Merge pull request #1356 from p12tic/2.3-security-fixes

Backports of security fixes to 2.3.x

doc/newsfragments/close-failed-handshake-connections.bugfix

@@ -0,0 +1,6 @@
+SECURITY ISSUE
+
+Barrier will now correctly close connections when the app-level handshake fails (fixes CVE-2021-42075).
+
+Previously repeated failing connections would leak file descriptors leading to Barrier being unable
+to receive new connections from clients.

doc/newsfragments/enforce-maximum-message-length.bugfix

@@ -0,0 +1,6 @@
+SECURITY ISSUE
+
+Barrier will now enforce a maximum length of input messages (fixes CVE-2021-42076).
+
+Previously it was possible for a malicious client or server to send excessive length messages
+leading to denial of service by resource exhaustion.

doc/newsfragments/fix-crash-on-ssl-hello.bugfix

@@ -0,0 +1,4 @@
+SECURITY ISSUE
+
+Fixed a bug which caused Barrier to crash when disconnecting a TCP session just after sending Hello message.
+This bug allowed an unauthenticated attacker to crash Barrier with only network access.

doc/newsfragments/ssl-corrupted-data.bugfix

@@ -0,0 +1,2 @@
+Fixed a bug in SSL implementation that caused invalid data occasionally being sent to clients
+under heavy load.

src/lib/barrier/PacketStreamFilter.cpp

@@ -17,6 +17,7 @@
  */
 
 #include "barrier/PacketStreamFilter.h"
+#include "barrier/protocol_types.h"
 #include "base/IEventQueue.h"
 #include "mt/Lock.h"
 #include "base/TMethodEventJob.h"
@@ -133,8 +134,7 @@ PacketStreamFilter::isReadyNoLock() const
     return (m_size != 0 && m_buffer.getSize() >= m_size);
 }
 
-void
+bool PacketStreamFilter::readPacketSize()
-PacketStreamFilter::readPacketSize()
 {
     // note -- m_mutex must be locked on entry
 
@@ -146,7 +146,13 @@ PacketStreamFilter::readPacketSize()
                  ((UInt32)buffer[1] << 16) |
                  ((UInt32)buffer[2] <<  8) |
                   (UInt32)buffer[3];
+
+        if (m_size > PROTOCOL_MAX_MESSAGE_LENGTH) {
+            m_events->addEvent(Event(m_events->forIStream().inputFormatError(), getEventTarget()));
+            return false;
         }
+    }
+    return true;
 }
 
 bool
@@ -160,12 +166,16 @@ PacketStreamFilter::readMore()
     UInt32 n = getStream()->read(buffer, sizeof(buffer));
     while (n > 0) {
         m_buffer.write(buffer, n);
-        n = getStream()->read(buffer, sizeof(buffer));
+
+        // if we don't yet have the next packet size then get it, if possible.
+        // Note that we can't wait for whole pending data to arrive because it may be huge in
+        // case of malicious or erroneous peer.
+        if (!readPacketSize()) {
+            break;
         }
 
-    // if we don't yet have the next packet size then get it,
+        n = getStream()->read(buffer, sizeof(buffer));
-    // if possible.
+    }
-    readPacketSize();
 
     // note if we now have a whole packet
     bool isReady = isReadyNoLock();

src/lib/barrier/PacketStreamFilter.h

@@ -47,7 +47,9 @@ protected:
 
 private:
     bool                isReadyNoLock() const;
-    void                readPacketSize();
+
+    // returns false on erroneous packet size
+    bool readPacketSize();
     bool                readMore();
 
 private:

src/lib/barrier/ProtocolUtil.cpp

@@ -19,6 +19,8 @@
 #include "barrier/ProtocolUtil.h"
 #include "io/IStream.h"
 #include "base/Log.h"
+#include "barrier/protocol_types.h"
+#include "barrier/XBarrier.h"
 #include "common/stdvector.h"
 #include "base/String.h"
 
