File openssh-cve-2023-48795.patch of Package openssh.33331
Index: openssh-8.4p1/PROTOCOL
===================================================================
--- openssh-8.4p1.orig/PROTOCOL
+++ openssh-8.4p1/PROTOCOL
@@ -102,6 +102,25 @@ OpenSSH supports the use of ECDH in Curv
described at:
http://git.libssh.org/users/aris/libssh.git/plain/doc/curve25519-sha256@libssh.org.txt?h=curve25519
+1.9 transport: strict key exchange extension
+
+OpenSSH supports a number of transport-layer hardening measures under
+a "strict KEX" feature. This feature is signalled similarly to the
+RFC8305 ext-info feature: by including a additional algorithm in the
+SSH2_MSG_KEXINIT kex_algorithms field. The client may append
+"kex-strict-c-v00@openssh.com" to its kex_algorithms and the server
+may append "kex-strict-s-v00@openssh.com".
+
+When endpoint that supports this extension observes this algorithm
+name in a peer's KEXINIT packet, it MUST make the following changes to
+the the protocol:
+
+a) During initial KEX, terminate the connection if any unexpected or
+ out-of-sequence packet is received. This includes terminating the
+ connection if the first packet received is not SSH2_MSG_KEXINIT.
+b) At each SSH2_MSG_NEWKEYS message, reset the packet sequence number
+ to zero.
+
2. Connection protocol changes
2.1. connection: Channel write close extension "eow@openssh.com"
Index: openssh-8.4p1/kex.c
===================================================================
--- openssh-8.4p1.orig/kex.c
+++ openssh-8.4p1/kex.c
@@ -72,7 +72,7 @@
#include "fips.h"
/* prototype */
-static int kex_choose_conf(struct ssh *);
+static int kex_choose_conf(struct ssh *, uint32_t seq);
static int kex_input_newkeys(int, u_int32_t, struct ssh *);
static const char *proposal_names[PROPOSAL_MAX] = {
@@ -255,6 +255,24 @@ kex_names_valid(const char *names)
return 1;
}
+/* returns non-zero if proposal contains any algorithm from algs */
+static int
+has_any_alg(const char *proposal, const char *algs)
+{
+ char *cp;
+
+ if ((cp = match_list(proposal, algs, NULL)) == NULL)
+ return 0;
+ free(cp);
+ return 1;
+}
+
+static int
+kexalgs_contains (char **peer, const char *ext)
+{
+ return has_any_alg(peer[PROPOSAL_KEX_ALGS], ext);
+}
+
/*
* Concatenate algorithm names, avoiding duplicates in the process.
* Caller must free returned string.
@@ -262,7 +280,7 @@ kex_names_valid(const char *names)
char *
kex_names_cat(const char *a, const char *b)
{
- char *ret = NULL, *tmp = NULL, *cp, *p, *m;
+ char *ret = NULL, *tmp = NULL, *cp, *p;
size_t len;
if (a == NULL || *a == '\0')
@@ -279,10 +297,8 @@ kex_names_cat(const char *a, const char
}
strlcpy(ret, a, len);
for ((p = strsep(&cp, ",")); p && *p != '\0'; (p = strsep(&cp, ","))) {
- if ((m = match_list(ret, p, NULL)) != NULL) {
- free(m);
+ if (has_any_alg(ret, p))
continue; /* Algorithm already present */
- }
if (strlcat(ret, ",", len) >= len ||
strlcat(ret, p, len) >= len) {
free(tmp);
@@ -514,7 +530,12 @@ kex_protocol_error(int type, u_int32_t s
{
int r;
- error("kex protocol error: type %d seq %u", type, seq);
+ /* If in strict mode, any unexpected message is an error */
+ if ((ssh->kex->flags & KEX_INITIAL) && ssh->kex->kex_strict) {
+ ssh_packet_disconnect(ssh, "strict KEX violation: "
+ "unexpected packet type %u (seqnr %u)", type, seq);
+ }
+ error("type %u seq %u", type, seq);
if ((r = sshpkt_start(ssh, SSH2_MSG_UNIMPLEMENTED)) != 0 ||
(r = sshpkt_put_u32(ssh, seq)) != 0 ||
