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server.go
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server.go
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package main
import (
"context"
"crypto/rsa"
"database/sql"
"encoding/json"
"errors"
"fmt"
"net"
"os"
"strings"
"sync"
"text/template"
"time"
"github.com/google/go-github/v29/github"
"golang.org/x/crypto/ssh"
)
var termTmpl = template.Must(template.New("termTmpl").Parse(strings.Replace(`
+---------------------------------------------------------------------+
| |
| _o/ Hello {{ .Name }}!
| |
| |
| Did you know that ssh sends all your public keys to any server |
| it tries to authenticate to? |
| |
| That's how we know you are @{{ .User }} on GitHub!
| |
| Ah, maybe what you didn't know is that GitHub publishes all users' |
| ssh public keys and Ben (benjojo.co.uk) grabbed them all. |
| |
| That's pretty handy at times :) for example your key is at |
| https://github.com/{{ .User }}.keys
| |
| |
| P.S. This whole thingy is Open Source! (And written in Go!) |
| https://github.com/FiloSottile/whoami.filippo.io |
| |
| -- @FiloSottile (https://twitter.com/FiloSottile) |
| |
+---------------------------------------------------------------------+
`, "\n", "\n\r", -1)))
var failedMsg = []byte(strings.Replace(`
+---------------------------------------------------------------------+
| |
| _o/ Hello! |
| |
| |
| Did you know that ssh sends all your public keys to any server |
| it tries to authenticate to? You can see yours echoed below. |
| |
| We tried to use that to find your GitHub username, but we |
| couldn't :( maybe you don't even have GitHub ssh keys, do you? |
| |
| By the way, did you know that GitHub publishes all users' |
| ssh public keys and Ben (benjojo.co.uk) grabbed them all? |
| |
| That's pretty handy at times :) But not this time :( |
| |
| |
| P.S. This whole thingy is Open Source! (And written in Go!) |
| https://github.com/FiloSottile/whoami.filippo.io |
| |
| -- @FiloSottile (https://twitter.com/FiloSottile) |
| |
+---------------------------------------------------------------------+
`, "\n", "\n\r", -1))
var agentMsg = []byte(strings.Replace(`
***** WARNING ***** WARNING *****
You have SSH agent forwarding turned (universally?) on. That
is a VERY BAD idea. For example right now I have access to your
agent and I can use your keys however I want as long as you are
connected. I'm a good guy and I won't do anything, but ANY SERVER
YOU LOG IN TO AND ANYONE WITH ROOT ON THOSE SERVERS CAN LOGIN AS
YOU ANYWHERE.
Read more: http://git.io/vO2A6
`, "\n", "\n\r", -1))
var x11Msg = []byte(strings.Replace(`
***** WARNING ***** WARNING *****
You have X11 forwarding turned (universally?) on. That
is a VERY BAD idea. For example right now I have access to your
X11 server and I can access your desktop as long as you are
connected. I'm a good guy and I won't do anything, but ANY SERVER
YOU LOG IN TO AND ANYONE WITH ROOT ON THOSE SERVERS CAN SNIFF
YOUR KEYSTROKES AND ACCESS YOUR WINDOWS.
Read more: http://www.hackinglinuxexposed.com/articles/20040705.html
`, "\n", "\n\r", -1))
var roamingMsg = []byte(strings.Replace(`
***** WARNING ***** WARNING *****
You have roaming turned on. If you are using OpenSSH, that most likely
means you are vulnerable to the CVE-2016-0777 information leak.
THIS MEANS THAT ANY SERVER YOU CONNECT TO MIGHT OBTAIN YOUR PRIVATE KEYS.
Add "UseRoaming no" to the "Host *" section of your ~/.ssh/config or
/etc/ssh/ssh_config file, rotate keys and update ASAP.
Read more: https://www.qualys.com/2016/01/14/cve-2016-0777-cve-2016-0778/openssh-cve-2016-0777-cve-2016-0778.txt
`, "\n", "\n\r", -1))
type sessionInfo struct {
User string
Keys []ssh.PublicKey
}
type Server struct {
githubClient *github.Client
sshConfig *ssh.ServerConfig
newQuery *sql.Stmt
legacyQuery *sql.Stmt
mu sync.RWMutex
sessionInfo map[string]sessionInfo
}
func (s *Server) PublicKeyCallback(conn ssh.ConnMetadata, key ssh.PublicKey) (*ssh.Permissions, error) {
s.mu.Lock()
si := s.sessionInfo[string(conn.SessionID())]
si.User = conn.User()
si.Keys = append(si.Keys, key)
s.sessionInfo[string(conn.SessionID())] = si
s.mu.Unlock()
// Never succeed a key, or we might not see the next. See KeyboardInteractiveCallback.