@@ -159,6 +161,10 @@ ProtocolUtil::vreadf(barrier::IStream* stream, const char* fmt, va_list args)
                            (static_cast<UInt32>(buffer[2]) <<  8) |
                             static_cast<UInt32>(buffer[3]);
 
+                if (n > PROTOCOL_MAX_LIST_LENGTH) {
+                    throw XBadClient("Too long message received");
+                }
+
                 // convert it
                 void* v = va_arg(args, void*);
                 switch (len) {
@@ -211,6 +217,10 @@ ProtocolUtil::vreadf(barrier::IStream* stream, const char* fmt, va_list args)
                              (static_cast<UInt32>(buffer[2]) <<  8) |
                               static_cast<UInt32>(buffer[3]);
 
+                if (len > PROTOCOL_MAX_STRING_LENGTH) {
+                    throw XBadClient("Too long message received");
+                }
+
                 // use a fixed size buffer if its big enough
                 const bool useFixed = (len <= sizeof(buffer));
 

src/lib/barrier/protocol_types.h

@@ -20,6 +20,8 @@
 
 #include "base/EventTypes.h"
 
+#include <cstdint>
+
 // protocol version number
 // 1.0:  initial protocol
 // 1.1:  adds KeyCode to key press, release, and repeat
@@ -51,6 +53,12 @@ static const double        kKeepAlivesUntilDeath = 3.0;
 static const double        kHeartRate = -1.0;
 static const double        kHeartBeatsUntilDeath = 3.0;
 
+// Messages of very large size indicate a likely protocol error. We don't parse such messages and
+// drop connection instead. Note that e.g. the clipboard messages are already limited to 32kB.
+static constexpr std::uint32_t PROTOCOL_MAX_MESSAGE_LENGTH = 4 * 1024 * 1024;
+static constexpr std::uint32_t PROTOCOL_MAX_LIST_LENGTH = 1024 * 1024;
+static constexpr std::uint32_t PROTOCOL_MAX_STRING_LENGTH = 1024 * 1024;
+
 // direction constants
 enum EDirection {
     kNoDirection,

src/lib/base/EventTypes.cpp

@@ -56,6 +56,7 @@ REGISTER_EVENT(IStream, outputFlushed)
 REGISTER_EVENT(IStream, outputError)
 REGISTER_EVENT(IStream, inputShutdown)
 REGISTER_EVENT(IStream, outputShutdown)
+REGISTER_EVENT(IStream, inputFormatError)
 
 //
 // IpcClient

src/lib/base/EventTypes.h

@@ -133,6 +133,11 @@ public:
     */
     Event::Type        outputShutdown();
 
+    /** Get input format error event type
+
+        This is sent when a stream receives an irrecoverable input format error.
+    */
+    Event::Type inputFormatError();
     //@}
         
 private:
@@ -141,6 +146,7 @@ private:
     Event::Type        m_outputError;
     Event::Type        m_inputShutdown;
     Event::Type        m_outputShutdown;
+    Event::Type m_inputFormatError;
 };
 
 class IpcClientEvents : public EventTypes {

src/lib/client/ServerProxy.cpp

@@ -26,6 +26,7 @@
 #include "barrier/ProtocolUtil.h"
 #include "barrier/option_types.h"
 #include "barrier/protocol_types.h"
+#include "barrier/XBarrier.h"
 #include "io/IStream.h"
 #include "base/Log.h"
 #include "base/IEventQueue.h"
@@ -124,6 +125,7 @@ ServerProxy::handleData(const Event&, void*)
 