(r = sshpkt_send(ssh)) != 0)
@@ -586,6 +607,11 @@ kex_input_ext_info(int type, u_int32_t s
ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, &kex_protocol_error);
if ((r = sshpkt_get_u32(ssh, &ninfo)) != 0)
return r;
+ if (ninfo >= 1024) {
+ error("SSH2_MSG_EXT_INFO with too many entries, expected "
+ "<=1024, received %u", ninfo);
+ return dispatch_protocol_error(type, seq, ssh);
+ }
for (i = 0; i < ninfo; i++) {
if ((r = sshpkt_get_cstring(ssh, &name, NULL)) != 0)
return r;
@@ -686,7 +712,7 @@ kex_input_kexinit(int type, u_int32_t se
error("%s: no hex", __func__);
return SSH_ERR_INTERNAL_ERROR;
}
- ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, NULL);
+ ssh_dispatch_set(ssh, SSH2_MSG_KEXINIT, &kex_protocol_error);
ptr = sshpkt_ptr(ssh, &dlen);
if ((r = sshbuf_put(kex->peer, ptr, dlen)) != 0)
return r;
@@ -722,7 +748,7 @@ kex_input_kexinit(int type, u_int32_t se
if (!(kex->flags & KEX_INIT_SENT))
if ((r = kex_send_kexinit(ssh)) != 0)
return r;
- if ((r = kex_choose_conf(ssh)) != 0)
+ if ((r = kex_choose_conf(ssh, seq)) != 0)
return r;
if (kex->kex_type < KEX_MAX && kex->kex[kex->kex_type] != NULL)
@@ -999,7 +1025,7 @@ proposals_match(char *my[PROPOSAL_MAX],
}
static int
-kex_choose_conf(struct ssh *ssh)
+kex_choose_conf(struct ssh *ssh, uint32_t seq)
{
struct kex *kex = ssh->kex;
struct newkeys *newkeys;
@@ -1024,13 +1050,23 @@ kex_choose_conf(struct ssh *ssh)
sprop=peer;
}
- /* Check whether client supports ext_info_c */
- if (kex->server && (kex->flags & KEX_INITIAL)) {
- char *ext;
-
- ext = match_list("ext-info-c", peer[PROPOSAL_KEX_ALGS], NULL);
- kex->ext_info_c = (ext != NULL);
- free(ext);
+ /* Check whether peer supports ext_info/kex_strict */
+ if ((kex->flags & KEX_INITIAL) != 0) {
+ if (kex->server) {
+ kex->ext_info_c = kexalgs_contains(peer, "ext-info-c");
+ kex->kex_strict = kexalgs_contains(peer,
+ "kex-strict-c-v00@openssh.com");
+ } else {
+ kex->kex_strict = kexalgs_contains(peer,
+ "kex-strict-s-v00@openssh.com");
+ }
+ if (kex->kex_strict) {
+ debug3("will use strict KEX ordering");
+ if (seq != 0)
+ ssh_packet_disconnect(ssh,
+ "strict KEX violation: "
+ "KEXINIT was not the first packet");
+ }
}
/* Algorithm Negotiation */
Index: openssh-8.4p1/kex.h
===================================================================
--- openssh-8.4p1.orig/kex.h
+++ openssh-8.4p1/kex.h
@@ -154,6 +154,7 @@ struct kex {
u_int kex_type;
char *server_sig_algs;
int ext_info_c;
+ int kex_strict;
struct sshbuf *my;
struct sshbuf *peer;
struct sshbuf *client_version;
Index: openssh-8.4p1/packet.c
===================================================================
--- openssh-8.4p1.orig/packet.c
+++ openssh-8.4p1/packet.c
@@ -1255,6 +1255,11 @@ ssh_packet_send2_wrapped(struct ssh *ssh
state->p_send.bytes += len;
sshbuf_reset(state->outgoing_packet);
+ if (type == SSH2_MSG_NEWKEYS && ssh->kex->kex_strict) {
+ debug("resetting send seqnr %u", state->p_send.seqnr);
+ state->p_send.seqnr = 0;
+ }
+
if (type == SSH2_MSG_NEWKEYS)
r = ssh_set_newkeys(ssh, MODE_OUT);
else if (type == SSH2_MSG_USERAUTH_SUCCESS && state->server_side)
@@ -1388,8 +1393,7 @@ ssh_packet_read_seqnr(struct ssh *ssh, u
/* Stay in the loop until we have received a complete packet. */
for (;;) {
/* Try to read a packet from the buffer. */
- r = ssh_packet_read_poll_seqnr(ssh, typep, seqnr_p);
- if (r != 0)
+ if ((r = ssh_packet_read_poll_seqnr(ssh, typep, seqnr_p)) != 0)
