Head and Tail commands

client/command/filesystem/cat.go

@@ -56,8 +56,9 @@ func CatCmd(cmd *cobra.Command, con *console.SliverConsoleClient, args []string)
 	ctrl := make(chan bool)
 	con.SpinUntil(fmt.Sprintf("Downloading %s ...", filePath), ctrl)
 	download, err := con.Rpc.Download(context.Background(), &sliverpb.DownloadReq{
-		Request: con.ActiveTarget.Request(cmd),
-		Path:    filePath,
+		Request:          con.ActiveTarget.Request(cmd),
+		RestrictedToFile: true,
+		Path:             filePath,
 	})
 	ctrl <- true
 	<-ctrl

client/command/filesystem/download.go

@@ -51,9 +51,10 @@ func DownloadCmd(cmd *cobra.Command, con *console.SliverConsoleClient, args []st
 	ctrl := make(chan bool)
 	con.SpinUntil(fmt.Sprintf("Downloading %s ...", remotePath), ctrl)
 	download, err := con.Rpc.Download(context.Background(), &sliverpb.DownloadReq{
-		Request: con.ActiveTarget.Request(cmd),
-		Path:    remotePath,
-		Recurse: recurse,
+		Request:          con.ActiveTarget.Request(cmd),
+		Path:             remotePath,
+		Recurse:          recurse,
+		RestrictedToFile: false,
 	})
 	ctrl <- true
 	<-ctrl
@@ -119,7 +120,12 @@ func HandleDownloadResponse(download *sliverpb.Download, cmd *cobra.Command, arg
 	}
 
 	remotePath := args[0]
-	localPath := args[1]
+	var localPath string
+	if len(args) == 1 {
+		localPath = "."
+	} else {
+		localPath = args[1]
+	}
 	saveLoot, _ := cmd.Flags().GetBool("loot")
 
 	if download.ReadFiles == 0 {

client/command/filesystem/head.go

@@ -0,0 +1,127 @@
+package filesystem
+
+/*
+	Sliver Implant Framework
+	Copyright (C) 2023  Bishop Fox
+
+	This program is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with this program.  If not, see <https://www.gnu.org/licenses/>.
+*/
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/bishopfox/sliver/client/console"
+	"github.com/bishopfox/sliver/protobuf/clientpb"
+	"github.com/bishopfox/sliver/protobuf/sliverpb"
+	"github.com/spf13/cobra"
+	"google.golang.org/protobuf/proto"
+)
+
+func HeadCmd(cmd *cobra.Command, con *console.SliverConsoleClient, args []string, head bool) {
+	session, beacon := con.ActiveTarget.GetInteractive()
+	if session == nil && beacon == nil {
+		return
+	}
+
+	var filePath string
+	var fetchBytes bool
+	var fetchSize int64
+	var operationName string
+	var download *sliverpb.Download
+	var err error
+
+	if len(args) > 0 {
+		filePath = args[0]
+	}
+	if filePath == "" {
+		con.PrintErrorf("Missing parameter: file name\n")
+		return
+	}
+
+	if cmd.Flags().Changed("bytes") {
+		fetchBytes = true
+		fetchSize, _ = cmd.Flags().GetInt64("bytes")
+		if fetchSize < 0 {
+			// Cannot fetch a negative number of bytes
+			con.PrintErrorf("The number of bytes specified must be positive.")
+			return
+		}
+		if fetchSize == 1 {
+			operationName = "byte"
+		} else {
+			operationName = "bytes"
+		}
+	} else if cmd.Flags().Changed("lines") {
+		fetchBytes = false
+		fetchSize, _ = cmd.Flags().GetInt64("lines")
+		if fetchSize < 0 {
+			// Cannot fetch a negative number of lines
+			con.PrintErrorf("The number of lines specified must be positive.")
+			return
+		}
+		if fetchSize == 1 {
+			operationName = "line"
+		} else {
+			operationName = "lines"
+		}
+	} else {
+		con.PrintErrorf("A number of bytes or a number of lines must be specified.")
+		return
+	}
+
+	ctrl := make(chan bool)
+	con.SpinUntil(fmt.Sprintf("Retrieving %d %s from %s ...", fetchSize, operationName, filePath), ctrl)
+
+	// A tail is a negative head
+	if !head {
+		fetchSize *= -1
+	}
+
+	if fetchBytes {
+		download, err = con.Rpc.Download(context.Background(), &sliverpb.DownloadReq{
+			Request:          con.ActiveTarget.Request(cmd),
+			Path:             filePath,
+			MaxBytes:         fetchSize,
+			RestrictedToFile: true,
+		})
+	} else {
+		download, err = con.Rpc.Download(context.Background(), &sliverpb.DownloadReq{
+			Request:          con.ActiveTarget.Request(cmd),
+			Path:             filePath,
+			MaxLines:         fetchSize,
+			RestrictedToFile: true,
+		})
+	}
+
+	ctrl <- true
+	<-ctrl
+	if err != nil {
+		con.PrintErrorf("%s\n", err)
+		return
+	}
+	if download.Response != nil && download.Response.Async {
+		con.AddBeaconCallback(download.Response.TaskID, func(task *clientpb.BeaconTask) {
+			err = proto.Unmarshal(task.Response, download)
+			if err != nil {
+				con.PrintErrorf("Failed to decode response %s\n", err)
+				return
+			}
+			PrintCat(download, cmd, con)
+		})
+		con.PrintAsyncResponse(download.Response)
+	} else {
+		PrintCat(download, cmd, con)
+	}
+}