         // parse message
         LOG((CLOG_DEBUG2 "msg from server: %c%c%c%c", code[0], code[1], code[2], code[3]));
+        try {
             switch ((this->*m_parser)(code)) {
             case kOkay:
                 break;
@@ -136,6 +138,15 @@ ServerProxy::handleData(const Event&, void*)
             case kDisconnect:
                 return;
             }
+        } catch (const XBadClient& e) {
+            // TODO: disconnect handling is currently dispersed across both parseMessage() and
+            // handleData() functions, we should collect that to a single place
+
+            LOG((CLOG_ERR "protocol error from server: %s", e.what()));
+            ProtocolUtil::writef(m_stream, kMsgEBad);
+            m_client->disconnect("invalid message from server");
+            return;
+        }
 
         // next message
         n = m_stream->read(code, 4);

src/lib/net/SecureSocket.cpp

@@ -40,6 +40,7 @@
 
 #define MAX_ERROR_SIZE 65535
 
+static const std::size_t MAX_INPUT_BUFFER_SIZE = 1024 * 1024;
 static const float s_retryDelay = 0.01f;
 
 enum {
@@ -103,6 +104,8 @@ SecureSocket::close()
 
 void SecureSocket::freeSSLResources()
 {
+    std::lock_guard<std::mutex> ssl_lock{ssl_mutex_};
+
     if (m_ssl->m_ssl != NULL) {
         SSL_shutdown(m_ssl->m_ssl);
         SSL_free(m_ssl->m_ssl);
@@ -156,7 +159,7 @@ SecureSocket::secureAccept()
 TCPSocket::EJobResult
 SecureSocket::doRead()
 {
-    static UInt8 buffer[4096];
+    UInt8 buffer[4096];
     memset(buffer, 0, sizeof(buffer));
     int bytesRead = 0;
     int status = 0;
@@ -181,6 +184,10 @@ SecureSocket::doRead()
         do {
             m_inputBuffer.write(buffer, bytesRead);
 
+            if (m_inputBuffer.getSize() > MAX_INPUT_BUFFER_SIZE) {
+                break;
+            }
+
             status = secureRead(buffer, sizeof(buffer), bytesRead);
             if (status < 0) {
                 return kBreak;
@@ -211,11 +218,6 @@ SecureSocket::doRead()
 TCPSocket::EJobResult
 SecureSocket::doWrite()
 {
-    static bool s_retry = false;
-    static int s_retrySize = 0;
-    static std::unique_ptr<char[]> s_staticBuffer;
-    static std::size_t s_staticBufferSize = 0;
-
     // write data
     int bufferSize = 0;
     int bytesWrote = 0;
@@ -224,16 +226,16 @@ SecureSocket::doWrite()
     if (!isSecureReady())
         return kRetry;
 
-    if (s_retry) {
+    if (do_write_retry_) {
-        bufferSize = s_retrySize;
+        bufferSize = do_write_retry_size_;
     } else {
         bufferSize = m_outputBuffer.getSize();
-        if (bufferSize > s_staticBufferSize) {
+        if (bufferSize > do_write_retry_buffer_size_) {
-            s_staticBuffer.reset(new char[bufferSize]);
+            do_write_retry_buffer_.reset(new char[bufferSize]);
-            s_staticBufferSize = bufferSize;
+            do_write_retry_buffer_size_ = bufferSize;
         }
         if (bufferSize > 0) {
-            memcpy(s_staticBuffer.get(), m_outputBuffer.peek(bufferSize), bufferSize);
+            std::memcpy(do_write_retry_buffer_.get(), m_outputBuffer.peek(bufferSize), bufferSize);
         }
     }
     
@@ -241,14 +243,14 @@ SecureSocket::doWrite()
         return kRetry;
     }
 
-    status = secureWrite(s_staticBuffer.get(), bufferSize, bytesWrote);
+    status = secureWrite(do_write_retry_buffer_.get(), bufferSize, bytesWrote);
     if (status > 0) {
-        s_retry = false;
+        do_write_retry_ = false;
     } else if (status < 0) {
         return kBreak;
     } else if (status == 0) {
-        s_retry = true;
+        do_write_retry_ = true;
-        s_retrySize = bufferSize;
+        do_write_retry_size_ = bufferSize;
         return kNew;
     }
     
