fixed issue #224

cmd/amass/enum.go

@@ -162,23 +162,20 @@ func runEnumCommand(clArgs []string) {
 		commandUsage(enumUsageMsg, enumCommand, enumBuf)
 		return
 	}
+	// Check if the user has requested the data source names
+	if args.Options.ListSources {
+		for _, name := range GetAllSourceNames() {
+			g.Println(name)
+		}
+		return
+	}
 
 	if len(args.AltWordListMask) > 0 {
 		args.AltWordList = utils.UniqueAppend(args.AltWordList, args.AltWordListMask...)
 	}
 	if len(args.BruteWordListMask) > 0 {
 		args.BruteWordList = utils.UniqueAppend(args.BruteWordList, args.BruteWordListMask...)
 	}
-
-	// Check if the user has requested the data source names
-	if args.Options.ListSources {
-		e := enum.NewEnumeration()
-
-		for _, name := range e.GetAllSourceNames() {
-			g.Println(name)
-		}
-		return
-	}
 	// Some input validation
 	if args.Options.Passive && (args.Options.IPs || args.Options.IPv4 || args.Options.IPv6) {
 		r.Fprintln(color.Error, "IP addresses cannot be provided without DNS resolution")
@@ -197,10 +194,15 @@ func runEnumCommand(clArgs []string) {
 	// Seed the default pseudo-random number generator
 	rand.Seed(time.Now().UTC().UnixNano())
 
-	rLog, wLog := io.Pipe()
 	e := enum.NewEnumeration()
-	e.Config.Log = log.New(wLog, "", log.Lmicroseconds)
+	if e == nil {
+		r.Fprintf(color.Error, "%s\n", "No DNS resolvers passed the sanity check")
+		os.Exit(1)
+	}
 
+	rLog, wLog := io.Pipe()
+	e.Config.Log = log.New(wLog, "", log.Lmicroseconds)
+
 	// Check if a configuration file was provided, and if so, load the settings
 	if f, err := config.AcquireConfig(args.Filepaths.Directory, args.Filepaths.ConfigFile, e.Config); err == nil {
 		// Check if a config file was provided that has DNS resolvers specified

cmd/amass/intel.go

@@ -159,10 +159,15 @@ func runIntelCommand(clArgs []string) {
 		os.Exit(1)
 	}
 
-	rLog, wLog := io.Pipe()
 	ic := intel.NewIntelCollection()
-	ic.Config.Log = log.New(wLog, "", log.Lmicroseconds)
+	if ic == nil {
+		r.Fprintf(color.Error, "%s\n", "No DNS resolvers passed the sanity check")
+		os.Exit(1)
+	}
 
+	rLog, wLog := io.Pipe()
+	ic.Config.Log = log.New(wLog, "", log.Lmicroseconds)
+
 	// Check if a configuration file was provided, and if so, load the settings
 	if f, err := config.AcquireConfig(args.Filepaths.Directory, args.Filepaths.ConfigFile, ic.Config); err == nil {
 		// Check if a config file was provided that has DNS resolvers specified

enum/enum.go

@@ -81,6 +81,10 @@ func NewEnumeration() *Enumeration {
 		filter:      utils.NewStringFilter(),
 		outputQueue: new(utils.Queue),
 	}
+	if e.Pool == nil {
+		return nil
+	}
+
 	e.dataSources = sources.GetAllSources(e.Config, e.Bus, e.Pool)
 	return e
 }

intel/intel.go

@@ -46,7 +46,7 @@ type IntelCollection struct {
 
 // NewIntelCollection returns an initialized IntelCollection object that has not been started yet.
 func NewIntelCollection() *IntelCollection {
-	return &IntelCollection{
+	ic := &IntelCollection{
 		Config:     &config.Config{Log: log.New(ioutil.Discard, "", 0)},
 		Bus:        eb.NewEventBus(),
 		Pool:       resolvers.NewResolverPool(nil),
@@ -57,6 +57,10 @@ func NewIntelCollection() *IntelCollection {
 		domainChan: make(chan *requests.Output, 100),
 		activeChan: make(chan struct{}, 100),
 	}
+	if ic.Pool == nil {
+		return nil
+	}
+	return ic
 }
 
 // HostedDomains uses open source intelligence to discover root domain names in the target infrastructure.

resolvers/pool.go

@@ -76,7 +76,9 @@ func NewResolverPool(addrs []string) *ResolverPool {
 		addrs = DefaultPublicResolvers
 	}
 
-	rp.SetResolvers(addrs)
+	if err := rp.SetResolvers(addrs); err != nil {
+		return nil
+	}
 	return rp
 }
 
@@ -91,10 +93,15 @@ func (rp *ResolverPool) Stop() {
 // NextResolver returns a randomly selected Resolver from the pool that has availability.
 func (rp *ResolverPool) NextResolver() *Resolver {
 	var attempts int
-	max := len(rp.Resolvers)
+
 	for {
+		max := len(rp.Resolvers)
+		if max == 0 {
+			break
+		}
+
 		rnd := rand.Int()
-		r := rp.Resolvers[rnd%len(rp.Resolvers)]
+		r := rp.Resolvers[rnd%max]
 
 		if r.currentScore() > 50 && r.Available() {
 			return r
@@ -113,6 +120,7 @@ func (rp *ResolverPool) NextResolver() *Resolver {
 		attempts = 0
 		time.Sleep(time.Duration(randomInt(100, 1000)) * time.Millisecond)
 	}
+	return nil
 }
 
 // SetResolvers modifies the set of resolvers.
@@ -206,13 +214,20 @@ func (rp *ResolverPool) Resolve(name, qtype string, priority int) ([]requests.DN
 		num = 3
 	}
 
+	var queries int
 	ch := make(chan *resolveVote, num)
 	for i := 0; i < num; i++ {
-		go rp.queryResolver(rp.NextResolver(), ch, name, qtype, priority)
+		r := rp.NextResolver()
+		if r == nil {
+			break
+		}
+
+		go rp.queryResolver(r, ch, name, qtype, priority)
+		queries++
 	}
 
 	var votes []*resolveVote
-	for i := 0; i < num; i++ {
+	for i := 0; i < queries; i++ {
 		select {
 		case v := <-ch:
 			votes = append(votes, v)
@@ -265,7 +280,7 @@ func (rp *ResolverPool) ReverseDNS(addr string) (string, string, error) {
 func (rp *ResolverPool) performElection(votes []*resolveVote, name, qtype string) ([]requests.DNSAnswer, error) {
 	if len(votes) == 1 {
 		return votes[0].Answers, votes[0].Err
-	} else if votes[0].Err != nil && votes[1].Err != nil && votes[2].Err != nil {
+	} else if len(votes) < 3 || (votes[0].Err != nil && votes[1].Err != nil && votes[2].Err != nil) {
 		return []requests.DNSAnswer{}, votes[0].Err
 	}