Wireshark-bugs: [Wireshark-bugs] [Bug 9398] dissectors bug with a SASL/GSSAPI/Kerberos security
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From: bugzilla-daemon@xxxxxxxxxxxxx
Date: Fri, 30 May 2014 03:34:52 +0000

Comment # 4 on bug 9398 from 
OK, this looks like the problem in dissect_spnego_krb5_cfx_wrap_base:

static int
dissect_spnego_krb5_cfx_wrap_base(tvbuff_t *tvb, int offset, packet_info *pinfo
#ifndef HAVE_KERBEROS
        _U_
#endif
    , proto_tree *tree, guint16 token_id _U_
    )
{
        guint8 flags;
        guint16 ec;
#if defined(HAVE_HEIMDAL_KERBEROS) || defined(HAVE_MIT_KERBEROS)
        guint16 rrc;
#endif
        int checksum_size;
        int start_offset=offset;

        /*
         * The KRB5 blob conforms to RFC4121:
         *   USHORT (0x0504)
         *   and so on }
         */

        /* Now, the sign and seal algorithms ... */

        flags = tvb_get_guint8(tvb, offset);
        offset = dissect_spnego_krb5_cfx_flags(tvb, offset, tree, flags);

        pinfo->gssapi_data_encrypted=(flags & 2);

        /* Skip the filler */

        proto_tree_add_item(tree, hf_spnego_krb5_filler, tvb, offset, 1,
                            ENC_NA);
        offset += 1;

        /* EC */
        ec = tvb_get_ntohs(tvb, offset);
        proto_tree_add_item(tree, hf_spnego_krb5_cfx_ec, tvb, offset, 2,
                            ENC_BIG_ENDIAN);
        offset += 2;
        /* RRC */
#if defined(HAVE_HEIMDAL_KERBEROS) || defined(HAVE_MIT_KERBEROS)
        rrc = tvb_get_ntohs(tvb, offset);
#endif
        proto_tree_add_item(tree, hf_spnego_krb5_cfx_rrc, tvb, offset, 2,
                            ENC_BIG_ENDIAN);
        offset += 2;

        /* sequence number */

        proto_tree_add_item(tree, hf_spnego_krb5_cfx_seq, tvb, offset, 8,
                            ENC_BIG_ENDIAN);
        offset += 8;

        /* Checksum of plaintext padded data */

        if (pinfo->gssapi_data_encrypted) {
                checksum_size = 44 + ec;
        } else {
                checksum_size = 12;
        }

        proto_tree_add_item(tree, hf_spnego_krb5_sgn_cksum, tvb, offset,
                            checksum_size, ENC_NA);
        offset += checksum_size;

This last pair should only be done if pinfo->gssapi_data_encrypted is set,
otherwise we should defer adding this element until after the payload is
decrypted and then add the checksum as the last 12 bytes.

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