@@ -263,16 +265,16 @@ SecureSocket::doWrite()
 int
 SecureSocket::secureRead(void* buffer, int size, int& read)
 {
+    std::lock_guard<std::mutex> ssl_lock{ssl_mutex_};
+
     if (m_ssl->m_ssl != NULL) {
         LOG((CLOG_DEBUG2 "reading secure socket"));
         read = SSL_read(m_ssl->m_ssl, buffer, size);
 
-        static int retry;
-
         // Check result will cleanup the connection in the case of a fatal
-        checkResult(read, retry);
+        checkResult(read, secure_read_retry_);
 
-        if (retry) {
+        if (secure_read_retry_) {
             return 0;
         }
 
@@ -289,17 +291,17 @@ SecureSocket::secureRead(void* buffer, int size, int& read)
 int
 SecureSocket::secureWrite(const void* buffer, int size, int& wrote)
 {
+    std::lock_guard<std::mutex> ssl_lock{ssl_mutex_};
+
     if (m_ssl->m_ssl != NULL) {
         LOG((CLOG_DEBUG2 "writing secure socket:%p", this));
 
         wrote = SSL_write(m_ssl->m_ssl, buffer, size);
 
-        static int retry;
-
         // Check result will cleanup the connection in the case of a fatal
-        checkResult(wrote, retry);
+        checkResult(wrote, secure_write_retry_);
 
-        if (retry) {
+        if (secure_write_retry_) {
             return 0;
         }
 
@@ -322,6 +324,8 @@ SecureSocket::isSecureReady()
 void
 SecureSocket::initSsl(bool server)
 {
+    std::lock_guard<std::mutex> ssl_lock{ssl_mutex_};
+
     m_ssl = new Ssl();
     m_ssl->m_context = NULL;
     m_ssl->m_ssl = NULL;
@@ -331,6 +335,8 @@ SecureSocket::initSsl(bool server)
 
 bool SecureSocket::loadCertificates(std::string& filename)
 {
+    std::lock_guard<std::mutex> ssl_lock{ssl_mutex_};
+
     if (filename.empty()) {
         showError("ssl certificate is not specified");
         return false;
@@ -373,6 +379,8 @@ bool SecureSocket::loadCertificates(std::string& filename)
 void
 SecureSocket::initContext(bool server)
 {
+    // ssl_mutex_ is assumed to be acquired
+
     SSL_library_init();
 
     const SSL_METHOD* method;
@@ -410,6 +418,8 @@ SecureSocket::initContext(bool server)
 void
 SecureSocket::createSSL()
 {
+    // ssl_mutex_ is assumed to be acquired
+
     // I assume just one instance is needed
     // get new SSL state with context
     if (m_ssl->m_ssl == NULL) {
@@ -421,6 +431,8 @@ SecureSocket::createSSL()
 int
 SecureSocket::secureAccept(int socket)
 {
+    std::lock_guard<std::mutex> ssl_lock{ssl_mutex_};
+
     createSSL();
 
     // set connection socket to SSL state
@@ -429,9 +441,7 @@ SecureSocket::secureAccept(int socket)
     LOG((CLOG_DEBUG2 "accepting secure socket"));
     int r = SSL_accept(m_ssl->m_ssl);
 
-    static int retry;
+    checkResult(r, secure_accept_retry_);
-
-    checkResult(r, retry);
 
     if (isFatal()) {
         // tell user and sleep so the socket isn't hammered.
@@ -439,12 +449,12 @@ SecureSocket::secureAccept(int socket)
         LOG((CLOG_INFO "client connection may not be secure"));
         m_secureReady = false;
         ARCH->sleep(1);
-        retry = 0;
+        secure_accept_retry_ = 0;
         return -1; // Failed, error out
     }
 
