From c7af59729a71f11a7c7892faabb0a74e388d1251 Mon Sep 17 00:00:00 2001 From: bwzhang Date: Mon, 29 Apr 2024 10:49:10 +0800 Subject: [PATCH] fix CVE-2023-48795 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit ssh: implement strict KEX protocol changes Implement the "strict KEX" protocol changes, as described in section 1.9 of the OpenSSH PROTOCOL file (as of OpenSSH version 9.6/9.6p1). Namely this makes the following changes: * Both the server and the client add an additional algorithm to the initial KEXINIT message, indicating support for the strict KEX mode. * When one side of the connection sees the strict KEX extension algorithm, the strict KEX mode is enabled for messages originating from the other side of the connection. If the sequence number for the side which requested the extension is not 1 (indicating that it has already received non-KEXINIT packets), the connection is terminated. * When strict kex mode is enabled, unexpected messages during the handshake are considered fatal. Additionally when a key change occurs (on the receipt of the NEWKEYS message) the message sequence numbers are reset. Thanks to Fabian Bäumer, Marcus Brinkmann, and Jörg Schwenk from Ruhr University Bochum for reporting this issue. Fixes CVE-2023-48795 Fixes golang/go#64784 Change-Id: I96b53afd2bd2fb94d2b6f2a46a5dacf325357604 Reviewed-on: https://go-review.googlesource.com/c/crypto/+/550715 Reviewed-by: Nicola Murino Reviewed-by: Tatiana Bradley TryBot-Result: Gopher Robot Run-TryBot: Roland Shoemaker Reviewed-by: Damien Neil LUCI-TryBot-Result: Go LUCI --- .../golang.org/x/crypto/ssh/handshake.go | 55 +++++++++++++++++-- .../golang.org/x/crypto/ssh/transport.go | 32 +++++++++-- 2 files changed, 78 insertions(+), 9 deletions(-) diff --git a/gvisor-tap-vsock-0.7.1/vendor/golang.org/x/crypto/ssh/handshake.go b/gvisor-tap-vsock-0.7.1/vendor/golang.org/x/crypto/ssh/handshake.go index 07a1843..97659b1 100644 --- a/gvisor-tap-vsock-0.7.1/vendor/golang.org/x/crypto/ssh/handshake.go +++ b/gvisor-tap-vsock-0.7.1/vendor/golang.org/x/crypto/ssh/handshake.go @@ -34,6 +34,16 @@ type keyingTransport interface { // direction will be effected if a msgNewKeys message is sent // or received. prepareKeyChange(*algorithms, *kexResult) error + + // setStrictMode sets the strict KEX mode, notably triggering + // sequence number resets on sending or receiving msgNewKeys. + // If the sequence number is already > 1 when setStrictMode + // is called, an error is returned. + setStrictMode() error + + // setInitialKEXDone indicates to the transport that the initial key exchange + // was completed + setInitialKEXDone() } // handshakeTransport implements rekeying on top of a keyingTransport @@ -95,6 +105,10 @@ type handshakeTransport struct { // The session ID or nil if first kex did not complete yet. sessionID []byte + + // strictMode indicates if the other side of the handshake indicated + // that we should be following the strict KEX protocol restrictions. + strictMode bool } type pendingKex struct { @@ -203,7 +217,10 @@ func (t *handshakeTransport) readLoop() { close(t.incoming) break } - if p[0] == msgIgnore || p[0] == msgDebug { + // If this is the first kex, and strict KEX mode is enabled, + // we don't ignore any messages, as they may be used to manipulate + // the packet sequence numbers. + if !(t.sessionID == nil && t.strictMode) && (p[0] == msgIgnore || p[0] == msgDebug) { continue } t.incoming <- p @@ -435,6 +452,11 @@ func (t *handshakeTransport) readOnePacket(first bool) ([]byte, error) { return successPacket, nil } +const ( + kexStrictClient = "kex-strict-c-v00@openssh.com" + kexStrictServer = "kex-strict-s-v00@openssh.com" +) + // sendKexInit sends a key change message. func (t *handshakeTransport) sendKexInit() error { t.mu.Lock() @@ -448,7 +470,6 @@ func (t *handshakeTransport) sendKexInit() error { } msg := &kexInitMsg{ - KexAlgos: t.config.KeyExchanges, CiphersClientServer: t.config.Ciphers, CiphersServerClient: t.config.Ciphers, MACsClientServer: t.config.MACs, @@ -458,6 +479,13 @@ func (t *handshakeTransport) sendKexInit() error { } io.ReadFull(rand.Reader, msg.Cookie[:]) + // We mutate the KexAlgos slice, in order to add the kex-strict extension algorithm, + // and possibly to add the ext-info extension algorithm. Since the slice may be the + // user owned KeyExchanges, we create our own slice in order to avoid using user + // owned memory by mistake. + msg.KexAlgos = make([]string, 0, len(t.config.KeyExchanges)+2) // room for kex-strict and ext-info + msg.KexAlgos = append(msg.KexAlgos, t.config.KeyExchanges...) + isServer := len(t.hostKeys) > 0 if isServer { for _, k := range t.hostKeys { @@ -477,16 +505,22 @@ func (t *handshakeTransport) sendKexInit() error { msg.ServerHostKeyAlgos = append(msg.ServerHostKeyAlgos, keyFormat) } } + + if t.sessionID == nil { + msg.KexAlgos = append(msg.KexAlgos, kexStrictServer) + } } else { msg.ServerHostKeyAlgos = t.hostKeyAlgorithms // As a client we opt in to receiving SSH_MSG_EXT_INFO so we know what // algorithms the server supports for public key authentication. See RFC // 8308, Section 2.1. + // + // We also send the strict KEX mode extension algorithm, in order to opt + // into the strict KEX mode. if firstKeyExchange := t.sessionID == nil; firstKeyExchange { - msg.KexAlgos = make([]string, 0, len(t.config.KeyExchanges)+1) - msg.KexAlgos = append(msg.KexAlgos, t.config.KeyExchanges...) msg.KexAlgos = append(msg.KexAlgos, "ext-info-c") + msg.KexAlgos = append(msg.KexAlgos, kexStrictClient) } } @@ -593,6 +627,13 @@ func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error { return err } + if t.sessionID == nil && ((isClient && contains(serverInit.KexAlgos, kexStrictServer)) || (!isClient && contains(clientInit.KexAlgos, kexStrictClient))) { + t.strictMode = true + if err := t.conn.setStrictMode(); err != nil { + return err + } + } + // We don't send FirstKexFollows, but we handle receiving it. // // RFC 4253 section 7 defines the kex and the agreement method for @@ -663,6 +704,12 @@ func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error { return unexpectedMessageError(msgNewKeys, packet[0]) } + if firstKeyExchange { + // Indicates to the transport that the first key exchange is completed + // after receiving SSH_MSG_NEWKEYS. + t.conn.setInitialKEXDone() + } + return nil } diff --git a/gvisor-tap-vsock-0.7.1/vendor/golang.org/x/crypto/ssh/transport.go b/gvisor-tap-vsock-0.7.1/vendor/golang.org/x/crypto/ssh/transport.go index da01580..0424d2d 100644 --- a/gvisor-tap-vsock-0.7.1/vendor/golang.org/x/crypto/ssh/transport.go +++ b/gvisor-tap-vsock-0.7.1/vendor/golang.org/x/crypto/ssh/transport.go @@ -49,6 +49,9 @@ type transport struct { rand io.Reader isClient bool io.Closer + + strictMode bool + initialKEXDone bool } // packetCipher represents a combination of SSH encryption/MAC @@ -74,6 +77,18 @@ type connectionState struct { pendingKeyChange chan packetCipher } +func (t *transport) setStrictMode() error { + if t.reader.seqNum != 1 { + return errors.New("ssh: sequence number != 1 when strict KEX mode requested") + } + t.strictMode = true + return nil +} + +func (t *transport) setInitialKEXDone() { + t.initialKEXDone = true +} + // prepareKeyChange sets up key material for a keychange. The key changes in // both directions are triggered by reading and writing a msgNewKey packet // respectively. @@ -112,11 +127,12 @@ func (t *transport) printPacket(p []byte, write bool) { // Read and decrypt next packet. func (t *transport) readPacket() (p []byte, err error) { for { - p, err = t.reader.readPacket(t.bufReader) + p, err = t.reader.readPacket(t.bufReader, t.strictMode) if err != nil { break } - if len(p) == 0 || (p[0] != msgIgnore && p[0] != msgDebug) { + // in strict mode we pass through DEBUG and IGNORE packets only during the initial KEX + if len(p) == 0 || (t.strictMode && !t.initialKEXDone) || (p[0] != msgIgnore && p[0] != msgDebug) { break } } @@ -127,7 +143,7 @@ func (t *transport) readPacket() (p []byte, err error) { return p, err } -func (s *connectionState) readPacket(r *bufio.Reader) ([]byte, error) { +func (s *connectionState) readPacket(r *bufio.Reader, strictMode bool) ([]byte, error) { packet, err := s.packetCipher.readCipherPacket(s.seqNum, r) s.seqNum++ if err == nil && len(packet) == 0 { @@ -140,6 +156,9 @@ func (s *connectionState) readPacket(r *bufio.Reader) ([]byte, error) { select { case cipher := <-s.pendingKeyChange: s.packetCipher = cipher + if strictMode { + s.seqNum = 0 + } default: return nil, errors.New("ssh: got bogus newkeys message") } @@ -170,10 +189,10 @@ func (t *transport) writePacket(packet []byte) error { if debugTransport { t.printPacket(packet, true) } - return t.writer.writePacket(t.bufWriter, t.rand, packet) + return t.writer.writePacket(t.bufWriter, t.rand, packet, t.strictMode) } -func (s *connectionState) writePacket(w *bufio.Writer, rand io.Reader, packet []byte) error { +func (s *connectionState) writePacket(w *bufio.Writer, rand io.Reader, packet []byte, strictMode bool) error { changeKeys := len(packet) > 0 && packet[0] == msgNewKeys err := s.packetCipher.writeCipherPacket(s.seqNum, w, rand, packet) @@ -188,6 +207,9 @@ func (s *connectionState) writePacket(w *bufio.Writer, rand io.Reader, packet [] select { case cipher := <-s.pendingKeyChange: s.packetCipher = cipher + if strictMode { + s.seqNum = 0 + } default: panic("ssh: no key material for msgNewKeys") } -- 2.20.1