CVE-2015-2695 (published 2015-11-09T03:59Z)

lib/gssapi/spnego/spnego_mech.c in MIT Kerberos 5 (aka krb5) before 1.14 relies on an inappropriate context handle, which allows remote attackers to cause a denial of service (incorrect pointer read and process crash) via a crafted SPNEGO packet that is mishandled during a gss_inquire_context call.

Severity: MEDIUM
CVSS v2 base score: 5.0 (AV:N/AC:L/Au:N/C:N/I:N/A:P)

Weakness information:
cwe_id: CWE-763
cwe_name: Release of Invalid Pointer or Reference
description: The product attempts to return a memory resource to the system, but it calls the wrong release function or calls the appropriate release function incorrectly.
extended_description: 
            This weakness can take several forms, such as:
               
                  The memory was allocated, explicitly or implicitly, via one memory management method and deallocated using a different, non-compatible function (CWE-762).
                  The function calls or memory management routines chosen are appropriate, however they are used incorrectly, such as in CWE-761.
               
         
         

Fix information:
repo_url: https://github.com/krb5/krb5
commit_details: repo_url: https://github.com/krb5/krb5
author: Nicolas Williams
author_date: 2015-09-14 12:27:52-04:00
msg: Fix SPNEGO context aliasing bugs [CVE-2015-2695]

The SPNEGO mechanism currently replaces its context handle with the
mechanism context handle upon establishment, under the assumption that
most GSS functions are only called after context establishment.  This
assumption is incorrect, and can lead to aliasing violations for some
programs.  Maintain the SPNEGO context structure after context
establishment and refer to it in all GSS methods.  Add initiate and
opened flags to the SPNEGO context structure for use in
gss_inquire_context() prior to context establishment.

CVE-2015-2695:

In MIT krb5 1.5 and later, applications which call
gss_inquire_context() on a partially-established SPNEGO context can
cause the GSS-API library to read from a pointer using the wrong type,
generally causing a process crash.  This bug may go unnoticed, because
the most common SPNEGO authentication scenario establishes the context
after just one call to gss_accept_sec_context().  Java server
applications using the native JGSS provider are vulnerable to this
bug.  A carefully crafted SPNEGO packet might allow the
gss_inquire_context() call to succeed with attacker-determined
results, but applications should not make access control decisions
based on gss_inquire_context() results prior to context establishment.

    CVSSv2 Vector: AV:N/AC:M/Au:N/C:N/I:N/A:C/E:POC/RL:OF/RC:C

[ghudson@mit.edu: several bugfixes, style changes, and edge-case
behavior changes; commit message and CVE description]

ticket: 8244
target_version: 1.14
tags: pullup
repository: repo_url: https://github.com/krb5/krb5
repo_name: krb5/krb5
description: mirror of MIT krb5 repository
repo_language: C
owner: krb5
file_changes: filename: gssapiP_spnego.h
change_type: ModificationType.MODIFY
diff: @@ -103,6 +103,8 @@ typedef struct {
 	int firstpass;
 	int mech_complete;
 	int nego_done;
+	int initiate;
+	int opened;
 	OM_uint32 ctx_flags;
 	gss_name_t internal_name;
 	gss_OID actual_mech;

programming_language: C
filename: spnego_mech.c
change_type: ModificationType.MODIFY
diff: @@ -102,7 +102,7 @@ static OM_uint32 get_negotiable_mechs(OM_uint32 *, spnego_gss_cred_id_t,
 				      gss_cred_usage_t, gss_OID_set *);
 static void release_spnego_ctx(spnego_gss_ctx_id_t *);
 static void check_spnego_options(spnego_gss_ctx_id_t);
-static spnego_gss_ctx_id_t create_spnego_ctx(void);
+static spnego_gss_ctx_id_t create_spnego_ctx(int);
 static int put_mech_set(gss_OID_set mechSet, gss_buffer_t buf);
 static int put_input_token(unsigned char **, gss_buffer_t, unsigned int);
 static int put_mech_oid(unsigned char **, gss_OID_const, unsigned int);
@@ -454,7 +454,7 @@ check_spnego_options(spnego_gss_ctx_id_t spnego_ctx)
 }
 
