Attachment 15523 Details for Bug 49349 – CVE-2023-48795

[patch] CVE-2023-48795

6e43be5c7b99dbee49dc72b6f989f29fdd7e9356.patch (text/plain), 5.91 KB, created by Александр on 2024-02-10 18:05:42 MSK

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Creator: Александр

Created: 2024-02-10 18:05:42 MSK

Size: 5.91 KB

patch

obsolete

>From 6e43be5c7b99dbee49dc72b6f989f29fdd7e9356 Mon Sep 17 00:00:00 2001
>From: Matt Johnston <matt@ucc.asn.au>
>Date: Mon, 20 Nov 2023 14:02:47 +0800
>Subject: [PATCH] Implement Strict KEX mode
>
>As specified by OpenSSH with kex-strict-c-v00@openssh.com and
>kex-strict-s-v00@openssh.com.
>---
> cli-session.c    | 11 +++++++++++
> common-algo.c    |  6 ++++++
> common-kex.c     | 26 +++++++++++++++++++++++++-
> kex.h            |  3 +++
> process-packet.c | 34 +++++++++++++++++++---------------
> ssh.h            |  4 ++++
> svr-session.c    |  3 +++
> 7 files changed, 71 insertions(+), 16 deletions(-)
>
>diff --git a/cli-session.c b/cli-session.c
>index 5981b2470..d261c8f82 100644
>--- a/cli-session.c
>+++ b/cli-session.c
>@@ -46,6 +46,7 @@ static void cli_finished(void) ATTRIB_NORETURN;
> static void recv_msg_service_accept(void);
> static void cli_session_cleanup(void);
> static void recv_msg_global_request_cli(void);
>+static void cli_algos_initialise(void);
> 
> struct clientsession cli_ses; /* GLOBAL */
> 
>@@ -117,6 +118,7 @@ void cli_session(int sock_in, int sock_out, struct dropbear_progress_connection
> 	}
> 
> 	chaninitialise(cli_chantypes);
>+	cli_algos_initialise();
> 
> 	/* Set up cli_ses vars */
> 	cli_session_init(proxy_cmd_pid);
>@@ -487,3 +489,12 @@ void cli_dropbear_log(int priority, const char* format, va_list param) {
> 	fflush(stderr);
> }
> 
>+static void cli_algos_initialise(void) {
>+	algo_type *algo;
>+	for (algo = sshkex; algo->name; algo++) {
>+		if (strcmp(algo->name, SSH_STRICT_KEX_S) == 0) {
>+			algo->usable = 0;
>+		}
>+	}
>+}
>+
>diff --git a/common-algo.c b/common-algo.c
>index 378f0ca8e..f9d46ebb6 100644
>--- a/common-algo.c
>+++ b/common-algo.c
>@@ -307,6 +307,12 @@ algo_type sshkex[] = {
> 	/* Set unusable by svr_algos_initialise() */
> 	{SSH_EXT_INFO_C, 0, NULL, 1, NULL},
> #endif
>+#endif
>+#if DROPBEAR_CLIENT
>+	{SSH_STRICT_KEX_C, 0, NULL, 1, NULL},
>+#endif
>+#if DROPBEAR_SERVER
>+	{SSH_STRICT_KEX_S, 0, NULL, 1, NULL},
> #endif
> 	{NULL, 0, NULL, 0, NULL}
> };
>diff --git a/common-kex.c b/common-kex.c
>index ac8844246..8e33b12a6 100644
>--- a/common-kex.c
>+++ b/common-kex.c
>@@ -183,6 +183,10 @@ void send_msg_newkeys() {
> 	gen_new_keys();
> 	switch_keys();
> 
>+	if (ses.kexstate.strict_kex) {
>+		ses.transseq = 0;
>+	}
>+
> 	TRACE(("leave send_msg_newkeys"))
> }
> 
>@@ -193,7 +197,11 @@ void recv_msg_newkeys() {
> 
> 	ses.kexstate.recvnewkeys = 1;
> 	switch_keys();
>-	
>+
>+	if (ses.kexstate.strict_kex) {
>+		ses.recvseq = 0;
>+	}
>+
> 	TRACE(("leave recv_msg_newkeys"))
> }
> 
>@@ -550,6 +558,10 @@ void recv_msg_kexinit() {
> 
> 	ses.kexstate.recvkexinit = 1;
> 
>+	if (ses.kexstate.strict_kex && !ses.kexstate.donefirstkex && ses.recvseq != 1) {
>+		dropbear_exit("First packet wasn't kexinit");
>+	}
>+
> 	TRACE(("leave recv_msg_kexinit"))
> }
> 
>@@ -859,6 +871,18 @@ static void read_kex_algos() {
> 	}
> #endif
> 
>+	if (!ses.kexstate.donefirstkex) {
>+		const char* strict_name;
>+		if (IS_DROPBEAR_CLIENT) {
