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From e3b5a5e5267818c97750b266df50b6a3d4649604 Mon Sep 17 00:00:00 2001
From: Greg Hudson <ghudson@mit.edu>
Date: Tue, 24 Mar 2015 12:02:37 -0400
Subject: [PATCH] Prevent requires_preauth bypass [CVE-2015-2694]
In the OTP kdcpreauth module, don't set the TKT_FLG_PRE_AUTH bit until
the request is successfully verified. In the PKINIT kdcpreauth
module, don't respond with code 0 on empty input or an unconfigured
realm. Together these bugs could cause the KDC preauth framework to
erroneously treat a request as pre-authenticated.
CVE-2015-2694:
In MIT krb5 1.12 and later, when the KDC is configured with PKINIT
support, an unauthenticated remote attacker can bypass the
requires_preauth flag on a client principal and obtain a ciphertext
encrypted in the principal's long-term key. This ciphertext could be
used to conduct an off-line dictionary attack against the user's
password.
CVSSv2 Vector: AV:N/AC:M/Au:N/C:P/I:P/A:N/E:POC/RL:OF/RC:C
ticket: 8160 (new)
target_version: 1.13.2
tags: pullup
subject: requires_preauth bypass in PKINIT-enabled KDC [CVE-2015-2694]
---
src/plugins/preauth/otp/main.c | 10 +++++++---
src/plugins/preauth/pkinit/pkinit_srv.c | 4 ++--
2 files changed, 9 insertions(+), 5 deletions(-)
diff --git a/src/plugins/preauth/otp/main.c b/src/plugins/preauth/otp/main.c
index bf9c6a8..7941b4a 100644
--- a/src/plugins/preauth/otp/main.c
+++ b/src/plugins/preauth/otp/main.c
@@ -42,6 +42,7 @@ static krb5_preauthtype otp_pa_type_list[] =
struct request_state {
krb5_kdcpreauth_verify_respond_fn respond;
void *arg;
+ krb5_enc_tkt_part *enc_tkt_reply;
};
static krb5_error_code
@@ -159,6 +160,9 @@ on_response(void *data, krb5_error_code retval, otp_response response)
if (retval == 0 && response != otp_response_success)
retval = KRB5_PREAUTH_FAILED;
+ if (retval == 0)
+ rs.enc_tkt_reply->flags |= TKT_FLG_PRE_AUTH;
+
rs.respond(rs.arg, retval, NULL, NULL, NULL);
}
@@ -263,8 +267,6 @@ otp_verify(krb5_context context, krb5_data *req_pkt, krb5_kdc_req *request,
krb5_data d, plaintext;
char *config;
- enc_tkt_reply->flags |= TKT_FLG_PRE_AUTH;
-
/* Get the FAST armor key. */
armor_key = cb->fast_armor(context, rock);
if (armor_key == NULL) {
@@ -298,12 +300,14 @@ otp_verify(krb5_context context, krb5_data *req_pkt, krb5_kdc_req *request,
goto error;
}
- /* Create the request state. */
+ /* Create the request state. Save the response callback, and the
+ * enc_tkt_reply pointer so we can set the TKT_FLG_PRE_AUTH flag later. */
rs = k5alloc(sizeof(struct request_state), &retval);
if (rs == NULL)
goto error;
rs->arg = arg;
rs->respond = respond;
+ rs->enc_tkt_reply = enc_tkt_reply;
/* Get the principal's OTP configuration string. */
retval = cb->get_string(context, rock, "otp", &config);
diff --git a/src/plugins/preauth/pkinit/pkinit_srv.c b/src/plugins/preauth/pkinit/pkinit_srv.c
index b472741..5b1d73e 100644
--- a/src/plugins/preauth/pkinit/pkinit_srv.c
+++ b/src/plugins/preauth/pkinit/pkinit_srv.c
@@ -301,7 +301,7 @@ pkinit_server_verify_padata(krb5_context context,
pkiDebug("pkinit_verify_padata: entered!\n");
if (data == NULL || data->length <= 0 || data->contents == NULL) {
- (*respond)(arg, 0, NULL, NULL, NULL);
+ (*respond)(arg, EINVAL, NULL, NULL, NULL);
return;
}
@@ -313,7 +313,7 @@ pkinit_server_verify_padata(krb5_context context,
plgctx = pkinit_find_realm_context(context, moddata, request->server);
if (plgctx == NULL) {
- (*respond)(arg, 0, NULL, NULL, NULL);
+ (*respond)(arg, EINVAL, NULL, NULL, NULL);
return;
}
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