     // If not fatal and no retry, state is good
-    if (retry == 0) {
+    if (secure_accept_retry_ == 0) {
         m_secureReady = true;
         LOG((CLOG_INFO "accepted secure socket"));
         if (CLOG->getFilter() >= kDEBUG1) {
@@ -455,7 +465,7 @@ SecureSocket::secureAccept(int socket)
     }
 
     // If not fatal and retry is set, not ready, and return retry
-    if (retry > 0) {
+    if (secure_accept_retry_ > 0) {
         LOG((CLOG_DEBUG2 "retry accepting secure socket"));
         m_secureReady = false;
         ARCH->sleep(s_retryDelay);
@@ -470,6 +480,8 @@ SecureSocket::secureAccept(int socket)
 int
 SecureSocket::secureConnect(int socket)
 {
+    std::lock_guard<std::mutex> ssl_lock{ssl_mutex_};
+
     createSSL();
 
     // attach the socket descriptor
@@ -478,25 +490,23 @@ SecureSocket::secureConnect(int socket)
     LOG((CLOG_DEBUG2 "connecting secure socket"));
     int r = SSL_connect(m_ssl->m_ssl);
 
-    static int retry;
+    checkResult(r, secure_connect_retry_);
-
-    checkResult(r, retry);
 
     if (isFatal()) {
         LOG((CLOG_ERR "failed to connect secure socket"));
-        retry = 0;
+        secure_connect_retry_ = 0;
         return -1;
     }
 
     // If we should retry, not ready and return 0
-    if (retry > 0) {
+    if (secure_connect_retry_ > 0) {
         LOG((CLOG_DEBUG2 "retry connect secure socket"));
         m_secureReady = false;
         ARCH->sleep(s_retryDelay);
         return 0;
     }
 
-    retry = 0;
+    secure_connect_retry_ = 0;
     // No error, set ready, process and return ok
     m_secureReady = true;
     if (verifyCertFingerprint()) {
@@ -522,6 +532,7 @@ SecureSocket::secureConnect(int socket)
 bool
 SecureSocket::showCertificate()
 {
+    // ssl_mutex_ is assumed to be acquired
     X509* cert;
     char* line;
  
@@ -544,6 +555,8 @@ SecureSocket::showCertificate()
 void
 SecureSocket::checkResult(int status, int& retry)
 {
+    // ssl_mutex_ is assumed to be acquired
+
     // ssl errors are a little quirky. the "want" errors are normal and
     // should result in a retry.
 
@@ -680,6 +693,8 @@ void SecureSocket::formatFingerprint(std::string& fingerprint, bool hex, bool se
 bool
 SecureSocket::verifyCertFingerprint()
 {
+    // ssl_mutex_ is assumed to be acquired
+
     // calculate received certificate fingerprint
     X509 *cert = cert = SSL_get_peer_certificate(m_ssl->m_ssl);
     EVP_MD* tempDigest;
@@ -822,6 +837,8 @@ showCipherStackDesc(STACK_OF(SSL_CIPHER) * stack) {
 void
 SecureSocket::showSecureCipherInfo()
 {
+    // ssl_mutex_ is assumed to be acquired
+
     STACK_OF(SSL_CIPHER) * sStack = SSL_get_ciphers(m_ssl->m_ssl);
 
     if (sStack == NULL) {
@@ -864,6 +881,8 @@ SecureSocket::showSecureLibInfo()
 void
 SecureSocket::showSecureConnectInfo()
 {
+    // ssl_mutex_ is assumed to be acquired
+
     const SSL_CIPHER* cipher = SSL_get_current_cipher(m_ssl->m_ssl);
 
     if (cipher != NULL) {

src/lib/net/SecureSocket.h

@@ -19,6 +19,7 @@
 
 #include "net/TCPSocket.h"
 #include "net/XSocket.h"
+#include <mutex>
 
 class IEventQueue;
 class SocketMultiplexer;
@@ -59,31 +60,48 @@ public:
 
