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File _service:tar_scm:backport-0011-CVE-2023-48795-client-side-mitigation.patch of Package libssh
From 4cef5e965a46e9271aed62631b152e4bd23c1e3c Mon Sep 17 00:00:00 2001 From: Aris Adamantiadis <aris@0xbadc0de.be> Date: Tue, 12 Dec 2023 23:09:57 +0100 Subject: [PATCH 11/20] CVE-2023-48795: client side mitigation Signed-off-by: Aris Adamantiadis <aris@0xbadc0de.be> Signed-off-by: Jakub Jelen <jjelen@redhat.com> Reviewed-by: Andreas Schneider <asn@cryptomilk.org> --- include/libssh/packet.h | 1 + include/libssh/session.h | 6 +++++ src/curve25519.c | 19 +++---------- src/dh-gex.c | 7 +---- src/dh.c | 17 +++--------- src/ecdh.c | 8 +----- src/ecdh_crypto.c | 12 +++------ src/ecdh_gcrypt.c | 10 +++---- src/ecdh_mbedcrypto.c | 11 +++----- src/kex.c | 34 +++++++++++++++++++---- src/packet.c | 58 ++++++++++++++++++++++++++++++++++++++++ src/packet_cb.c | 12 +++++++++ 12 files changed, 126 insertions(+), 69 deletions(-) diff --git a/include/libssh/packet.h b/include/libssh/packet.h index 7f10a709..f0c8cb20 100644 --- a/include/libssh/packet.h +++ b/include/libssh/packet.h @@ -67,6 +67,7 @@ SSH_PACKET_CALLBACK(ssh_packet_ext_info); SSH_PACKET_CALLBACK(ssh_packet_kexdh_init); #endif +int ssh_packet_send_newkeys(ssh_session session); int ssh_packet_send_unimplemented(ssh_session session, uint32_t seqnum); int ssh_packet_parse_type(ssh_session session); //int packet_flush(ssh_session session, int enforce_blocking); diff --git a/include/libssh/session.h b/include/libssh/session.h index eb14e97a..97936195 100644 --- a/include/libssh/session.h +++ b/include/libssh/session.h @@ -81,6 +81,12 @@ enum ssh_pending_call_e { * sending it twice during key exchange to simplify the state machine. */ #define SSH_SESSION_FLAG_KEXINIT_SENT 4 +/* The current SSH2 session implements the "strict KEX" feature and should behave + * differently on SSH2_MSG_NEWKEYS. */ +#define SSH_SESSION_FLAG_KEX_STRICT 0x0010 +/* Unexpected packets have been sent while the session was still unencrypted */ +#define SSH_SESSION_FLAG_KEX_TAINTED 0x0020 + /* codes to use with ssh_handle_packets*() */ /* Infinite timeout */ #define SSH_TIMEOUT_INFINITE -1 diff --git a/src/curve25519.c b/src/curve25519.c index 66291b5f..4aeb4756 100644 --- a/src/curve25519.c +++ b/src/curve25519.c @@ -335,16 +335,10 @@ static SSH_PACKET_CALLBACK(ssh_packet_client_curve25519_reply){ } /* Send the MSG_NEWKEYS */ - if (ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS) < 0) { - goto error; - } - - rc=ssh_packet_send(session); + rc = ssh_packet_send_newkeys(session); if (rc == SSH_ERROR) { goto error; } - - SSH_LOG(SSH_LOG_PROTOCOL, "SSH_MSG_NEWKEYS sent"); session->dh_handshake_state = DH_STATE_NEWKEYS_SENT; return SSH_PACKET_USED; @@ -502,18 +496,13 @@ static SSH_PACKET_CALLBACK(ssh_packet_server_curve25519_init){ return SSH_ERROR; } - /* Send the MSG_NEWKEYS */ - rc = ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS); - if (rc < 0) { - goto error; - } - session->dh_handshake_state = DH_STATE_NEWKEYS_SENT; - rc = ssh_packet_send(session); + + /* Send the MSG_NEWKEYS */ + rc = ssh_packet_send_newkeys(session); if (rc == SSH_ERROR) { goto error; } - SSH_LOG(SSH_LOG_PROTOCOL, "SSH_MSG_NEWKEYS sent"); return SSH_PACKET_USED; error: diff --git a/src/dh-gex.c b/src/dh-gex.c index 91617081..642a88ae 