Commit message: CVE-2017-11103: Orpheus' Lyre KDC-REP service name validation

In _krb5_extract_ticket() the KDC-REP service name must be obtained from
encrypted version stored in 'enc_part' instead of the unencrypted version
stored in 'ticket'.  Use of the unecrypted version provides an
opportunity for successful server impersonation and other attacks.

Identified by Jeffrey Altman, Viktor Duchovni and Nico Williams.

Change-Id: I45ef61e8a46e0f6588d64b5bd572a24c7432547c
CVE: CVE-2017-11103
CWE: CWE-345
Vulnerability description: Heimdal before 7.4 allows remote attackers to impersonate services with Orpheus' Lyre attacks because it obtains service-principal names in a way that violates the Kerberos 5 protocol specification. In _krb5_extract_ticket() the KDC-REP service name must be obtained from the encrypted version stored in 'enc_part' instead of the unencrypted version stored in 'ticket'. Use of the unencrypted version provides an opportunity for successful server impersonation and other attacks. NOTE: this CVE is only for Heimdal and other products that embed Heimdal code; it does not apply to other instances in which this part of the Kerberos 5 protocol specification is violated.

Project: heimdal
File: ticket.c

_krb5_extract_ticket(krb5_context context,
		     krb5_kdc_rep *rep,
		     krb5_creds *creds,
		     krb5_keyblock *key,
		     krb5_const_pointer keyseed,
		     krb5_key_usage key_usage,
		     krb5_addresses *addrs,
		     unsigned nonce,
		     unsigned flags,
		     krb5_data *request,
		     krb5_decrypt_proc decrypt_proc,
		     krb5_const_pointer decryptarg)
{
    krb5_error_code ret;
    krb5_principal tmp_principal;
    size_t len = 0;
    time_t tmp_time;
    krb5_timestamp sec_now;

    /* decrypt */

    if (decrypt_proc == NULL)
	decrypt_proc = decrypt_tkt;

    ret = (*decrypt_proc)(context, key, key_usage, decryptarg, rep);
    if (ret)
	goto out;

    if (rep->enc_part.flags.enc_pa_rep && request) {
	krb5_crypto crypto = NULL;
	Checksum cksum;
	PA_DATA *pa = NULL;
	int idx = 0;

	_krb5_debug(context, 5, "processing enc-ap-rep");

	if (rep->enc_part.encrypted_pa_data == NULL ||
	    (pa = krb5_find_padata(rep->enc_part.encrypted_pa_data->val,
				   rep->enc_part.encrypted_pa_data->len,
				   KRB5_PADATA_REQ_ENC_PA_REP,
				   &idx)) == NULL)
	{
	    _krb5_debug(context, 5, "KRB5_PADATA_REQ_ENC_PA_REP missing");
	    ret = KRB5KRB_AP_ERR_MODIFIED;
	    goto out;
	}
	
	ret = krb5_crypto_init(context, key, 0, &crypto);
	if (ret)
	    goto out;
	
	ret = decode_Checksum(pa->padata_value.data,
			      pa->padata_value.length,
			      &cksum, NULL);
	if (ret) {
	    krb5_crypto_destroy(context, crypto);
	    goto out;
	}
	
	ret = krb5_verify_checksum(context, crypto,
				   KRB5_KU_AS_REQ,
				   request->data, request->length,
				   &cksum);
	krb5_crypto_destroy(context, crypto);
	free_Checksum(&cksum);
	_krb5_debug(context, 5, "enc-ap-rep: %svalid", (ret == 0) ? "" : "in");
	if (ret)
	    goto out;
    }

    /* save session key */

    creds->session.keyvalue.length = 0;
    creds->session.keyvalue.data   = NULL;
    creds->session.keytype = rep->enc_part.key.keytype;
    ret = krb5_data_copy (&creds->session.keyvalue,
			  rep->enc_part.key.keyvalue.data,
			  rep->enc_part.key.keyvalue.length);
    if (ret) {
	krb5_clear_error_message(context);
	goto out;
    }

    /* compare client and save */
    ret = _krb5_principalname2krb5_principal(context,
					     &tmp_principal,
					     rep->kdc_rep.cname,
					     rep->kdc_rep.crealm);
    if (ret)
	goto out;

    /* check client referral and save principal */
    /* anonymous here ? */
    if((flags & EXTRACT_TICKET_ALLOW_CNAME_MISMATCH) == 0) {
	ret = check_client_referral(context, rep,
				    creds->client,
				    tmp_principal,
				    &creds->session);
	if (ret) {
	    krb5_free_principal (context, tmp_principal);
	    goto out;
	}
    }
    krb5_free_principal (context, creds->client);
    creds->client = tmp_principal;