 private:
     // SSL
-    void                initContext(bool server);
+    void initContext(bool server); // may only be called with ssl_mutex_ acquired
-    void                createSSL();
+    void createSSL(); // may only be called with ssl_mutex_ acquired.
     int                    secureAccept(int s);
     int                    secureConnect(int s);
-    bool                showCertificate();
+    bool showCertificate(); // may only be called with ssl_mutex_ acquired
-    void                checkResult(int n, int& retry);
+    void checkResult(int n, int& retry); // may only be called with m_ssl_mutex_ acquired.
     void                showError(const char* reason = NULL);
     std::string getError();
     void                disconnect();
     void formatFingerprint(std::string& fingerprint, bool hex = true, bool separator = true);
-    bool                verifyCertFingerprint();
+    bool verifyCertFingerprint(); // may only be called with ssl_mutex_ acquired
 
     MultiplexerJobStatus serviceConnect(ISocketMultiplexerJob*, bool, bool, bool);
     MultiplexerJobStatus serviceAccept(ISocketMultiplexerJob*, bool, bool, bool);
 
-    void                showSecureConnectInfo();
+    void showSecureConnectInfo(); // may only be called with ssl_mutex_ acquired
     void showSecureLibInfo();
-    void                showSecureCipherInfo();
+    void showSecureCipherInfo(); // may only be called with ssl_mutex_ acquired
 
     void                handleTCPConnected(const Event& event, void*);
 
     void freeSSLResources();
 
 private:
+    // all accesses to m_ssl must be protected by this mutex. The only function that is called
+    // from outside SocketMultiplexer thread is close(), so we mostly care about things accessed
+    // by it.
+    std::mutex ssl_mutex_;
+
     Ssl*                m_ssl;
     bool                m_secureReady;
     bool                m_fatal;
+
+    int secure_accept_retry_ = 0; // used only in secureAccept()
+    int secure_connect_retry_ = 0; // used only in secureConnect()
+    int secure_read_retry_ = 0; // used only in secureRead()
+    int secure_write_retry_ = 0; // used only in secureWrite()
+
+    // The following are used only from doWrite()
+    // FIXME: using std::vector would simplify logic significantly.
+    bool do_write_retry_ = false;
+    int do_write_retry_size_ = 0;
+    std::unique_ptr<char[]> do_write_retry_buffer_;
+    std::size_t do_write_retry_buffer_size_ = 0;
 };

src/lib/net/TCPSocket.cpp

@@ -33,9 +33,7 @@
 #include <cstdlib>
 #include <memory>
 
-//
+static const std::size_t MAX_INPUT_BUFFER_SIZE = 1024 * 1024;
-// TCPSocket
-//
 
 TCPSocket::TCPSocket(IEventQueue* events, SocketMultiplexer* socketMultiplexer, IArchNetwork::EAddressFamily family) :
     IDataSocket(events),
@@ -345,6 +343,10 @@ TCPSocket::doRead()
         do {
             m_inputBuffer.write(buffer, (UInt32)bytesRead);
 
+            if (m_inputBuffer.getSize() > MAX_INPUT_BUFFER_SIZE) {
+                break;
+            }
+
             bytesRead = ARCH->readSocket(m_socket, buffer, sizeof(buffer));
         } while (bytesRead > 0);
         

src/lib/server/ClientListener.cpp

@@ -184,7 +184,6 @@ ClientListener::handleUnknownClient(const Event&, void* vclient)
 
     // get the real client proxy and install it
     ClientProxy* client = unknownClient->orphanClientProxy();
-    bool handshakeOk = true;
     if (client != NULL) {
         // handshake was successful
         m_waitingClients.push_back(client);
@@ -196,20 +195,17 @@ ClientListener::handleUnknownClient(const Event&, void* vclient)
                             new TMethodEventJob<ClientListener>(this,
                                 &ClientListener::handleClientDisconnected,
                                 client));
+    } else {
+        auto* stream = unknownClient->getStream();
+        if (stream) {
+            stream->close();
         }
-    else {
-        handshakeOk = false;
     }
 
