diff options
Diffstat (limited to '')
| -rw-r--r-- | debian/patches/CVE-2023-48795.patch | 468 |
1 files changed, 468 insertions, 0 deletions
diff --git a/debian/patches/CVE-2023-48795.patch b/debian/patches/CVE-2023-48795.patch new file mode 100644 index 0000000..ef4eca1 --- /dev/null +++ b/debian/patches/CVE-2023-48795.patch @@ -0,0 +1,468 @@ +From 9148d0a8031d89f53f045b63ac3a709611d94778 Mon Sep 17 00:00:00 2001 +From: "djm@openbsd.org" <djm@openbsd.org> +Date: Mon, 18 Dec 2023 14:45:17 +0000 +Subject: upstream: implement "strict key exchange" in ssh and sshd + +This adds a protocol extension to improve the integrity of the SSH +transport protocol, particular in and around the initial key exchange +(KEX) phase. + +Full details of the extension are in the PROTOCOL file. + +with markus@ + +OpenBSD-Commit-ID: 2a66ac962f0a630d7945fee54004ed9e9c439f14 + +Origin: backport, https://anongit.mindrot.org/openssh.git/commit/?id=1edb00c58f8a6875fad6a497aa2bacf37f9e6cd5 +Last-Update: 2023-12-19 + +Patch-Name: CVE-2023-48795.patch +--- + PROTOCOL | 26 +++++++++++++++++ + kex.c | 72 +++++++++++++++++++++++++++++++---------------- + kex.h | 1 + + packet.c | 78 ++++++++++++++++++++++++++++++++++++++------------- + sshconnect2.c | 14 +++------ + sshd.c | 9 ++++-- + 6 files changed, 143 insertions(+), 57 deletions(-) + +diff --git a/PROTOCOL b/PROTOCOL +index 27804d0ca..ad611a01a 100644 +--- a/PROTOCOL ++++ b/PROTOCOL +@@ -104,6 +104,32 @@ http://git.libssh.org/users/aris/libssh.git/plain/doc/curve25519-sha256@libssh.o + + This is identical to curve25519-sha256 as later published in RFC8731. + ++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 ++RFC8308 ext-info feature: by including a additional algorithm in the ++initiial 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". These pseudo-algorithms ++are only valid in the initial SSH2_MSG_KEXINIT and MUST be ignored ++if they are present in subsequent SSH2_MSG_KEXINIT packets. ++ ++When an 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. ++ Unexpected packets for the purpose of strict KEX include messages ++ that are otherwise valid at any time during the connection such as ++ SSH2_MSG_DEBUG and SSH2_MSG_IGNORE. ++b) After sending or receiving a SSH2_MSG_NEWKEYS message, reset the ++ packet sequence number to zero. This behaviour persists for the ++ duration of the connection (i.e. not just the first ++ SSH2_MSG_NEWKEYS). ++ + 2. Connection protocol changes + + 2.1. connection: Channel write close extension "eow@openssh.com" +diff --git a/kex.c b/kex.c +index e7b7316c7..0b4fc4767 100644 +--- a/kex.c ++++ b/kex.c +@@ -68,7 +68,7 @@ + #endif + + /* 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 * const proposal_names[PROPOSAL_MAX] = { +@@ -209,6 +209,18 @@ 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; ++} ++ + /* + * Concatenate algorithm names, avoiding duplicates in the process. + * Caller must free returned string. +@@ -216,7 +228,7 @@ 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') +@@ -233,10 +245,8 @@ kex_names_cat(const char *a, const char *b) + } + 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); +@@ -467,7 +477,12 @@ kex_protocol_error(int type, u_int32_t seq, struct ssh *ssh) + { + 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_f("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) +@@ -542,6 +557,11 @@ kex_input_ext_info(int type, u_int32_t seq, struct ssh *ssh) + 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; +@@ -657,7 +677,7 @@ kex_input_kexinit(int type, u_int32_t seq, struct ssh *ssh) + error_f("no kex"); + 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; +@@ -693,7 +713,7 @@ kex_input_kexinit(int type, u_int32_t seq, struct ssh *ssh) + 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) +@@ -960,20 +980,14 @@ proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX]) + return (1); + } + +-/* returns non-zero if proposal contains any algorithm from algs */ + static int +-has_any_alg(const char *proposal, const char *algs) ++kexalgs_contains(char **peer, const char *ext) + { +- char *cp; +- +- if ((cp = match_list(proposal, algs, NULL)) == NULL) +- return 0; +- free(cp); +- return 1; ++ return has_any_alg(peer[PROPOSAL_KEX_ALGS], ext); + } + + 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; +@@ -998,13 +1012,23 @@ 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_f("will use strict KEX ordering"); ++ if (seq != 0) ++ ssh_packet_disconnect(ssh, ++ "strict KEX violation: " ++ "KEXINIT was not the first packet"); ++ } + } + + /* Check whether client supports rsa-sha2 algorithms */ +diff --git a/kex.h b/kex.h +index e356f5ed0..99b47435f 100644 +--- a/kex.h ++++ b/kex.h +@@ -157,6 +157,7 @@ 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; +diff --git a/packet.c b/packet.c +index 3f64d2d32..25553fbb5 100644 +--- a/packet.c ++++ b/packet.c +@@ -1205,8 +1205,13 @@ ssh_packet_send2_wrapped(struct ssh *ssh) + sshbuf_dump(state->output, stderr); + #endif + /* increment sequence number for outgoing packets */ +- if (++state->p_send.seqnr == 0) ++ if (++state->p_send.seqnr == 0) { ++ if ((ssh->kex->flags & KEX_INITIAL) != 0) { ++ ssh_packet_disconnect(ssh, "outgoing sequence number " ++ "wrapped during initial key exchange"); ++ } + logit("outgoing seqnr wraps around"); ++ } + if (++state->p_send.packets == 0) + if (!