296 lines
9.0 KiB
Go
296 lines
9.0 KiB
Go
// Package smtp provides a zgrab2 module that scans for SMTP mail
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// servers.
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// Default Port: 25 (TCP)
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//
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// The --smtps command tells the scanner to wrap the entire connection
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// in a TLS session.
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//
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// The --send-ehlo and --send-helo flags tell the scanner to first send
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// the EHLO/HELO command; if a --ehlo-domain or --helo-domain is present
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// that domain will be used, otherwise it is omitted.
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// The EHLO and HELO flags are mutually exclusive.
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//
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// The --send-help flag tells the scanner to send a HELP command.
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//
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// The --starttls flag tells the scanner to send the STARTTLS command,
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// and then negotiate a TLS connection.
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// The scanner uses the standard TLS flags for the handshake.
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//
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// The --send-quit flag tells the scanner to send a QUIT command.
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//
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// So, if no flags are specified, the scanner simply reads the banner
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// returned by the server and disconnects.
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//
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// The output contains the banner and the responses to any commands that
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// were sent, and if --starttls or --smtps was sent, the standard TLS logs.
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package smtp
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import (
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"errors"
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"fmt"
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"strconv"
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log "github.com/sirupsen/logrus"
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"github.com/zmap/zgrab2"
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)
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// ErrInvalidResponse is returned when the server returns an invalid or unexpected response.
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var ErrInvalidResponse = errors.New("invalid response")
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// ScanResults instances are returned by the module's Scan function.
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type ScanResults struct {
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// Banner is the string sent by the server immediately after connecting.
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Banner string `json:"banner,omitempty"`
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// HELO is the server's response to the HELO command, if one is sent.
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HELO string `json:"helo,omitempty"`
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// EHLO is the server's response to the EHLO command, if one is sent.
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EHLO string `json:"ehlo,omitempty"`
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// HELP is the server's response to the HELP command, if it is sent.
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HELP string `json:"help,omitempty"`
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// StartTLS is the server's response to the STARTTLS command, if it is sent.
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StartTLS string `json:"starttls,omitempty"`
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// QUIT is the server's response to the QUIT command, if it is sent.
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QUIT string `json:"quit,omitempty"`
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// TLSLog is the standard TLS log, if STARTTLS is sent.
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TLSLog *zgrab2.TLSLog `json:"tls,omitempty"`
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}
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// Flags holds the command-line configuration for the HTTP scan module.
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// Populated by the framework.
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type Flags struct {
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zgrab2.BaseFlags
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zgrab2.TLSFlags
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// SendHELO indicates that the EHLO command should be set.
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SendEHLO bool `long:"send-ehlo" description:"Send the EHLO command; use --ehlo-domain to set a domain."`
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// SendEHLO indicates that the EHLO command should be set.
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SendHELO bool `long:"send-helo" description:"Send the EHLO command; use --helo-domain to set a domain."`
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// SendHELP indicates that the client should send the HELP command (after HELO/EHLO).
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SendHELP bool `long:"send-help" description:"Send the HELP command"`
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// SendQUIT indicates that the QUIT command should be set.
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SendQUIT bool `long:"send-quit" description:"Send the QUIT command before closing."`
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// HELODomain is the domain the client should send in the HELO command.
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HELODomain string `long:"helo-domain" description:"Set the domain to use with the HELO command. Implies --send-helo."`
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// EHLODomain is the domain the client should send in the HELO command.
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EHLODomain string `long:"ehlo-domain" description:"Set the domain to use with the EHLO command. Implies --send-ehlo."`
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// SMTPSecure indicates that the entire transaction should be wrapped in a TLS session.
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SMTPSecure bool `long:"smtps" description:"Perform a TLS handshake immediately upon connecting."`
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// StartTLS indicates that the client should attempt to update the connection to TLS.
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StartTLS bool `long:"starttls" description:"Send STARTTLS before negotiating"`
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// Verbose indicates that there should be more verbose logging.
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Verbose bool `long:"verbose" description:"More verbose logging, include debug fields in the scan results"`
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}
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// Module implements the zgrab2.Module interface.
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type Module struct {
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}
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// Scanner implements the zgrab2.Scanner interface.
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type Scanner struct {
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config *Flags
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}
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// RegisterModule registers the zgrab2 module.
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func RegisterModule() {
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var module Module
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_, err := zgrab2.AddCommand("smtp", "smtp", "Probe for smtp", 25, &module)
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if err != nil {
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log.Fatal(err)
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}
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}
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// NewFlags returns a default Flags object.
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func (module *Module) NewFlags() interface{} {
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return new(Flags)
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}
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// NewScanner returns a new Scanner instance.
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func (module *Module) NewScanner() zgrab2.Scanner {
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return new(Scanner)
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}
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// Validate checks that the flags are valid.
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// On success, returns nil.
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// On failure, returns an error instance describing the error.
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func (flags *Flags) Validate(args []string) error {
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if flags.StartTLS && flags.SMTPSecure {
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log.Errorln("Cannot specify both --smtps and --starttls")
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return zgrab2.ErrInvalidArguments
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}
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if flags.EHLODomain != "" {
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flags.SendEHLO = true
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}
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if flags.HELODomain != "" {
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flags.SendHELO = true
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}
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if flags.SendHELO && flags.SendEHLO {
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log.Errorln("Cannot provide both EHLO and HELO")
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return zgrab2.ErrInvalidArguments
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}
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return nil
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}
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// Help returns the module's help string.