break;
/* If we got a packet, return it. */
if (*typep != SSH_MSG_NONE)
@@ -1677,6 +1681,7 @@ ssh_packet_read_poll2(struct ssh *ssh, u
if ((r = sshbuf_consume(state->input, mac->mac_len)) != 0)
goto out;
}
+
if (seqnr_p != NULL)
*seqnr_p = state->p_read.seqnr;
if (++state->p_read.seqnr == 0)
@@ -1746,6 +1751,10 @@ ssh_packet_read_poll2(struct ssh *ssh, u
#endif
/* reset for next packet */
state->packlen = 0;
+ if (*typep == SSH2_MSG_NEWKEYS && ssh->kex->kex_strict) {
+ debug("resetting read seqnr %u", state->p_read.seqnr);
+ state->p_read.seqnr = 0;
+ }
/* do we need to rekey? */
if (ssh_packet_need_rekeying(ssh, 0)) {
@@ -1770,10 +1779,39 @@ ssh_packet_read_poll_seqnr(struct ssh *s
r = ssh_packet_read_poll2(ssh, typep, seqnr_p);
if (r != 0)
return r;
- if (*typep) {
- state->keep_alive_timeouts = 0;
- DBG(debug("received packet type %d", *typep));
+ if (*typep == 0) {
+ /* no message ready */
+ return 0;
+ }
+ state->keep_alive_timeouts = 0;
+ DBG(debug("received packet type %d", *typep));
+
+ /* Always process disconnect messages */
+ if (*typep == SSH2_MSG_DISCONNECT) {
+ if ((r = sshpkt_get_u32(ssh, &reason)) != 0 ||
+ (r = sshpkt_get_string(ssh, &msg, NULL)) != 0)
+ return r;
+ /* Ignore normal client exit notifications */
+ do_log2(ssh->state->server_side &&
+ reason == SSH2_DISCONNECT_BY_APPLICATION ?
+ SYSLOG_LEVEL_INFO : SYSLOG_LEVEL_ERROR,
+ "Received disconnect from %s port %d:"
+ "%u: %.400s", ssh_remote_ipaddr(ssh),
+ ssh_remote_port(ssh), reason, msg);
+ free(msg);
+ return SSH_ERR_DISCONNECTED;
}
+
+ /*
+ * Do not implicitly handle any messages here during initial
+ * KEX when in strict mode. They will be need to be allowed
+ * explicitly by the KEX dispatch table or they will generate
+ * protocol errors.
+ */
+ if (ssh->kex != NULL &&
+ (ssh->kex->flags & KEX_INITIAL) && ssh->kex->kex_strict)
+ return 0;
+ /* Implicitly handle transport-level messages */
switch (*typep) {
case SSH2_MSG_IGNORE:
debug3("Received SSH2_MSG_IGNORE");
@@ -1788,19 +1826,6 @@ ssh_packet_read_poll_seqnr(struct ssh *s
debug("Remote: %.900s", msg);
free(msg);
break;
- case SSH2_MSG_DISCONNECT:
- if ((r = sshpkt_get_u32(ssh, &reason)) != 0 ||
- (r = sshpkt_get_string(ssh, &msg, NULL)) != 0)
- return r;
- /* Ignore normal client exit notifications */
- do_log2(ssh->state->server_side &&
- reason == SSH2_DISCONNECT_BY_APPLICATION ?
- SYSLOG_LEVEL_INFO : SYSLOG_LEVEL_ERROR,
- "Received disconnect from %s port %d:"
- "%u: %.400s", ssh_remote_ipaddr(ssh),
- ssh_remote_port(ssh), reason, msg);
- free(msg);
- return SSH_ERR_DISCONNECTED;
case SSH2_MSG_UNIMPLEMENTED:
if ((r = sshpkt_get_u32(ssh, &seqnr)) != 0)
return r;
@@ -2346,6 +2371,7 @@ kex_to_blob(struct sshbuf *m, struct kex
(r = sshbuf_put_u32(m, kex->hostkey_type)) != 0 ||
(r = sshbuf_put_u32(m, kex->hostkey_nid)) != 0 ||
(r = sshbuf_put_u32(m, kex->kex_type)) != 0 ||
+ (r = sshbuf_put_u32(m, kex->kex_strict)) != 0 ||
(r = sshbuf_put_stringb(m, kex->my)) != 0 ||
(r = sshbuf_put_stringb(m, kex->peer)) != 0 ||
(r = sshbuf_put_stringb(m, kex->client_version)) != 0 ||
@@ -2511,6 +2537,7 @@ kex_from_blob(struct sshbuf *m, struct k
(r = sshbuf_get_u32(m, (u_int *)&kex->hostkey_type)) != 0 ||
(r = sshbuf_get_u32(m, (u_int *)&kex->hostkey_nid)) != 0 ||
(r = sshbuf_get_u32(m, &kex->kex_type)) != 0 ||
+ (r = sshbuf_get_u32(m, &kex->kex_strict)) != 0 ||
(r = sshbuf_get_stringb(m, kex->my)) != 0 ||
(r = sshbuf_get_stringb(m, kex->peer)) != 0 ||