client/command/help/long-help.go

@@ -60,6 +60,8 @@ var (
 		consts.CatStr:              catHelp,
 		consts.DownloadStr:         downloadHelp,
 		consts.GrepStr:             grepHelp,
+		consts.HeadStr:             headHelp,
+		consts.TailStr:             tailHelp,
 		consts.UploadStr:           uploadHelp,
 		consts.MkdirStr:            mkdirHelp,
 		consts.RmStr:               rmHelp,
@@ -322,6 +324,12 @@ Downloads can be filtered using the following patterns:
 If you need to match a special character (*, ?, '-', '[', ']', '\\'), place '\\' in front of it (example: \\?).
 On Windows, escaping is disabled. Instead, '\\' is treated as path separator.`
 
+	headHelp = `[[.Bold]]Command:[[.Normal]] head [--bytes/-b <number of bytes>] [--lines/-l <number of lines>] <remote path> 
+	[[.Bold]]About:[[.Normal]] Fetch the first number of bytes or lines from a remote file and display it to stdout.`
+
+	tailHelp = `[[.Bold]]Command:[[.Normal]] tail [--bytes/-b <number of bytes>] [--lines/-l <number of lines>] <remote path> 
+	[[.Bold]]About:[[.Normal]] Fetch the last number of bytes or lines from a remote file and display it to stdout.`
+
 	uploadHelp = `[[.Bold]]Command:[[.Normal]] upload [local src] <remote dst>
 [[.Bold]]About:[[.Normal]] Upload a file to the remote system.`
 

client/command/sliver.go

@@ -968,6 +968,62 @@ func SliverCommands(con *client.SliverConsoleClient) console.Commands {
 			carapace.ActionValues().Usage("remote path / file to search in"),
 		)
 
+		headCmd := &cobra.Command{
+			Use:   consts.HeadStr,
+			Short: "Grab the first number of bytes or lines from a file",
+			Long:  help.GetHelpFor([]string{consts.HeadStr}),
+			Args:  cobra.ExactArgs(1),
+			Run: func(cmd *cobra.Command, args []string) {
+				/*
+					The last argument tells head if the user requested the head or tail of the file
+					True means head, false means tail
+				*/
+				filesystem.HeadCmd(cmd, con, args, true)
+			},
+			GroupID: consts.FilesystemHelpGroup,
+		}
+		sliver.AddCommand(headCmd)
+		Flags("", false, headCmd, func(f *pflag.FlagSet) {
+			f.BoolP("colorize-output", "c", false, "colorize output")
+			f.BoolP("hex", "x", false, "display as a hex dump")
+			f.BoolP("loot", "X", false, "save output as loot")
+			f.StringP("name", "n", "", "name to assign loot (optional)")
+			f.StringP("type", "T", "", "force a specific loot type (file/cred) if looting (optional)")
+			f.StringP("file-type", "F", "", "force a specific file type (binary/text) if looting (optional)")
+			f.Int64P("timeout", "t", defaultTimeout, "grpc timeout in seconds")
+			f.Int64P("bytes", "b", 0, "Grab the first number of bytes from the file")
+			f.Int64P("lines", "l", 0, "Grab the first number of lines from the file")
+		})
+		carapace.Gen(headCmd).PositionalCompletion(carapace.ActionValues().Usage("path to the file to print"))
+
+		tailCmd := &cobra.Command{
+			Use:   consts.TailStr,
+			Short: "Grab the last number of bytes or lines from a file",
+			Long:  help.GetHelpFor([]string{consts.TailStr}),
+			Args:  cobra.ExactArgs(1),
+			Run: func(cmd *cobra.Command, args []string) {
+				/*
+					The last argument tells head if the user requested the head or tail of the file
+					True means head, false means tail
+				*/
+				filesystem.HeadCmd(cmd, con, args, false)
+			},
+			GroupID: consts.FilesystemHelpGroup,
+		}
+		sliver.AddCommand(tailCmd)
+		Flags("", false, tailCmd, func(f *pflag.FlagSet) {
+			f.BoolP("colorize-output", "c", false, "colorize output")
+			f.BoolP("hex", "x", false, "display as a hex dump")
+			f.BoolP("loot", "X", false, "save output as loot")
+			f.StringP("name", "n", "", "name to assign loot (optional)")
+			f.StringP("type", "T", "", "force a specific loot type (file/cred) if looting (optional)")
+			f.StringP("file-type", "F", "", "force a specific file type (binary/text) if looting (optional)")
+			f.Int64P("timeout", "t", defaultTimeout, "grpc timeout in seconds")
+			f.Int64P("bytes", "b", 0, "Grab the last number of bytes from the file")
+			f.Int64P("lines", "l", 0, "Grab the last number of lines from the file")
+		})
+		carapace.Gen(tailCmd).PositionalCompletion(carapace.ActionValues().Usage("path to the file to print"))
+
 		uploadCmd := &cobra.Command{
 			Use:   consts.UploadStr,
 			Short: "Upload a file",