 static spnego_gss_ctx_id_t
-create_spnego_ctx(void)
+create_spnego_ctx(int initiate)
 {
 	spnego_gss_ctx_id_t spnego_ctx = NULL;
 	spnego_ctx = (spnego_gss_ctx_id_t)
@@ -477,6 +477,8 @@ create_spnego_ctx(void)
 	spnego_ctx->mic_rcvd = 0;
 	spnego_ctx->mech_complete = 0;
 	spnego_ctx->nego_done = 0;
+	spnego_ctx->opened = 0;
+	spnego_ctx->initiate = initiate;
 	spnego_ctx->internal_name = GSS_C_NO_NAME;
 	spnego_ctx->actual_mech = GSS_C_NO_OID;
 
@@ -642,7 +644,7 @@ init_ctx_new(OM_uint32 *minor_status,
 	OM_uint32 ret;
 	spnego_gss_ctx_id_t sc = NULL;
 
-	sc = create_spnego_ctx();
+	sc = create_spnego_ctx(1);
 	if (sc == NULL)
 		return GSS_S_FAILURE;
 
@@ -659,10 +661,7 @@ init_ctx_new(OM_uint32 *minor_status,
 		ret = GSS_S_FAILURE;
 		goto cleanup;
 	}
-	/*
-	 * The actual context is not yet determined, set the output
-	 * context handle to refer to the spnego context itself.
-	 */
+
 	sc->ctx_handle = GSS_C_NO_CONTEXT;
 	*ctx = (gss_ctx_id_t)sc;
 	sc = NULL;
@@ -1108,16 +1107,11 @@ cleanup:
 	}
 	gss_release_buffer(&tmpmin, &mechtok_out);
 	if (ret == GSS_S_COMPLETE) {
-		/*
-		 * Now, switch the output context to refer to the
-		 * negotiated mechanism's context.
-		 */
-		*context_handle = (gss_ctx_id_t)spnego_ctx->ctx_handle;
+		spnego_ctx->opened = 1;
 		if (actual_mech != NULL)
 			*actual_mech = spnego_ctx->actual_mech;
 		if (ret_flags != NULL)
 			*ret_flags = spnego_ctx->ctx_flags;
-		release_spnego_ctx(&spnego_ctx);
 	} else if (ret != GSS_S_CONTINUE_NEEDED) {
 		if (spnego_ctx != NULL) {
 			gss_delete_sec_context(&tmpmin,
@@ -1285,7 +1279,7 @@ acc_ctx_hints(OM_uint32 *minor_status,
 	if (ret != GSS_S_COMPLETE)
 		goto cleanup;
 
-	sc = create_spnego_ctx();
+	sc = create_spnego_ctx(0);
 	if (sc == NULL) {
 		ret = GSS_S_FAILURE;
 		goto cleanup;
@@ -1367,7 +1361,7 @@ acc_ctx_new(OM_uint32 *minor_status,
 		gss_release_buffer(&tmpmin, &sc->DER_mechTypes);
 		assert(mech_wanted != GSS_C_NO_OID);
 	} else
-		sc = create_spnego_ctx();
+		sc = create_spnego_ctx(0);
 	if (sc == NULL) {
 		ret = GSS_S_FAILURE;
 		*return_token = NO_TOKEN_SEND;
@@ -1750,13 +1744,12 @@ cleanup:
 			ret = GSS_S_FAILURE;
 	}
 	if (ret == GSS_S_COMPLETE) {
-		*context_handle = (gss_ctx_id_t)sc->ctx_handle;
+		sc->opened = 1;
 		if (sc->internal_name != GSS_C_NO_NAME &&
 		    src_name != NULL) {
 			*src_name = sc->internal_name;
 			sc->internal_name = GSS_C_NO_NAME;
 		}
-		release_spnego_ctx(&sc);
 	} else if (ret != GSS_S_CONTINUE_NEEDED) {
 		if (sc != NULL) {
 			gss_delete_sec_context(&tmpmin, &sc->ctx_handle,
@@ -2069,8 +2062,13 @@ spnego_gss_unwrap(
 		gss_qop_t *qop_state)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_NO_CONTEXT);
+
 	ret = gss_unwrap(minor_status,
-			context_handle,
+			sc->ctx_handle,
 			input_message_buffer,
 			output_message_buffer,
 			conf_state,
@@ -2090,8 +2088,13 @@ spnego_gss_wrap(
 		gss_buffer_t output_message_buffer)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_NO_CONTEXT);
+
 	ret = gss_wrap(minor_status,
-		    context_handle,
+		    sc->ctx_handle,
 		    conf_req_flag,
 		    qop_req,
 		    input_message_buffer,
@@ -2108,8 +2111,14 @@ spnego_gss_process_context_token(
 				const gss_buffer_t token_buffer)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	/* SPNEGO doesn't have its own context tokens. */
+	if (!sc->opened)
+		return (GSS_S_DEFECTIVE_TOKEN);
+
 	ret = gss_process_context_token(minor_status,
-					context_handle,
+					sc->ctx_handle,
 					token_buffer);
 