(r = sshbuf_get_stringb(m, kex->client_version)) != 0 ||
@@ -2847,6 +2874,7 @@ sshpkt_disconnect(struct ssh *ssh, const
vsnprintf(buf, sizeof(buf), fmt, args);
va_end(args);
+ debug2("sending SSH2_MSG_DISCONNECT: %s", buf);
if ((r = sshpkt_start(ssh, SSH2_MSG_DISCONNECT)) != 0 ||
(r = sshpkt_put_u32(ssh, SSH2_DISCONNECT_PROTOCOL_ERROR)) != 0 ||
(r = sshpkt_put_cstring(ssh, buf)) != 0 ||
Index: openssh-8.4p1/sshconnect2.c
===================================================================
--- openssh-8.4p1.orig/sshconnect2.c
+++ openssh-8.4p1/sshconnect2.c
@@ -233,8 +233,12 @@ ssh_kex2(struct ssh *ssh, char *host, st
fatal("%s: kex_assemble_namelist", __func__);
free(all_key);
- if ((s = kex_names_cat(options.kex_algorithms, "ext-info-c")) == NULL)
- fatal("%s: kex_names_cat", __func__);
+ /* Append EXT_INFO signalling to KexAlgorithms */
+ if ((s = kex_names_cat(options.kex_algorithms, ssh->kex->server ?
+ "kex-strict-s-v00@openssh.com" :
+ "ext-info-c,kex-strict-c-v00@openssh.com")) == NULL)
+ fatal("kex_names_cat");
+
myproposal[PROPOSAL_KEX_ALGS] = compat_kex_proposal(s);
myproposal[PROPOSAL_ENC_ALGS_CTOS] =
compat_cipher_proposal(options.ciphers);
@@ -417,7 +421,6 @@ struct cauthmethod {
};
static int input_userauth_service_accept(int, u_int32_t, struct ssh *);
-static int input_userauth_ext_info(int, u_int32_t, struct ssh *);
static int input_userauth_success(int, u_int32_t, struct ssh *);
static int input_userauth_failure(int, u_int32_t, struct ssh *);
static int input_userauth_banner(int, u_int32_t, struct ssh *);
@@ -540,7 +543,7 @@ ssh_userauth2(struct ssh *ssh, const cha
ssh->authctxt = &authctxt;
ssh_dispatch_init(ssh, &input_userauth_error);
- ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, &input_userauth_ext_info);
+ ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, kex_input_ext_info);
ssh_dispatch_set(ssh, SSH2_MSG_SERVICE_ACCEPT, &input_userauth_service_accept);
ssh_dispatch_run_fatal(ssh, DISPATCH_BLOCK, &authctxt.success); /* loop until success */
pubkey_cleanup(ssh);
@@ -585,13 +588,6 @@ input_userauth_service_accept(int type,
return r;
}
-/* ARGSUSED */
-static int
-input_userauth_ext_info(int type, u_int32_t seqnr, struct ssh *ssh)
-{
- return kex_input_ext_info(type, seqnr, ssh);
-}
-
void
userauth(struct ssh *ssh, char *authlist)
{
@@ -673,6 +669,7 @@ input_userauth_success(int type, u_int32
free(authctxt->methoddata);
authctxt->methoddata = NULL;
authctxt->success = 1; /* break out */
+ ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, dispatch_protocol_error);
return 0;
}
Index: openssh-8.4p1/sshd.c
===================================================================
--- openssh-8.4p1.orig/sshd.c
+++ openssh-8.4p1/sshd.c
@@ -2371,9 +2371,19 @@ do_ssh2_kex(struct ssh *ssh)
char *myproposal[PROPOSAL_MAX] = { KEX_SERVER };
struct kex *kex;
int r;
+ char *s;
- myproposal[PROPOSAL_KEX_ALGS] = compat_kex_proposal(
- options.kex_algorithms);
+ /* Append EXT_INFO signalling to KexAlgorithms */
+ if (options.kex_algorithms == NULL)
+ s = strdup("kex-strict-s-v00@openssh.com");
+ else
+ s = kex_names_cat(options.kex_algorithms,
+ "kex-strict-s-v00@openssh.com");
+
+ if (s == NULL)
+ fatal("%s: kex_names_cat", __func__);
+
+ myproposal[PROPOSAL_KEX_ALGS] = compat_kex_proposal(s);
myproposal[PROPOSAL_ENC_ALGS_CTOS] = compat_cipher_proposal(
options.ciphers);
myproposal[PROPOSAL_ENC_ALGS_STOC] = compat_cipher_proposal(