(ssh->compat & SSH_BUG_NOREKEY)) + return SSH_ERR_NEED_REKEY; +@@ -1214,6 +1219,11 @@ 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_f("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) +@@ -1342,8 +1352,7 @@ ssh_packet_read_seqnr(struct ssh *ssh, u_char *typep, u_int32_t *seqnr_p) + /* 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) +@@ -1627,10 +1636,16 @@ ssh_packet_read_poll2(struct ssh *ssh, u_char *typep, u_int32_t *seqnr_p) + 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) ++ if (++state->p_read.seqnr == 0) { ++ if ((ssh->kex->flags & KEX_INITIAL) != 0) { ++ ssh_packet_disconnect(ssh, "incoming sequence number " ++ "wrapped during initial key exchange"); ++ } + logit("incoming seqnr wraps around"); ++ } + if (++state->p_read.packets == 0) + if (!(ssh->compat & SSH_BUG_NOREKEY)) + return SSH_ERR_NEED_REKEY; +@@ -1696,6 +1711,10 @@ ssh_packet_read_poll2(struct ssh *ssh, u_char *typep, u_int32_t *seqnr_p) + #endif + /* reset for next packet */ + state->packlen = 0; ++ if (*typep == SSH2_MSG_NEWKEYS && ssh->kex->kex_strict) { ++ debug_f("resetting read seqnr %u", state->p_read.seqnr); ++ state->p_read.seqnr = 0; ++ } + + if ((r = ssh_packet_check_rekey(ssh)) != 0) + return r; +@@ -1716,10 +1735,39 @@ ssh_packet_read_poll_seqnr(struct ssh *ssh, u_char *typep, u_int32_t *seqnr_p) + 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"); +@@ -1734,19 +1782,6 @@ ssh_packet_read_poll_seqnr(struct ssh *ssh, u_char *typep, u_int32_t *seqnr_p) + 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; +@@ -2211,6 +2246,7 @@ kex_to_blob(struct sshbuf *m, struct kex *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 || +@@ -2373,6 +2409,7 @@ kex_from_blob(struct sshbuf *m, struct kex **kexp) + (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 || +@@ -2701,6 +2738,7 @@ sshpkt_disconnect(struct ssh *ssh, const char *fmt,...) + vsnprintf(buf, sizeof(buf), fmt, args); + va_end(args); + ++ debug2_f("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 || +diff --git a/sshconnect2.c b/sshconnect2.c +index cb6a94e76..3e5f69470 100644 +--- a/sshconnect2.c ++++ b/sshconnect2.c +@@ -250,7 +250,8 @@ ssh_kex2(struct ssh *ssh, char *host, struct sockaddr *hostaddr, u_short port, + fatal_fr(r, "kex_assemble_namelist"); + free(all_key); + +- if ((s = kex_names_cat(options.kex_algorithms, "ext-info-c")) == NULL) ++ if ((s = kex_names_cat(options.kex_algorithms, ++ "ext-info-c,kex-strict-c-v00@openssh.com")) == NULL) + fatal_f("kex_names_cat"); + myproposal[PROPOSAL_KEX_ALGS] = prop_kex = compat_kex_proposal(ssh, s); + myproposal[PROPOSAL_ENC_ALGS_CTOS] = +@@ -441,7 +442,6 @@ 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 *); +@@ -561,7 +561,7 @@ ssh_userauth2(struct ssh *ssh, const char *local_user, + + 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); +@@ -613,13 +613,6 @@ input_userauth_service_accept(int type, u_int32_t seq, struct ssh *ssh) + 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) + { +@@ -701,6 +694,7 @@ input_userauth_success(int type, u_int32_t seq, struct ssh *ssh) + free(authctxt->methoddata); + authctxt->methoddata = NULL; + authctxt->success = 1; /* break out */ ++ ssh_dispatch_set(ssh, SSH2_MSG_EXT_INFO, dispatch_protocol_error); + return 0; + } + +diff --git a/sshd.c b/sshd.c +index fc22fcb62..dd8fd94a3 100644 +--- a/sshd.c ++++ b/sshd.c +@@ -2471,11 +2471,13 @@ do_ssh2_kex(struct ssh *ssh) + { + char *myproposal[PROPOSAL_MAX] = { KEX_SERVER }; + struct kex *kex; +- char *prop_kex = NULL, *prop_enc = NULL, *prop_hostkey = NULL; ++ char *s, *prop_kex = NULL, *prop_enc = NULL, *prop_hostkey = NULL; + int r; + +- myproposal[PROPOSAL_KEX_ALGS] = prop_kex = compat_kex_proposal(ssh, +- options.kex_algorithms); ++ if ((s = kex_names_cat(options.kex_algorithms, ++ "kex-strict-s-v00@openssh.com")) == NULL) ++ fatal_f("kex_names_cat"); ++ myproposal[PROPOSAL_KEX_ALGS] = prop_kex = compat_kex_proposal(ssh, s); + myproposal[PROPOSAL_ENC_ALGS_CTOS] = + myproposal[PROPOSAL_ENC_ALGS_STOC] = prop_enc = + compat_cipher_proposal(ssh, options.ciphers); +@@ -2583,6 +2585,7 @@ do_ssh2_kex(struct ssh *ssh) + free(prop_kex); + free(prop_enc); + free(prop_hostkey); ++ free(s); + debug("KEX done"); + } + |