 	return (ret);
@@ -2133,19 +2142,9 @@ spnego_gss_delete_sec_context(
 	if (*ctx == NULL)
 		return (GSS_S_COMPLETE);
 
-	/*
-	 * If this is still an SPNEGO mech, release it locally.
-	 */
-	if ((*ctx)->magic_num == SPNEGO_MAGIC_ID) {
-		(void) gss_delete_sec_context(minor_status,
-				    &(*ctx)->ctx_handle,
-				    output_token);
-		(void) release_spnego_ctx(ctx);
-	} else {
-		ret = gss_delete_sec_context(minor_status,
-				    context_handle,
-				    output_token);
-	}
+	(void) gss_delete_sec_context(minor_status, &(*ctx)->ctx_handle,
+				      output_token);
+	(void) release_spnego_ctx(ctx);
 
 	return (ret);
 }
@@ -2157,8 +2156,13 @@ spnego_gss_context_time(
 			OM_uint32	*time_rec)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_NO_CONTEXT);
+
 	ret = gss_context_time(minor_status,
-			    context_handle,
+			    sc->ctx_handle,
 			    time_rec);
 	return (ret);
 }
@@ -2170,9 +2174,20 @@ spnego_gss_export_sec_context(
 			    gss_buffer_t interprocess_token)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = *(spnego_gss_ctx_id_t *)context_handle;
+
+	/* We don't currently support exporting partially established
+	 * contexts. */
+	if (!sc->opened)
+		return GSS_S_UNAVAILABLE;
+
 	ret = gss_export_sec_context(minor_status,
-				    context_handle,
+				    &sc->ctx_handle,
 				    interprocess_token);
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT) {
+		release_spnego_ctx(&sc);
+		*context_handle = GSS_C_NO_CONTEXT;
+	}
 	return (ret);
 }
 
@@ -2182,11 +2197,12 @@ spnego_gss_import_sec_context(
 	const gss_buffer_t	interprocess_token,
 	gss_ctx_id_t		*context_handle)
 {
-	OM_uint32 ret;
-	ret = gss_import_sec_context(minor_status,
-				    interprocess_token,
-				    context_handle);
-	return (ret);
+	/*
+	 * Until we implement partial context exports, there are no SPNEGO
+	 * exported context tokens, only tokens for underlying mechs.  So just
+	 * return an error for now.
+	 */
+	return GSS_S_UNAVAILABLE;
 }
 #endif /* LEAN_CLIENT */
 