100644 --- a/src/dh-gex.c +++ b/src/dh-gex.c @@ -297,15 +297,10 @@ static SSH_PACKET_CALLBACK(ssh_packet_client_dhgex_reply) } /* Send the MSG_NEWKEYS */ - if (ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS) < 0) { - goto error; - } - - rc = ssh_packet_send(session); + rc = ssh_packet_send_newkeys(session); if (rc == SSH_ERROR) { goto error; } - SSH_LOG(SSH_LOG_PROTOCOL, "SSH_MSG_NEWKEYS sent"); session->dh_handshake_state = DH_STATE_NEWKEYS_SENT; return SSH_PACKET_USED; diff --git a/src/dh.c b/src/dh.c index 011d97b3..e19e43d1 100644 --- a/src/dh.c +++ b/src/dh.c @@ -398,16 +398,10 @@ SSH_PACKET_CALLBACK(ssh_packet_client_dh_reply){ } /* Send the MSG_NEWKEYS */ - if (ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS) < 0) { - goto error; - } - - rc=ssh_packet_send(session); + rc = ssh_packet_send_newkeys(session); if (rc == SSH_ERROR) { goto error; } - - SSH_LOG(SSH_LOG_PROTOCOL, "SSH_MSG_NEWKEYS sent"); session->dh_handshake_state = DH_STATE_NEWKEYS_SENT; return SSH_PACKET_USED; error: @@ -551,15 +545,12 @@ int ssh_server_dh_process_init(ssh_session session, ssh_buffer packet) } SSH_LOG(SSH_LOG_DEBUG, "Sent KEX_DH_[GEX]_REPLY"); - if (ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS) < 0) { - ssh_buffer_reinit(session->out_buffer); - goto error; - } session->dh_handshake_state=DH_STATE_NEWKEYS_SENT; - if (ssh_packet_send(session) == SSH_ERROR) { + /* Send the MSG_NEWKEYS */ + rc = ssh_packet_send_newkeys(session); + if (rc == SSH_ERROR) { goto error; } - SSH_LOG(SSH_LOG_PACKET, "SSH_MSG_NEWKEYS sent"); return SSH_OK; error: diff --git a/src/ecdh.c b/src/ecdh.c index e5b11ba9..af80beec 100644 --- a/src/ecdh.c +++ b/src/ecdh.c @@ -93,16 +93,10 @@ SSH_PACKET_CALLBACK(ssh_packet_client_ecdh_reply){ } /* Send the MSG_NEWKEYS */ - if (ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS) < 0) { - goto error; - } - - rc=ssh_packet_send(session); + rc = ssh_packet_send_newkeys(session); if (rc == SSH_ERROR) { goto error; } - - SSH_LOG(SSH_LOG_PROTOCOL, "SSH_MSG_NEWKEYS sent"); session->dh_handshake_state = DH_STATE_NEWKEYS_SENT; return SSH_PACKET_USED; diff --git a/src/ecdh_crypto.c b/src/ecdh_crypto.c index 51084b7a..069b1372 100644 --- a/src/ecdh_crypto.c +++ b/src/ecdh_crypto.c @@ -619,18 +619,12 @@ SSH_PACKET_CALLBACK(ssh_packet_server_ecdh_init){ goto error; } - /* Send the MSG_NEWKEYS */ - rc = ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS); - if (rc < 0) { - goto error; - } - session->dh_handshake_state = DH_STATE_NEWKEYS_SENT; - rc = ssh_packet_send(session); - if (rc == SSH_ERROR){ + /* Send the MSG_NEWKEYS */ + rc = ssh_packet_send_newkeys(session); + if (rc == SSH_ERROR) { goto error; } - SSH_LOG(SSH_LOG_PROTOCOL, "SSH_MSG_NEWKEYS sent"); return SSH_PACKET_USED; error: diff --git a/src/ecdh_gcrypt.c b/src/ecdh_gcrypt.c index 235f2904..3d9d426f 100644 --- a/src/ecdh_gcrypt.c +++ b/src/ecdh_gcrypt.c @@ -372,17 +372,13 @@ SSH_PACKET_CALLBACK(ssh_packet_server_ecdh_init){ goto out; } - + session->dh_handshake_state = DH_STATE_NEWKEYS_SENT; /* Send the MSG_NEWKEYS */ - rc = ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS); - if (rc != SSH_OK) { + rc = ssh_packet_send_newkeys(session); + if (rc == SSH_ERROR) { goto out; } - session->dh_handshake_state = DH_STATE_NEWKEYS_SENT; - rc = ssh_packet_send(session); - SSH_LOG(SSH_LOG_PROTOCOL, "SSH_MSG_NEWKEYS