new file mode 100644
@@ -0,0 +1,234 @@
+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.
+
+CVE: CVE-2023-48795
+Upstream-Status: Backport [https://github.com/mkj/dropbear/commit/6e43be5c7b99dbee49dc72b6f989f29fdd7e9356]
+
+Signed-off-by: Peter Marko <peter.marko@siemens.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 5981b24..d261c8f 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 378f0ca..f9d46eb 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 ac88442..8e33b12 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 77cf21a..7fcc3c2 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 9454160..133a152 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 1b4fec6..ef3efdc 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 769f073..a538e2c 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;
++ }
+ }
+ }
+
@@ -22,6 +22,7 @@ SRC_URI = "http://matt.ucc.asn.au/dropbear/releases/dropbear-${PV}.tar.bz2 \
${@bb.utils.contains('DISTRO_FEATURES', 'pam', '${PAM_SRC_URI}', '', d)} \
${@bb.utils.contains('PACKAGECONFIG', 'disable-weak-ciphers', 'file://dropbear-disable-weak-ciphers.patch', '', d)} \
file://CVE-2023-36328.patch \
+ file://CVE-2023-48795.patch \
"
SRC_URI[sha256sum] = "bc5a121ffbc94b5171ad5ebe01be42746d50aa797c9549a4639894a16749443b"