwise as a negTokenInit, and
> the above stuff is one giant hack.
>
> Does anyone have any suggestions on how we can massage the .cnf file
> to determine this?
>
> I also have to get some captures showing these new SPNEGO things
> before making any changes.
The problems with SPNEGO dissection in HTTP requests and responses
seems to be related to mishandling the mechListMIC.
Here are the changes I think are needed for the ASN1 defn:
diff --git a/asn1/spnego/spnego.asn b/asn1/spnego/spnego.asn
index 190b3f1..1f1dcf7 100644
--- a/asn1/spnego/spnego.asn
+++ b/asn1/spnego/spnego.asn
@@ -24,10 +24,6 @@ MechTypeList ::= SEQUENCE OF MechType
-- to some flavor of "embrace, extend, expectorate" sequence from
-- Microsoft.
--
-PrincipalSeq ::= SEQUENCE {
- principal [0] GeneralString
-}
-
NegTokenInit ::= SEQUENCE {
mechTypes [0] MechTypeList OPTIONAL,
reqFlags [1] ContextFlags OPTIONAL,
@@ -35,6 +31,19 @@ NegTokenInit ::= SEQUENCE {
mechListMIC [3] OCTET STRING OPTIONAL
}
+NegHints ::= SEQUENCE {
+ hintName [0] GeneralString OPTIONAL,
+ hintAddress [1] OCTET STRING OPTIONAL
+}
+
+NegTokenInit2 ::= SEQUENCE {
+ mechTypes [0] MechTypeList OPTIONAL,
+ reqFlags [1] ContextFlags OPTIONAL,
+ mechToken [2] OCTET STRING OPTIONAL,
+ negHints [3] NegHints OPTIONAL,
+ mechListMIC [4] OCTET STRING OPTIONAL
+}
+
ContextFlags ::= BIT STRING {
delegFlag (0),
mutualFlag (1),
----------------------------------------------------
Then, I think what I have to do is to replace the current #.FN_XXXX
NegTokenInit* entries with one simply for NegTokenInit that looks at
whether we are dealing with a request or a response, and if a request,
uses negTokenInit else uses negTokenInit2.
Not sure how to do this at the moment, though.
Can anyone provide a hint?
--
Regards,
Richard Sharpe
(何以解憂？唯有杜康。--曹操)