From e94a6c0ede623960728415b68650a595e48f5a43 Mon Sep 17 00:00:00 2001 From: Emilia Kasper Date: Wed, 19 Nov 2014 17:01:36 +0100 Subject: [PATCH] Ensure SSL3_FLAGS_CCS_OK (or d1->change_cipher_spec_ok for DTLS) is reset once the ChangeCipherSpec message is received. Previously, the server would set the flag once at SSL3_ST_SR_CERT_VRFY and again at SSL3_ST_SR_FINISHED. This would allow a second CCS to arrive and would corrupt the server state. (Because the first CCS would latch the correct keys and subsequent CCS messages would have to be encrypted, a MitM attacker cannot exploit this, though.) Thanks to Joeri de Ruiter for reporting this issue. Reviewed-by: Matt Caswell --- CHANGES | 10 ++++++++++ ssl/d1_clnt.c | 5 +++-- ssl/d1_srvr.c | 26 +++++++++++++++++++++++--- ssl/dtls1.h | 4 ++++ ssl/s3_clnt.c | 10 +++------- ssl/s3_srvr.c | 40 ++++++++++++++++++++++++++++++++++++---- ssl/ssl3.h | 13 ++++++++++--- ssl/t1_lib.c | 2 +- 8 files changed, 90 insertions(+), 20 deletions(-) diff --git a/CHANGES b/CHANGES index 0d9bd505c3..aa07cc09c6 100644 --- a/CHANGES +++ b/CHANGES @@ -305,6 +305,11 @@ Changes between 1.0.1j and 1.0.2 [xx XXX xxxx] + *) Tighten handling of the ChangeCipherSpec (CCS) message: reject + early CCS messages during renegotiation. (Note that because + renegotiation is encrypted, this early CCS was not exploitable.) + [Emilia Käsper] + *) Tighten client-side session ticket handling during renegotiation: ensure that the client only accepts a session ticket if the server sends the extension anew in the ServerHello. Previously, a TLS client would @@ -638,6 +643,11 @@ Changes between 1.0.1j and 1.0.1k [xx XXX xxxx] + *) Tighten handling of the ChangeCipherSpec (CCS) message: reject + early CCS messages during renegotiation. (Note that because + renegotiation is encrypted, this early CCS was not exploitable.) + [Emilia Käsper] + *) Tighten client-side session ticket handling during renegotiation: ensure that the client only accepts a session ticket if the server sends the extension anew in the ServerHello. Previously, a TLS client would diff --git a/ssl/d1_clnt.c b/ssl/d1_clnt.c index 171d144586..ea36ea448a 100644 --- a/ssl/d1_clnt.c +++ b/ssl/d1_clnt.c @@ -267,6 +267,9 @@ int dtls1_connect(SSL *s) memset(s->s3->client_random,0,sizeof(s->s3->client_random)); s->d1->send_cookie = 0; s->hit = 0; + s->d1->change_cipher_spec_ok = 0; + /* Should have been reset by ssl3_get_finished, too. */ + s->s3->change_cipher_spec = 0; break; #ifndef OPENSSL_NO_SCTP @@ -510,7 +513,6 @@ int dtls1_connect(SSL *s) else #endif s->state=SSL3_ST_CW_CHANGE_A; - s->s3->change_cipher_spec=0; } s->init_num=0; @@ -531,7 +533,6 @@ int dtls1_connect(SSL *s) #endif s->state=SSL3_ST_CW_CHANGE_A; s->init_num=0; - s->s3->change_cipher_spec=0; break; case SSL3_ST_CW_CHANGE_A: diff --git a/ssl/d1_srvr.c b/ssl/d1_srvr.c index 1d2201de45..aef38bb754 100644 --- a/ssl/d1_srvr.c +++ b/ssl/d1_srvr.c @@ -264,6 +264,9 @@ int dtls1_accept(SSL *s) } s->init_num=0; + s->d1->change_cipher_spec_ok = 0; + /* Should have been reset by ssl3_get_finished, too. */ + s->s3->change_cipher_spec = 0; if (s->state != SSL_ST_RENEGOTIATE) { @@ -694,8 +697,14 @@ int dtls1_accept(SSL *s) case SSL3_ST_SR_CERT_VRFY_A: case SSL3_ST_SR_CERT_VRFY_B: - - s->d1->change_cipher_spec_ok = 1; + /* + * This *should* be the first time we enable CCS, but be + * extra careful about surrounding code changes. We need + * to set this here because we don't know if we're + * expecting a CertificateVerify or not. + */ + if (!s->s3->change_cipher_spec) + s->d1->change_cipher_spec_ok = 1; /* we should decide if we expected this one */ ret=ssl3_get_cert_verify(s); if (ret <= 0) goto end; @@ -711,7 +720,18 @@ int dtls1_accept(SSL *s) case SSL3_ST_SR_FINISHED_A: case SSL3_ST_SR_FINISHED_B: - s->d1->change_cipher_spec_ok = 1; + /* + * Enable CCS for resumed handshakes. + * In a full handshake, we end up here through + * SSL3_ST_SR_CERT_VRFY_B, so change_cipher_spec_ok was + * already set. Receiving a CCS clears the flag, so make + * sure not to re-enable it to ban duplicates. + * s->s3->change_cipher_spec is set when a CCS is + * processed in d1_pkt.c, and remains set until + * the client's Finished message is read. + */ + if (!s->s3->change_cipher_spec) + s->d1->change_cipher_spec_ok = 1; ret=ssl3_get_finished(s,SSL3_ST_SR_FINISHED_A, SSL3_ST_SR_FINISHED_B); if (ret <= 0) goto end; diff --git a/ssl/dtls1.h b/ssl/dtls1.h index 5cb79f1dac..af86f60fb5 100644 --- a/ssl/dtls1.h +++ b/ssl/dtls1.h @@ -256,6 +256,10 @@ typedef struct dtls1_state_st unsigned int handshake_fragment_len; unsigned int retransmitting; + /* + * Set when the handshake is ready to process peer's ChangeCipherSpec message. + * Cleared after the message has been processed. + */ unsigned int change_cipher_spec_ok; #ifndef OPENSSL_NO_SCTP diff --git a/ssl/s3_clnt.c b/ssl/s3_clnt.c index 64439c164a..ee0493f576 100644 --- a/ssl/s3_clnt.c +++ b/ssl/s3_clnt.c @@ -280,6 +280,9 @@ int ssl3_connect(SSL *s) s->state=SSL3_ST_CW_CLNT_HELLO_A; s->ctx->stats.sess_connect++; s->init_num=0; + s->s3->flags &= ~SSL3_FLAGS_CCS_OK; + /* Should have been reset by ssl3_get_finished, too. */ + s->s3->change_cipher_spec = 0; break; case SSL3_ST_CW_CLNT_HELLO_A: @@ -428,12 +431,10 @@ int ssl3_connect(SSL *s) else { s->state=SSL3_ST_CW_CHANGE_A; - s->s3->change_cipher_spec=0; } if (s->s3->flags & TLS1_FLAGS_SKIP_CERT_VERIFY) { s->state=SSL3_ST_CW_CHANGE_A; - s->s3->change_cipher_spec=0; } s->init_num=0; @@ -445,7 +446,6 @@ int ssl3_connect(SSL *s) if (ret <= 0) goto end; s->state=SSL3_ST_CW_CHANGE_A; s->init_num=0; - s->s3->change_cipher_spec=0; break; case SSL3_ST_CW_CHANGE_A: @@ -505,7 +505,6 @@ int ssl3_connect(SSL *s) s->method->ssl3_enc->client_finished_label, s->method->ssl3_enc->client_finished_label_len); if (ret <= 0) goto end; - s->s3->flags |= SSL3_FLAGS_CCS_OK; s->state=SSL3_ST_CW_FLUSH; /* clear flags */ @@ -554,7 +553,6 @@ int ssl3_connect(SSL *s) case SSL3_ST_CR_FINISHED_A: case SSL3_ST_CR_FINISHED_B: - s->s3->flags |= SSL3_FLAGS_CCS_OK; ret=ssl3_get_finished(s,SSL3_ST_CR_FINISHED_A, SSL3_ST_CR_FINISHED_B); @@ -992,7 +990,6 @@ int ssl3_get_server_hello(SSL *s) s->session->cipher = pref_cipher ? pref_cipher : ssl_get_cipher_by_char(s, p+j); s->hit = 1; - s->s3->flags |= SSL3_FLAGS_CCS_OK; } } #endif /* OPENSSL_NO_TLSEXT */ @@ -1008,7 +1005,6 @@ int ssl3_get_server_hello(SSL *s) SSLerr(SSL_F_SSL3_GET_SERVER_HELLO,SSL_R_ATTEMPT_TO_REUSE_SESSION_IN_DIFFERENT_CONTEXT); goto f_err; } - s->s3->flags |= SSL3_FLAGS_CCS_OK; s->hit=1; } /* a miss or crap from the other end */ diff --git a/ssl/s3_srvr.c b/ssl/s3_srvr.c index 876a245508..f79957f1d7 100644 --- a/ssl/s3_srvr.c +++ b/ssl/s3_srvr.c @@ -309,6 +309,9 @@ int ssl3_accept(SSL *s) s->init_num=0; s->s3->flags &= ~SSL3_FLAGS_SGC_RESTART_DONE; s->s3->flags &= ~TLS1_FLAGS_SKIP_CERT_VERIFY; + s->s3->flags &= ~SSL3_FLAGS_CCS_OK; + /* Should have been reset by ssl3_get_finished, too. */ + s->s3->change_cipher_spec = 0; if (s->state != SSL_ST_RENEGOTIATE) { @@ -683,8 +686,14 @@ int ssl3_accept(SSL *s) case SSL3_ST_SR_CERT_VRFY_A: case SSL3_ST_SR_CERT_VRFY_B: - - s->s3->flags |= SSL3_FLAGS_CCS_OK; + /* + * This *should* be the first time we enable CCS, but be + * extra careful about surrounding code changes. We need + * to set this here because we don't know if we're + * expecting a CertificateVerify or not. + */ + if (!s->s3->change_cipher_spec) + s->s3->flags |= SSL3_FLAGS_CCS_OK; /* we should decide if we expected this one */ ret=ssl3_get_cert_verify(s); if (ret <= 0) goto end; @@ -703,6 +712,19 @@ int ssl3_accept(SSL *s) #if !defined(OPENSSL_NO_TLSEXT) && !defined(OPENSSL_NO_NEXTPROTONEG) case SSL3_ST_SR_NEXT_PROTO_A: case SSL3_ST_SR_NEXT_PROTO_B: + /* + * Enable CCS for resumed handshakes with NPN. + * In a full handshake with NPN, we end up here through + * SSL3_ST_SR_CERT_VRFY_B, where SSL3_FLAGS_CCS_OK was + * already set. Receiving a CCS clears the flag, so make + * sure not to re-enable it to ban duplicates. + * s->s3->change_cipher_spec is set when a CCS is + * processed in s3_pkt.c, and remains set until + * the client's Finished message is read. + */ + if (!s->s3->change_cipher_spec) + s->s3->flags |= SSL3_FLAGS_CCS_OK; + ret=ssl3_get_next_proto(s); if (ret <= 0) goto end; s->init_num = 0; @@ -712,7 +734,18 @@ int ssl3_accept(SSL *s) case SSL3_ST_SR_FINISHED_A: case SSL3_ST_SR_FINISHED_B: - s->s3->flags |= SSL3_FLAGS_CCS_OK; + /* + * Enable CCS for resumed handshakes without NPN. + * In a full handshake, we end up here through + * SSL3_ST_SR_CERT_VRFY_B, where SSL3_FLAGS_CCS_OK was + * already set. Receiving a CCS clears the flag, so make + * sure not to re-enable it to ban duplicates. + * s->s3->change_cipher_spec is set when a CCS is + * processed in s3_pkt.c, and remains set until + * the client's Finished message is read. + */ + if (!s->s3->change_cipher_spec) + s->s3->flags |= SSL3_FLAGS_CCS_OK; ret=ssl3_get_finished(s,SSL3_ST_SR_FINISHED_A, SSL3_ST_SR_FINISHED_B); if (ret <= 0) goto end; @@ -784,7 +817,6 @@ int ssl3_accept(SSL *s) #else if (s->s3->next_proto_neg_seen) { - s->s3->flags |= SSL3_FLAGS_CCS_OK; s->s3->tmp.next_state=SSL3_ST_SR_NEXT_PROTO_A; } else diff --git a/ssl/ssl3.h b/ssl/ssl3.h index 276a7761b2..efff233fbd 100644 --- a/ssl/ssl3.h +++ b/ssl/ssl3.h @@ -433,8 +433,12 @@ typedef struct ssl3_buffer_st #define TLS1_FLAGS_TLS_PADDING_BUG 0x0008 #define TLS1_FLAGS_SKIP_CERT_VERIFY 0x0010 #define TLS1_FLAGS_KEEP_HANDSHAKE 0x0020 +/* + * Set when the handshake is ready to process peer's ChangeCipherSpec message. + * Cleared after the message has been processed. + */ #define SSL3_FLAGS_CCS_OK 0x0080 - + /* SSL3_FLAGS_SGC_RESTART_DONE is set when we * restart a handshake because of MS SGC and so prevents us * from restarting the handshake in a loop. It's reset on a @@ -498,8 +502,11 @@ typedef struct ssl3_state_st * and freed and MD_CTX-es for all required digests are stored in * this array */ EVP_MD_CTX **handshake_dgst; - /* this is set whenerver we see a change_cipher_spec message - * come in when we are not looking for one */ + /* + * Set whenever an expected ChangeCipherSpec message is processed. + * Unset when the peer's Finished message is received. + * Unexpected ChangeCipherSpec messages trigger a fatal alert. + */ int change_cipher_spec; int warn_alert; diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c index 86203f1d2a..8b2b16bc87 100644 --- a/ssl/t1_lib.c +++ b/ssl/t1_lib.c @@ -2504,7 +2504,7 @@ static int ssl_scan_serverhello_tlsext(SSL *s, unsigned char **p, unsigned char #ifndef OPENSSL_NO_NEXTPROTONEG s->s3->next_proto_neg_seen = 0; #endif - s->tlsext_ticket_expected = 0; + s->tlsext_ticket_expected = 0; if (s->s3->alpn_selected) { -- 2.25.1