    /* check server referral and save principal */
    ret = _krb5_principalname2krb5_principal (context,
					      &tmp_principal,
					      rep->kdc_rep.ticket.sname,
					      rep->kdc_rep.ticket.realm);
    if (ret)
	goto out;
    if((flags & EXTRACT_TICKET_ALLOW_SERVER_MISMATCH) == 0){
	ret = check_server_referral(context,
				    rep,
				    flags,
				    creds->server,
				    tmp_principal,
				    &creds->session);
	if (ret) {
	    krb5_free_principal (context, tmp_principal);
	    goto out;
	}
    }
    krb5_free_principal(context, creds->server);
    creds->server = tmp_principal;

    /* verify names */
    if(flags & EXTRACT_TICKET_MATCH_REALM){
	const char *srealm = krb5_principal_get_realm(context, creds->server);
	const char *crealm = krb5_principal_get_realm(context, creds->client);

	if (strcmp(rep->enc_part.srealm, srealm) != 0 ||
	    strcmp(rep->enc_part.srealm, crealm) != 0)
	{
	    ret = KRB5KRB_AP_ERR_MODIFIED;
	    krb5_clear_error_message(context);
	    goto out;
	}
    }

    /* compare nonces */

    if (nonce != (unsigned)rep->enc_part.nonce) {
	ret = KRB5KRB_AP_ERR_MODIFIED;
	krb5_set_error_message(context, ret, N_("malloc: out of memory", ""));
	goto out;
    }

    /* set kdc-offset */

    krb5_timeofday (context, &sec_now);
    if (rep->enc_part.flags.initial
	&& (flags & EXTRACT_TICKET_TIMESYNC)
	&& context->kdc_sec_offset == 0
	&& krb5_config_get_bool (context, NULL,
				 "libdefaults",
				 "kdc_timesync",
				 NULL)) {
	context->kdc_sec_offset = rep->enc_part.authtime - sec_now;
	krb5_timeofday (context, &sec_now);
    }

    /* check all times */

    if (rep->enc_part.starttime) {
	tmp_time = *rep->enc_part.starttime;
    } else
	tmp_time = rep->enc_part.authtime;

    if (creds->times.starttime == 0
	&& labs(tmp_time - sec_now) > context->max_skew) {
	ret = KRB5KRB_AP_ERR_SKEW;
	krb5_set_error_message (context, ret,
				N_("time skew (%ld) larger than max (%ld)", ""),
			       labs(tmp_time - sec_now),
			       (long)context->max_skew);
	goto out;
    }

    if (creds->times.starttime != 0
	&& tmp_time != creds->times.starttime) {
	krb5_clear_error_message (context);
	ret = KRB5KRB_AP_ERR_MODIFIED;
	goto out;
    }

    creds->times.starttime = tmp_time;

    if (rep->enc_part.renew_till) {
	tmp_time = *rep->enc_part.renew_till;
    } else
	tmp_time = 0;

    if (creds->times.renew_till != 0
	&& tmp_time > creds->times.renew_till) {
	krb5_clear_error_message (context);
	ret = KRB5KRB_AP_ERR_MODIFIED;
	goto out;
    }

    creds->times.renew_till = tmp_time;

    creds->times.authtime = rep->enc_part.authtime;

    if (creds->times.endtime != 0
	&& rep->enc_part.endtime > creds->times.endtime) {
	krb5_clear_error_message (context);
	ret = KRB5KRB_AP_ERR_MODIFIED;
	goto out;
    }

    creds->times.endtime  = rep->enc_part.endtime;

    if(rep->enc_part.caddr)
	krb5_copy_addresses (context, rep->enc_part.caddr, &creds->addresses);
    else if(addrs)
	krb5_copy_addresses (context, addrs, &creds->addresses);
    else {
	creds->addresses.len = 0;
	creds->addresses.val = NULL;
    }
    creds->flags.b = rep->enc_part.flags;

    creds->authdata.len = 0;
    creds->authdata.val = NULL;

    /* extract ticket */
    ASN1_MALLOC_ENCODE(Ticket, creds->ticket.data, creds->ticket.length,
		       &rep->kdc_rep.ticket, &len, ret);
    if(ret)
	goto out;
    if (creds->ticket.length != len)
	krb5_abortx(context, "internal error in ASN.1 encoder");
    creds->second_ticket.length = 0;
    creds->second_ticket.data   = NULL;


out:
    memset (rep->enc_part.key.keyvalue.data, 0,
	    rep->enc_part.key.keyvalue.length);
    return ret;
}