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func (flags *Flags) Help() string {
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return ""
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}
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// Init initializes the Scanner.
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func (scanner *Scanner) Init(flags zgrab2.ScanFlags) error {
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f, _ := flags.(*Flags)
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scanner.config = f
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return nil
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}
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// InitPerSender initializes the scanner for a given sender.
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func (scanner *Scanner) InitPerSender(senderID int) error {
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return nil
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}
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// GetName returns the Scanner name defined in the Flags.
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func (scanner *Scanner) GetName() string {
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return scanner.config.Name
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}
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// GetTrigger returns the Trigger defined in the Flags.
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func (scanner *Scanner) GetTrigger() string {
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return scanner.config.Trigger
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}
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// Protocol returns the protocol identifier of the scan.
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func (scanner *Scanner) Protocol() string {
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return "smtp"
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}
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// GetPort returns the port being scanned.
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func (scanner *Scanner) GetPort() uint {
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return scanner.config.Port
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}
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func getSMTPCode(response string) (int, error) {
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if len(response) < 5 {
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return 0, ErrInvalidResponse
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}
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ret, err := strconv.Atoi(response[0:3])
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if err != nil {
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return 0, ErrInvalidResponse
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}
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return ret, nil
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}
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// Get a command with an optional argument (so if the argument is absent, there is no trailing space)
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func getCommand(cmd string, arg string) string {
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if arg == "" {
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return cmd
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}
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return cmd + " " + arg
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}
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// Scan performs the SMTP scan.
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// 1. Open a TCP connection to the target port (default 25).
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// 2. If --smtps is set, perform a TLS handshake.
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// 3. Read the banner.
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// 4. If --send-ehlo or --send-helo is sent, send the corresponding EHLO
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// or HELO command.
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// 5. If --send-help is sent, send HELP, read the result.
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// 6. If --starttls is sent, send STARTTLS, read the result, negotiate a
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// TLS connection.
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// 7. If --send-quit is sent, send QUIT and read the result.
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// 8. Close the connection.
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func (scanner *Scanner) Scan(target zgrab2.ScanTarget) (zgrab2.ScanStatus, interface{}, error) {
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c, err := target.Open(&scanner.config.BaseFlags)
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if err != nil {
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return zgrab2.TryGetScanStatus(err), nil, err
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}
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defer c.Close()
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result := &ScanResults{}
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if scanner.config.SMTPSecure {
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tlsConn, err := scanner.config.TLSFlags.GetTLSConnection(c)
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if err != nil {
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return zgrab2.TryGetScanStatus(err), nil, err
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}
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result.TLSLog = tlsConn.GetLog()
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if err := tlsConn.Handshake(); err != nil {
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return zgrab2.TryGetScanStatus(err), result, err
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}
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c = tlsConn
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}
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conn := Connection{Conn: c}
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banner, err := conn.ReadResponse()
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if err != nil {
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if !scanner.config.SMTPSecure {
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result = nil
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}
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return zgrab2.TryGetScanStatus(err), result, err
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}
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result.Banner = banner
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if scanner.config.SendHELO {
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ret, err := conn.SendCommand(getCommand("HELO", scanner.config.HELODomain))
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if err != nil {
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return zgrab2.TryGetScanStatus(err), result, err
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}
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result.HELO = ret
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}
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if scanner.config.SendEHLO {
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ret, err := conn.SendCommand(getCommand("EHLO", scanner.config.EHLODomain))
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if err != nil {
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return zgrab2.TryGetScanStatus(err), result, err
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}
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result.EHLO = ret
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}
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if scanner.config.SendHELP {
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ret, err := conn.SendCommand("HELP")
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if err != nil {
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return zgrab2.TryGetScanStatus(err), result, err
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}
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result.HELP = ret
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}
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if scanner.config.StartTLS {
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ret, err := conn.SendCommand("STARTTLS")
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if err != nil {
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return zgrab2.TryGetScanStatus(err), result, err
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}
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result.StartTLS = ret
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code, err := getSMTPCode(ret)
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if err != nil {
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return zgrab2.TryGetScanStatus(err), result, err
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}
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if code < 200 || code >= 300 {
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return zgrab2.SCAN_APPLICATION_ERROR, result, fmt.Errorf("SMTP error code %d returned from STARTTLS command (%s)", code, ret)
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}
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tlsConn, err := scanner.config.TLSFlags.GetTLSConnection(conn.Conn)
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if err != nil {
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return zgrab2.TryGetScanStatus(err), result, err
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}
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result.TLSLog = tlsConn.GetLog()
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if err := tlsConn.Handshake(); err != nil {
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return zgrab2.TryGetScanStatus(err), result, err
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}
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conn.Conn = tlsConn
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}
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if scanner.config.SendQUIT {
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ret, err := conn.SendCommand("QUIT")
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if err != nil {
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if err != nil {
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return zgrab2.TryGetScanStatus(err), nil, err
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}
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}
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result.QUIT = ret
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}
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return zgrab2.SCAN_SUCCESS, result, nil
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}
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