>+			strict_name = SSH_STRICT_KEX_S;
>+		} else {
>+			strict_name = SSH_STRICT_KEX_C;
>+		}
>+		if (buf_has_algo(ses.payload, strict_name) == DROPBEAR_SUCCESS) {
>+			ses.kexstate.strict_kex = 1;
>+		}
>+	}
>+
> 	algo = buf_match_algo(ses.payload, sshkex, kexguess2, &goodguess);
> 	allgood &= goodguess;
> 	if (algo == NULL || algo->data == NULL) {
>diff --git a/kex.h b/kex.h
>index 77cf21a37..7fcc3c252 100644
>--- a/kex.h
>+++ b/kex.h
>@@ -83,6 +83,9 @@ struct KEXState {
> 
> 	unsigned our_first_follows_matches : 1;
> 
>+	/* Boolean indicating that strict kex mode is in use */
>+	unsigned int strict_kex;
>+
> 	time_t lastkextime; /* time of the last kex */
> 	unsigned int datatrans; /* data transmitted since last kex */
> 	unsigned int datarecv; /* data received since last kex */
>diff --git a/process-packet.c b/process-packet.c
>index 945416023..133a152d0 100644
>--- a/process-packet.c
>+++ b/process-packet.c
>@@ -44,6 +44,7 @@ void process_packet() {
> 
> 	unsigned char type;
> 	unsigned int i;
>+	unsigned int first_strict_kex = ses.kexstate.strict_kex && !ses.kexstate.donefirstkex;
> 	time_t now;
> 
> 	TRACE2(("enter process_packet"))
>@@ -54,22 +55,24 @@ void process_packet() {
> 	now = monotonic_now();
> 	ses.last_packet_time_keepalive_recv = now;
> 
>-	/* These packets we can receive at any time */
>-	switch(type) {
> 
>-		case SSH_MSG_IGNORE:
>-			goto out;
>-		case SSH_MSG_DEBUG:
>-			goto out;
>+	if (type == SSH_MSG_DISCONNECT) {
>+		/* Allowed at any time */
>+		dropbear_close("Disconnect received");
>+	}
> 
>-		case SSH_MSG_UNIMPLEMENTED:
>-			/* debugging XXX */
>-			TRACE(("SSH_MSG_UNIMPLEMENTED"))
>-			goto out;
>-			
>-		case SSH_MSG_DISCONNECT:
>-			/* TODO cleanup? */
>-			dropbear_close("Disconnect received");
>+	/* These packets may be received at any time,
>+	   except during first kex with strict kex */
>+	if (!first_strict_kex) {
>+		switch(type) {
>+			case SSH_MSG_IGNORE:
>+				goto out;
>+			case SSH_MSG_DEBUG:
>+				goto out;
>+			case SSH_MSG_UNIMPLEMENTED:
>+				TRACE(("SSH_MSG_UNIMPLEMENTED"))
>+				goto out;
>+		}
> 	}
> 
> 	/* Ignore these packet types so that keepalives don't interfere with
>@@ -98,7 +101,8 @@ void process_packet() {
> 			if (type >= 1 && type <= 49
> 				&& type != SSH_MSG_SERVICE_REQUEST
> 				&& type != SSH_MSG_SERVICE_ACCEPT
>-				&& type != SSH_MSG_KEXINIT)
>+				&& type != SSH_MSG_KEXINIT
>+				&& !first_strict_kex)
> 			{
> 				TRACE(("unknown allowed packet during kexinit"))
> 				recv_unimplemented();
>diff --git a/ssh.h b/ssh.h
>index 1b4fec65f..ef3efdca0 100644
>--- a/ssh.h
>+++ b/ssh.h
>@@ -100,6 +100,10 @@
> #define SSH_EXT_INFO_C "ext-info-c"
> #define SSH_SERVER_SIG_ALGS "server-sig-algs"
> 
>+/* OpenSSH strict KEX feature */
>+#define SSH_STRICT_KEX_S "kex-strict-s-v00@openssh.com"
>+#define SSH_STRICT_KEX_C "kex-strict-c-v00@openssh.com"
>+
> /* service types */
> #define SSH_SERVICE_USERAUTH "ssh-userauth"
> #define SSH_SERVICE_USERAUTH_LEN 12
>diff --git a/svr-session.c b/svr-session.c
>index 769f0731d..a538e2c5c 100644
>--- a/svr-session.c
>+++ b/svr-session.c
>@@ -370,6 +370,9 @@ static void svr_algos_initialise(void) {
> 			algo->usable = 0;
> 		}
> #endif
>+		if (strcmp(algo->name, SSH_STRICT_KEX_C) == 0) {
>+			algo->usable = 0;
>+		}
> 	}
> }
>

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Attachments on bug 49349: 15523