@@ -2203,16 +2219,48 @@ spnego_gss_inquire_context(
 			int		*opened)
 {
 	OM_uint32 ret = GSS_S_COMPLETE;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	if (src_name != NULL)
+		*src_name = GSS_C_NO_NAME;
+	if (targ_name != NULL)
+		*targ_name = GSS_C_NO_NAME;
+	if (lifetime_rec != NULL)
+		*lifetime_rec = 0;
+	if (mech_type != NULL)
+		*mech_type = (gss_OID)gss_mech_spnego;
+	if (ctx_flags != NULL)
+		*ctx_flags = 0;
+	if (locally_initiated != NULL)
+		*locally_initiated = sc->initiate;
+	if (opened != NULL)
+		*opened = sc->opened;
+
+	if (sc->ctx_handle != GSS_C_NO_CONTEXT) {
+		ret = gss_inquire_context(minor_status, sc->ctx_handle,
+					  src_name, targ_name, lifetime_rec,
+					  mech_type, ctx_flags, NULL, NULL);
+	}
 
-	ret = gss_inquire_context(minor_status,
-				context_handle,
-				src_name,
-				targ_name,
-				lifetime_rec,
-				mech_type,
-				ctx_flags,
-				locally_initiated,
-				opened);
+	if (!sc->opened) {
+		/*
+		 * We are still doing SPNEGO negotiation, so report SPNEGO as
+		 * the OID.  After negotiation is complete we will report the
+		 * underlying mechanism OID.
+		 */
+		if (mech_type != NULL)
+			*mech_type = (gss_OID)gss_mech_spnego;
+
+		/*
+		 * Remove flags we don't support with partially-established
+		 * contexts.  (Change this to keep GSS_C_TRANS_FLAG if we add
+		 * support for exporting partial SPNEGO contexts.)
+		 */
+		if (ctx_flags != NULL) {
+			*ctx_flags &= ~GSS_C_PROT_READY_FLAG;
+			*ctx_flags &= ~GSS_C_TRANS_FLAG;
+		}
+	}
 