client/constants/constants.go

@@ -206,6 +206,8 @@ const (
 	PwdStr      = "pwd"
 	CatStr      = "cat"
 	DownloadStr = "download"
+	HeadStr     = "head"
+	TailStr     = "tail"
 	GrepStr     = "grep"
 	UploadStr   = "upload"
 	IfconfigStr = "ifconfig"

implant/sliver/handlers/handlers.go

@@ -448,19 +448,79 @@ func pwdHandler(data []byte, resp RPCResponse) {
 	resp(data, err)
 }
 
-func prepareDownload(path string, filter string, recurse bool) ([]byte, bool, int, int, error) {
+func prepareDownload(path string, filter string, recurse bool, maxBytes int64, maxLines int64) ([]byte, bool, int, int, error) {
 	/*
 		Combine the path and filter to see if the user wants
 		to download a single file
 	*/
+	var rawData []byte
+	var err error
+
 	fileInfo, err := os.Stat(path + filter)
 
 	if err == nil && !fileInfo.IsDir() {
 		// Then this is a single file
-		rawData, err := os.ReadFile(path + filter)
+		fileHandle, err := os.Open(path + filter)
 		if err != nil {
 			// Then we could not read the file
 			return nil, false, 0, 1, err
+		}
+		defer fileHandle.Close()
+
+		if maxBytes != 0 {
+			var readFirst bool = maxBytes > 0
+			if readFirst {
+				rawData = make([]byte, maxBytes)
+				_, err = fileHandle.Read(rawData)
+			} else {
+				rawData = make([]byte, maxBytes*-1)
+				var bytesToRead int64 = 0
+				if fileInfo.Size()+maxBytes < 0 {
+					bytesToRead = 0
+				} else {
+					bytesToRead = fileInfo.Size() + maxBytes
+				}
+				_, err = fileHandle.ReadAt(rawData, bytesToRead)
+			}
+
+		} else if maxLines != 0 {
+			var linesRead int64 = 0
+			var lines []string
+			var readFirst bool = true
+
+			if maxLines < 0 {
+				maxLines *= -1
+				readFirst = false
+			}
+
+			fileScanner := bufio.NewScanner(fileHandle)
+			for fileScanner.Scan() {
+				lines = append(lines, fileScanner.Text())
+				linesRead += 1
+				if linesRead == maxLines && readFirst {
+					break
+				}
+			}
+			err = fileScanner.Err()
+			if err == nil {
+				if readFirst {
+					rawData = []byte(strings.Join(lines, "\n"))
+				} else {
+					linePosition := int64(len(lines)) - maxLines
+					if linePosition < 0 {
+						linePosition = 0
+					}
+					rawData = []byte(strings.Join(lines[linePosition:], "\n"))
+				}
+			}
+		} else {
+			// Read the entire file
+			rawData = make([]byte, fileInfo.Size())
+			_, err = fileHandle.Read(rawData)
+		}
+		if err != nil && err != io.EOF {
+			// Then we could not read the file
+			return nil, false, 0, 1, err
 		} else {
 			return rawData, false, 1, 0, nil
 		}
@@ -498,11 +558,29 @@ func downloadHandler(data []byte, resp RPCResponse) {
 	if pathIsDirectory(target) {
 		// Even if the implant is running on Windows, Go can deal with "/" as a path separator
 		target += "/"
+		if downloadReq.RestrictedToFile {
+			/*
+				The user has asked to perform a download operation that should only be allowed on
+				files, and this is a directory. We should let them know.
+			*/
+			err = fmt.Errorf("cannot complete command because target %s is a directory", target)
+			// {{if .Config.Debug}}
+			log.Printf("error completing download command: %v", err)
+			// {{end}}
+			download = &sliverpb.Download{Path: target, Exists: false, ReadFiles: 0, UnreadableFiles: 0}
+			download.Response = &commonpb.Response{
+				Err: fmt.Sprintf("%v", err),
+			}
+
+			data, _ = proto.Marshal(download)
+			resp(data, err)
+			return
+		}
 	}
 
 	path, filter := determineDirPathFilter(target)
 
-	rawData, isDir, readFiles, unreadableFiles, err := prepareDownload(path, filter, downloadReq.Recurse)
+	rawData, isDir, readFiles, unreadableFiles, err := prepareDownload(path, filter, downloadReq.Recurse, downloadReq.MaxBytes, downloadReq.MaxLines)
 
 	if err != nil {
 		if isDir {