     // now finished with unknown client
     m_events->removeHandler(m_events->forClientProxyUnknown().success(), client);
     m_events->removeHandler(m_events->forClientProxyUnknown().failure(), client);
     m_newClients.erase(unknownClient);
-    PacketStreamFilter* streamFileter = dynamic_cast<PacketStreamFilter*>(unknownClient->getStream());
-    IDataSocket* socket = NULL;
-    if (streamFileter != NULL) {
-        socket = dynamic_cast<IDataSocket*>(streamFileter->getStream());
-    }
 
     delete unknownClient;
 }

src/lib/server/ClientProxy1_0.cpp

@@ -51,6 +51,10 @@ ClientProxy1_0::ClientProxy1_0(const std::string& name, barrier::IStream* stream
                             stream->getEventTarget(),
                             new TMethodEventJob<ClientProxy1_0>(this,
                                 &ClientProxy1_0::handleDisconnect, NULL));
+    m_events->adoptHandler(m_events->forIStream().inputFormatError(),
+                           stream->getEventTarget(),
+                           new TMethodEventJob<ClientProxy1_0>(this,
+                                &ClientProxy1_0::handleDisconnect, NULL));
     m_events->adoptHandler(m_events->forIStream().outputShutdown(),
                             stream->getEventTarget(),
                             new TMethodEventJob<ClientProxy1_0>(this,
@@ -90,6 +94,8 @@ ClientProxy1_0::removeHandlers()
                             getStream()->getEventTarget());
     m_events->removeHandler(m_events->forIStream().outputShutdown(),
                             getStream()->getEventTarget());
+    m_events->removeHandler(m_events->forIStream().inputFormatError(),
+                            getStream()->getEventTarget());
     m_events->removeHandler(Event::kTimer, this);
 
     // remove timer
@@ -148,12 +154,21 @@ ClientProxy1_0::handleData(const Event&, void*)
         }
 
         // parse message
+        try {
             LOG((CLOG_DEBUG2 "msg from \"%s\": %c%c%c%c", getName().c_str(), code[0], code[1], code[2], code[3]));
             if (!(this->*m_parser)(code)) {
                 LOG((CLOG_ERR "invalid message from client \"%s\": %c%c%c%c", getName().c_str(), code[0], code[1], code[2], code[3]));
                 disconnect();
                 return;
             }
+        } catch (const XBadClient& e) {
+            // TODO: disconnect handling is currently dispersed across both parseMessage() and
+            // handleData() functions, we should collect that to a single place
+
+            LOG((CLOG_ERR "protocol error from client: %s", e.what()));
+            disconnect();
+            return;
+        }
 
         // next message
         n = getStream()->read(code, 4);

src/lib/server/ClientProxyUnknown.cpp

@@ -118,6 +118,10 @@ ClientProxyUnknown::addStreamHandlers()
                             m_stream->getEventTarget(),
                             new TMethodEventJob<ClientProxyUnknown>(this,
                                 &ClientProxyUnknown::handleDisconnect));
+    m_events->adoptHandler(m_events->forIStream().inputFormatError(),
+                           m_stream->getEventTarget(),
+                           new TMethodEventJob<ClientProxyUnknown>(this,
+                                &ClientProxyUnknown::handleDisconnect));
     m_events->adoptHandler(m_events->forIStream().outputShutdown(),
                             m_stream->getEventTarget(),
                             new TMethodEventJob<ClientProxyUnknown>(this,
@@ -149,6 +153,8 @@ ClientProxyUnknown::removeHandlers()
                             m_stream->getEventTarget());
         m_events->removeHandler(m_events->forIStream().inputShutdown(),
                             m_stream->getEventTarget());
+        m_events->removeHandler(m_events->forIStream().inputFormatError(),
+                                m_stream->getEventTarget());
         m_events->removeHandler(m_events->forIStream().outputShutdown(),
                             m_stream->getEventTarget());
     }