return nil, errors.New("")
}
func (s *Server) KeyboardInteractiveCallback(ssh.ConnMetadata, ssh.KeyboardInteractiveChallenge) (*ssh.Permissions, error) {
// keyboard-interactive is tried when all public keys failed, and
// since it's server-driven we can just pass without user
// interaction to let the user in once we got all the public keys
return nil, nil
}
type logEntry struct {
Timestamp string
Username string
RequestTypes []string
Error string
KeysOffered []string
GitHub string
ClientVersion string
}
func (s *Server) Handle(nConn net.Conn) {
le := &logEntry{Timestamp: time.Now().Format(time.RFC3339)}
defer json.NewEncoder(os.Stdout).Encode(le)
conn, chans, reqs, err := ssh.NewServerConn(nConn, s.sshConfig)
if err != nil {
le.Error = "Handshake failed: " + err.Error()
return
}
defer func() {
s.mu.Lock()
delete(s.sessionInfo, string(conn.SessionID()))
s.mu.Unlock()
time.Sleep(500 * time.Millisecond)
conn.Close()
}()
roaming := false
go func(in <-chan *ssh.Request) {
for req := range in {
le.RequestTypes = append(le.RequestTypes, req.Type)
if req.Type == "roaming@appgate.com" {
roaming = true
}
if req.WantReply {
req.Reply(false, nil)
}
}
}(reqs)
s.mu.RLock()
si := s.sessionInfo[string(conn.SessionID())]
s.mu.RUnlock()
le.Username = conn.User()
le.ClientVersion = fmt.Sprintf("%x", conn.ClientVersion())
for _, key := range si.Keys {
le.KeysOffered = append(le.KeysOffered, string(ssh.MarshalAuthorizedKey(key)))
}
for newChannel := range chans {
if newChannel.ChannelType() != "session" {
newChannel.Reject(ssh.UnknownChannelType, "unknown channel type")
continue
}
channel, requests, err := newChannel.Accept()
if err != nil {
le.Error = "Channel accept failed: " + err.Error()
return
}
defer channel.Close()
agentFwd, x11 := false, false
reqLock := &sync.Mutex{}
reqLock.Lock()
timeout := time.AfterFunc(30*time.Second, func() { reqLock.Unlock() })
go func(in <-chan *ssh.Request) {
for req := range in {
le.RequestTypes = append(le.RequestTypes, req.Type)
ok := false
switch req.Type {
case "shell":
fallthrough
case "pty-req":
ok = true
// "auth-agent-req@openssh.com" and "x11-req" always arrive
// before the "pty-req", so we can go ahead now
if timeout.Stop() {
reqLock.Unlock()
}
case "auth-agent-req@openssh.com":
agentFwd = true
case "x11-req":
x11 = true
}
if req.WantReply {
req.Reply(ok, nil)
}
}
}(requests)
reqLock.Lock()
if agentFwd {
channel.Write(agentMsg)
}
if x11 {
channel.Write(x11Msg)
}
if roaming {
channel.Write(roamingMsg)
}
user, err := s.findUser(si.Keys)
if err != nil {
le.Error = "findUser failed: " + err.Error()
return
}
if user == "" {
channel.Write(failedMsg)
for _, key := range si.Keys {
channel.Write(ssh.MarshalAuthorizedKey(key))
channel.Write([]byte("\r"))
}
channel.Write([]byte("\n\r"))
return
}
le.GitHub = user
name, err := s.getUserName(user)
if err != nil {
le.Error = "getUserName failed: " + err.Error()
return
}
termTmpl.Execute(channel, struct{ Name, User string }{name, user})
return
}
}
func (s *Server) findUser(keys []ssh.PublicKey) (string, error) {
for _, pk := range keys {
var user string
key := strings.TrimSpace(string(ssh.MarshalAuthorizedKey(pk)))
err := s.newQuery.QueryRow(key).Scan(&user)
if err == sql.ErrNoRows && pk.Type() == ssh.KeyAlgoRSA {
// Try the legacy database.
k := pk.(ssh.CryptoPublicKey).CryptoPublicKey().(*rsa.PublicKey)
err = s.legacyQuery.QueryRow(k.N.String()).Scan(&user)
}
if err == sql.ErrNoRows {
continue
}
if err != nil {
return "", err
}
return user, nil
}
return "", nil
}
func (s *Server) getUserName(user string) (string, error) {
u, _, err := s.githubClient.Users.Get(context.TODO(), user)
if err != nil {
return "", err
}
if u.Name == nil {
return "@" + user, nil
}
return *u.Name, nil
}