 	return (ret);
 }
@@ -2227,8 +2275,13 @@ spnego_gss_wrap_size_limit(
 	OM_uint32	*max_input_size)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_NO_CONTEXT);
+
 	ret = gss_wrap_size_limit(minor_status,
-				context_handle,
+				sc->ctx_handle,
 				conf_req_flag,
 				qop_req,
 				req_output_size,
@@ -2245,8 +2298,13 @@ spnego_gss_get_mic(
 		gss_buffer_t message_token)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_NO_CONTEXT);
+
 	ret = gss_get_mic(minor_status,
-		    context_handle,
+		    sc->ctx_handle,
 		    qop_req,
 		    message_buffer,
 		    message_token);
@@ -2262,8 +2320,13 @@ spnego_gss_verify_mic(
 		gss_qop_t *qop_state)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_NO_CONTEXT);
+
 	ret = gss_verify_mic(minor_status,
-			    context_handle,
+			    sc->ctx_handle,
 			    msg_buffer,
 			    token_buffer,
 			    qop_state);
@@ -2278,8 +2341,14 @@ spnego_gss_inquire_sec_context_by_oid(
 		gss_buffer_set_t *data_set)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	/* There are no SPNEGO-specific OIDs for this function. */
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_UNAVAILABLE);
+
 	ret = gss_inquire_sec_context_by_oid(minor_status,
-			    context_handle,
+			    sc->ctx_handle,
 			    desired_object,
 			    data_set);
 	return (ret);
@@ -2359,8 +2428,15 @@ spnego_gss_set_sec_context_option(
 		const gss_buffer_t value)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)*context_handle;
+
+	/* There are no SPNEGO-specific OIDs for this function, and we cannot
+	 * construct an empty SPNEGO context with it. */
+	if (sc == NULL || sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_UNAVAILABLE);
+
 	ret = gss_set_sec_context_option(minor_status,
-			    context_handle,
+			    &sc->ctx_handle,
 			    desired_object,
 			    value);
 	return (ret);
@@ -2377,8 +2453,13 @@ spnego_gss_wrap_aead(OM_uint32 *minor_status,
 		     gss_buffer_t output_message_buffer)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_NO_CONTEXT);
+
 	ret = gss_wrap_aead(minor_status,
-			    context_handle,
+			    sc->ctx_handle,
 			    conf_req_flag,
 			    qop_req,
 			    input_assoc_buffer,
@@ -2399,8 +2480,13 @@ spnego_gss_unwrap_aead(OM_uint32 *minor_status,
 		       gss_qop_t *qop_state)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_NO_CONTEXT);
+
 	ret = gss_unwrap_aead(minor_status,
-			      context_handle,
+			      sc->ctx_handle,
 			      input_message_buffer,
 			      input_assoc_buffer,
 			      output_payload_buffer,
@@ -2419,8 +2505,13 @@ spnego_gss_wrap_iov(OM_uint32 *minor_status,
 		    int iov_count)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_NO_CONTEXT);
+
 	ret = gss_wrap_iov(minor_status,
-			   context_handle,
+			   sc->ctx_handle,
 			   conf_req_flag,
 			   qop_req,
 			   conf_state,
@@ -2438,8 +2529,13 @@ spnego_gss_unwrap_iov(OM_uint32 *minor_status,
 		      int iov_count)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_NO_CONTEXT);
+
 	ret = gss_unwrap_iov(minor_status,
-			     context_handle,
+			     sc->ctx_handle,
 			     conf_state,
 			     qop_state,
 			     iov,
@@ -2457,8 +2553,13 @@ spnego_gss_wrap_iov_length(OM_uint32 *minor_status,
 			   int iov_count)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_NO_CONTEXT);
+
 	ret = gss_wrap_iov_length(minor_status,
-				  context_handle,
+				  sc->ctx_handle,
 				  conf_req_flag,
 				  qop_req,
 				  conf_state,
@@ -2475,8 +2576,13 @@ spnego_gss_complete_auth_token(
 		gss_buffer_t input_message_buffer)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_UNAVAILABLE);
+
 	ret = gss_complete_auth_token(minor_status,
-				      context_handle,
+				      sc->ctx_handle,
 				      input_message_buffer);
 	return (ret);
 }
@@ -2721,8 +2827,13 @@ spnego_gss_pseudo_random(OM_uint32 *minor_status,
 			 gss_buffer_t prf_out)
 {
 	OM_uint32 ret;
+	spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context;
+
+	if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+		return (GSS_S_NO_CONTEXT);
+
 	ret = gss_pseudo_random(minor_status,
-				context,
+				sc->ctx_handle,
 				prf_key,
 				prf_in,
 				desired_output_len,
@@ -2863,7 +2974,12 @@ spnego_gss_get_mic_iov(OM_uint32 *minor_status, gss_ctx_id_t context_handle,
 		       gss_qop_t qop_req, gss_iov_buffer_desc *iov,
 		       int iov_count)
 {
-    return gss_get_mic_iov(minor_status, context_handle, qop_req, iov,
+    spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+    if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+	    return (GSS_S_NO_CONTEXT);
+
+    return gss_get_mic_iov(minor_status, sc->ctx_handle, qop_req, iov,
 			   iov_count);
 }
 
@@ -2872,7 +2988,12 @@ spnego_gss_verify_mic_iov(OM_uint32 *minor_status, gss_ctx_id_t context_handle,
 			  gss_qop_t *qop_state, gss_iov_buffer_desc *iov,
 			  int iov_count)
 {
-    return gss_verify_mic_iov(minor_status, context_handle, qop_state, iov,
+    spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+    if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+	    return (GSS_S_NO_CONTEXT);
+
+    return gss_verify_mic_iov(minor_status, sc->ctx_handle, qop_state, iov,
 			      iov_count);
 }
 
@@ -2881,7 +3002,12 @@ spnego_gss_get_mic_iov_length(OM_uint32 *minor_status,
 			      gss_ctx_id_t context_handle, gss_qop_t qop_req,
 			      gss_iov_buffer_desc *iov, int iov_count)
 {
-    return gss_get_mic_iov_length(minor_status, context_handle, qop_req, iov,
+    spnego_gss_ctx_id_t sc = (spnego_gss_ctx_id_t)context_handle;
+
+    if (sc->ctx_handle == GSS_C_NO_CONTEXT)
+	    return (GSS_S_NO_CONTEXT);
+
+    return gss_get_mic_iov_length(minor_status, sc->ctx_handle, qop_req, iov,
 				  iov_count);
 }
 

programming_language: C