From: Steffan Karger Date: Tue, 9 May 2017 19:30:07 +0000 (+0200) Subject: Drop packets instead of assert out if packet id rolls over (CVE-2017-7479) X-Git-Tag: v2.3.15~2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b727643cdf4e078f132a90e1c474a879a5760578;p=thirdparty%2Fopenvpn.git Drop packets instead of assert out if packet id rolls over (CVE-2017-7479) Previously, if a mode was selected where packet ids are not allowed to roll over, but renegotiation does not succeed for some reason (e.g. no password entered in time, certificate expired or a malicious peer that refuses the renegotiaion on purpose) we would continue to use the old keys. Until the packet ID would roll over and we would ASSERT() out. Given that this can be triggered on purpose by an authenticated peer, this is a fix for an authenticated remote DoS vulnerability. An attack is rather inefficient though; a peer would need to get us to send 2^32 packets (min-size packet is IP+UDP+OPCODE+PID+TAG (no payload), results in (20+8+1+4+16)*2^32 bytes, or approx. 196 GB). This is a fix for finding 5.2 from the OSTIF / Quarkslab audit. CVE: 2017-7479 Signed-off-by: Steffan Karger Acked-by: Gert Doering Acked-by: David Sommerseth Message-Id: <1494358209-4568-1-git-send-email-steffan.karger@fox-it.com> URL: http://www.mail-archive.com/search?l=mid&q=1494358209-4568-1-git-send-email-steffan.karger@fox-it.com Signed-off-by: David Sommerseth --- diff --git a/Changes.rst b/Changes.rst index 1c0154c46..183e9fa4a 100644 --- a/Changes.rst +++ b/Changes.rst @@ -104,6 +104,16 @@ Behavioral changes - Do not randomize resolving of IP addresses in getaddr() +Version 2.3.15 +============== + +Security fixes +-------------- +- Fix an authenticated remote DoS vulnerability that could be triggered by + causing a packet id roll over. An attack is rather inefficient; a peer + would need to get us to send at least about 196 GB of data. + (OSTIF/Quarkslab audit finding 5.2, CVE-2017-7479) + Version 2.3.14 ============== diff --git a/src/openvpn/crypto.c b/src/openvpn/crypto.c index 6fc97ddc9..9d96f1247 100644 --- a/src/openvpn/crypto.c +++ b/src/openvpn/crypto.c @@ -110,9 +110,11 @@ openvpn_encrypt (struct buffer *buf, struct buffer work, prng_bytes (iv_buf, iv_size); /* Put packet ID in plaintext buffer or IV, depending on cipher mode */ - if (opt->packet_id) + if (opt->packet_id + && !packet_id_write (&opt->packet_id->send, buf, BOOL_CAST (opt->flags & CO_PACKET_ID_LONG_FORM), true)) { - ASSERT (packet_id_write (&opt->packet_id->send, buf, BOOL_CAST (opt->flags & CO_PACKET_ID_LONG_FORM), true)); + msg (D_CRYPT_ERRORS, "ENCRYPT ERROR: packet ID roll over"); + goto err; } } else if (cipher_kt_mode_ofb_cfb(cipher_kt)) @@ -123,7 +125,11 @@ openvpn_encrypt (struct buffer *buf, struct buffer work, ASSERT (opt->packet_id); /* for this mode. */ buf_set_write (&b, iv_buf, iv_size); - ASSERT (packet_id_write (&opt->packet_id->send, &b, true, false)); + if (!packet_id_write (&opt->packet_id->send, &b, true, false)) + { + msg (D_CRYPT_ERRORS, "ENCRYPT ERROR: packet ID roll over"); + goto err; + } } else /* We only support CBC, CFB, or OFB modes right now */ { @@ -182,9 +188,11 @@ openvpn_encrypt (struct buffer *buf, struct buffer work, } else /* No Encryption */ { - if (opt->packet_id) + if (opt->packet_id + && !packet_id_write (&opt->packet_id->send, buf, BOOL_CAST (opt->flags & CO_PACKET_ID_LONG_FORM), true)) { - ASSERT (packet_id_write (&opt->packet_id->send, buf, BOOL_CAST (opt->flags & CO_PACKET_ID_LONG_FORM), true)); + msg (D_CRYPT_ERRORS, "ENCRYPT ERROR: packet ID roll over"); + goto err; } work = *buf; } diff --git a/src/openvpn/packet_id.c b/src/openvpn/packet_id.c index c637be66d..9af74a1e7 100644 --- a/src/openvpn/packet_id.c +++ b/src/openvpn/packet_id.c @@ -294,27 +294,37 @@ packet_id_read (struct packet_id_net *pin, struct buffer *buf, bool long_form) return true; } -static void +static bool packet_id_send_update(struct packet_id_send *p, bool long_form) { if (!p->time) { p->time = now; } - p->id++; - if (!p->id) + if (p->id == PACKET_ID_MAX) { - ASSERT(long_form); + /* Packet ID only allowed to roll over if using long form and time has + * moved forward since last roll over. + */ + if (!long_form || now <= p->time) + { + return false; + } p->time = now; - p->id = 1; + p->id = 0; } + p->id++; + return true; } bool packet_id_write (struct packet_id_send *p, struct buffer *buf, bool long_form, bool prepend) { - packet_id_send_update(p, long_form); + if (!packet_id_send_update(p, long_form)) + { + return false; + } const packet_id_type net_id = htonpid(p->id); const net_time_t net_time = htontime(p->time); diff --git a/src/openvpn/packet_id.h b/src/openvpn/packet_id.h index f6fa9bd1e..bfdfb771b 100644 --- a/src/openvpn/packet_id.h +++ b/src/openvpn/packet_id.h @@ -50,6 +50,7 @@ * to for network transmission. */ typedef uint32_t packet_id_type; +#define PACKET_ID_MAX UINT32_MAX typedef uint32_t net_time_t; /* diff --git a/tests/unit_tests/openvpn/test_packet_id.c b/tests/unit_tests/openvpn/test_packet_id.c index 3662e17f2..1ab3fd850 100644 --- a/tests/unit_tests/openvpn/test_packet_id.c +++ b/tests/unit_tests/openvpn/test_packet_id.c @@ -130,8 +130,7 @@ test_packet_id_write_short_wrap(void **state) struct test_packet_id_write_data *data = *state; data->pis.id = ~0; - expect_assert_failure( - packet_id_write(&data->pis, &data->test_buf, false, false)); + assert_false(packet_id_write(&data->pis, &data->test_buf, false, false)); } static void @@ -140,8 +139,16 @@ test_packet_id_write_long_wrap(void **state) struct test_packet_id_write_data *data = *state; data->pis.id = ~0; + data->pis.time = 5006; + + /* Write fails if time did not change */ + now = 5006; + assert_false(packet_id_write(&data->pis, &data->test_buf, true, false)); + + /* Write succeeds if time moved forward */ now = 5010; assert_true(packet_id_write(&data->pis, &data->test_buf, true, false)); + assert(data->pis.id == 1); assert(data->pis.time == now); assert_true(data->test_buf_data.buf_id == htonl(1));