sent"); - out: gcry_sexp_release(param); gcry_sexp_release(key); diff --git a/src/ecdh_mbedcrypto.c b/src/ecdh_mbedcrypto.c index cfe017a0..dda73922 100644 --- a/src/ecdh_mbedcrypto.c +++ b/src/ecdh_mbedcrypto.c @@ -318,16 +318,13 @@ SSH_PACKET_CALLBACK(ssh_packet_server_ecdh_init){ goto out; } - rc = ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS); - if (rc < 0) { - rc = SSH_ERROR; + session->dh_handshake_state = DH_STATE_NEWKEYS_SENT; + /* Send the MSG_NEWKEYS */ + rc = ssh_packet_send_newkeys(session); + if (rc == SSH_ERROR) { goto out; } - session->dh_handshake_state = DH_STATE_NEWKEYS_SENT; - rc = ssh_packet_send(session); - SSH_LOG(SSH_LOG_PROTOCOL, "SSH_MSG_NEWKEYS sent"); - out: mbedtls_ecp_group_free(&grp); if (rc == SSH_ERROR) { diff --git a/src/kex.c b/src/kex.c index b9455d2d..3818297b 100644 --- a/src/kex.c +++ b/src/kex.c @@ -188,6 +188,9 @@ /* RFC 8308 */ #define KEX_EXTENSION_CLIENT "ext-info-c" +/* Strict kex mitigation against CVE-2023-48795 */ +#define KEX_STRICT_CLIENT "kex-strict-c-v00@openssh.com" +#define KEX_STRICT_SERVER "kex-strict-s-v00@openssh.com" /* Allowed algorithms in FIPS mode */ #define FIPS_ALLOWED_CIPHERS "aes256-gcm@openssh.com,"\ @@ -516,6 +519,27 @@ SSH_PACKET_CALLBACK(ssh_packet_kexinit) session->first_kex_follows_guess_wrong ? "wrong" : "right"); } + /* + * handle the "strict KEX" feature. If supported by peer, then set up the + * flag and verify packet sequence numbers. + */ + if (server_kex) { + ok = ssh_match_group(crypto->client_kex.methods[SSH_KEX], + KEX_STRICT_CLIENT); + if (ok) { + SSH_LOG(SSH_LOG_DEBUG, "Client supports strict kex, enabling."); + session->flags |= SSH_SESSION_FLAG_KEX_STRICT; + } + } else { + /* client kex */ + ok = ssh_match_group(crypto->server_kex.methods[SSH_KEX], + KEX_STRICT_SERVER); + if (ok) { + SSH_LOG(SSH_LOG_DEBUG, "Server supports strict kex, enabling."); + session->flags |= SSH_SESSION_FLAG_KEX_STRICT; + } + } + if (server_kex) { /* * If client sent a ext-info-c message in the kex list, it supports @@ -792,21 +816,21 @@ int ssh_set_client_kex(ssh_session session) return SSH_OK; } - /* Here we append ext-info-c to the list of kex algorithms */ + /* Here we append ext-info-c and kex-strict-c-v00@openssh.com to the list of kex algorithms */ kex = client->methods[SSH_KEX]; len = strlen(kex); - if (len + strlen(KEX_EXTENSION_CLIENT) + 2 < len) { + /* Comma, comma, nul byte */ + kex_len = len + 1 + strlen(KEX_EXTENSION_CLIENT) + 1 + strlen(KEX_STRICT_CLIENT ) + 1; + if (kex_len >= MAX_PACKET_LEN) { /* Overflow */ return SSH_ERROR; } - kex_len = len + strlen(KEX_EXTENSION_CLIENT) + 2; /* comma, NULL */ kex_tmp = realloc(kex, kex_len); if (kex_tmp == NULL) { - free(kex); ssh_set_error_oom(session); return SSH_ERROR; } - snprintf(kex_tmp + len, kex_len - len, ",%s", KEX_EXTENSION_CLIENT); + snprintf(kex_tmp + len, kex_len - len, ",%s,%s", KEX_EXTENSION_CLIENT, KEX_STRICT_CLIENT); client->methods[SSH_KEX] = kex_tmp; return SSH_OK; diff --git a/src/packet.c b/src/packet.c index eb7eb42a..ea73f9ad 100644 --- a/src/packet.c +++ b/src/packet.c @@ -1314,6 +1314,19 @@ ssh_packet_socket_callback(const void *data, size_t receivedlen, void *user) } #endif /* WITH_ZLIB */ payloadsize = ssh_buffer_get_len(session->in_buffer); + if (session->recv_seq == UINT32_MAX) { + /* Overflowing sequence numbers is always fishy */ + if (crypto == NULL) { + /* don't allow sequence number overflow when unencrypted */ + ssh_set_error(session, + SSH_FATAL, + "Incoming sequence number overflow"); + goto error; + } else { + SSH_LOG(SSH_LOG_WARNING, + "Incoming sequence number overflow"); + } + } session->recv_seq++; if (crypto != NULL) { struct ssh_cipher_struct *cipher = NULL; @@ -1338,7 +1351,19 @@ ssh_packet_socket_callback(const void *data, size_t receivedlen, void *user) "comp=%" PRIu32 ",payload=%" PRIu32 "]", session->in_packet.type, packet_len, padding, compsize, payloadsize); + if (crypto == NULL) { + /* In strict kex, only a few packets are allowed. Taint the session + * if we received packets that are normally allowed but to be + * refused if we are in strict kex when KEX is over. + */ + uint8_t type = session->in_packet.type; + if (type != SSH2_MSG_KEXINIT && type != SSH2_MSG_NEWKEYS && + (type < SSH2_MSG_KEXDH_INIT || + type > SSH2_MSG_KEX_DH_GEX_REQUEST)) { + session->flags |= SSH_SESSION_FLAG_KEX_TAINTED; + } + } /* Check if the packet is expected */ filter_result = ssh_packet_incoming_filter(session); @@ -1354,6 +1379,9 @@ ssh_packet_socket_callback(const void *data, size_t receivedlen, void *user) session->in_packet.type); goto error; case SSH_PACKET_UNKNOWN: + if (crypto == NULL) { + session->flags |= SSH_SESSION_FLAG_KEX_TAINTED; + } ssh_packet_send_unimplemented(session, session->recv_seq - 1); break; } @@ -1529,7 +1557,33 @@ void ssh_packet_process(ssh_session session, uint8_t type) SSH_LOG(SSH_LOG_RARE, "Failed to send unimplemented: %s", ssh_get_error(session)); } + if (session->current_crypto == NULL) { + session->flags |= SSH_SESSION_FLAG_KEX_TAINTED; + } + } +} + +/** @internal + * @brief sends a SSH_MSG_NEWKEYS when enabling the new negotiated ciphers + * @param session the SSH session + * @return SSH_ERROR on error, else SSH_OK + */ +int ssh_packet_send_newkeys(ssh_session session) +{ + int rc; + + /* Send the MSG_NEWKEYS */ + rc = ssh_buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS); + if (rc < 0) { + return rc; } + + rc = ssh_packet_send(session); + if (rc == SSH_ERROR) { + return rc; + } + SSH_LOG(SSH_LOG_DEBUG, "SSH_MSG_NEWKEYS sent"); + return rc; } /** @internal @@ -1842,6 +1896,10 @@ int ssh_packet_send(ssh_session session) if (rc == SSH_OK && type == SSH2_MSG_NEWKEYS) { struct ssh_iterator *it; + if (session->flags & SSH_SESSION_FLAG_KEX_STRICT) { + /* reset packet sequence number when running in strict kex mode */ + session->send_seq = 0; + } for (it = ssh_list_get_iterator(session->out_queue); it != NULL; it = ssh_list_get_iterator(session->out_queue)) { diff --git a/src/packet_cb.c b/src/packet_cb.c index 0ecf8771..2f364c26 100644 --- a/src/packet_cb.c +++ b/src/packet_cb.c @@ -115,6 +115,18 @@ SSH_PACKET_CALLBACK(ssh_packet_newkeys){ goto error; } + if (session->flags & SSH_SESSION_FLAG_KEX_STRICT) { + /* reset packet sequence number when running in strict kex mode */ + session->recv_seq = 0; + /* Check that we aren't tainted */ + if (session->flags & SSH_SESSION_FLAG_KEX_TAINTED) { + ssh_set_error(session, + SSH_FATAL, + "Received unexpected packets in strict KEX mode."); + goto error; + } + } + if(session->server){ /* server things are done in server.c */ session->dh_handshake_state=DH_STATE_FINISHED; -- 2.33.0
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