Move LMS scoring under new Domain Heuristics

detection/dga/lms.go

@@ -4,16 +4,13 @@ import (
 	"strings"
 )
 
-// LmsScoreOfDomain calculates the mean longest meaningful substring of a domain. It follows some special rules to increase accuracy. It returns a value between 0 and 100, representing the length-based percentage of the meaningful substring.
+// LmsScoreOfDomain calculates the mean longest meaningful substring of a domain.
+// It follows some special rules to increase accuracy. It returns a value between
+// 0 and 100, representing the length-based percentage of the meaningful substring.
 func LmsScoreOfDomain(domain string) float64 {
 	var totalScore float64
 	domain = strings.ToLower(domain)
 	subjects := strings.Split(domain, ".")
-	// ignore the last two parts
-	if len(subjects) <= 3 {
-		return 100
-	}
-	subjects = subjects[:len(subjects)-3]
 	var totalLength int
 	for _, subject := range subjects {
 		totalLength += len(subject)
@@ -27,7 +24,9 @@ func LmsScoreOfDomain(domain string) float64 {
 	return totalScore
 }
 
-// LmsScore calculates the longest meaningful substring of a domain. It returns a value between 0 and 100, representing the length-based percentage of the meaningful substring.
+// LmsScore calculates the longest meaningful substring of a domain. It returns a
+// value between 0 and 100, representing the length-based percentage of the
+// meaningful substring.
 func LmsScore(subject string) float64 {
 	lmsStart := -1
 	lmsStop := -1

detection/dga/lms_test.go

@@ -5,8 +5,8 @@ import "testing"
 func TestLmsScoreOfDomain(t *testing.T) {
 	testDomain(t, "g.symcd.com.", 100, 100)
 	testDomain(t, "www.google.com.", 100, 100)
-	testDomain(t, "55ttt5.12abc3.test.com.", 50, 50)
-	testDomain(t, "mbtq6opnuodp34gcrma65fxacgxv5ukr7lq6xuhr4mhoibe7.yvqptrozfbnqyemchpovw3q5xwjibuxfsgb72mix3znhpfhc.i2n7jh2gadqaadck3zs3vg3hbv5pkmwzeay4gc75etyettbb.isi5mhmowtfriu33uxzmgvjur5g2p3tloynwohfrggee6fkn.meop7kqyd5gwxxa3.er.spotify.com.", 0, 30)
+	testDomain(t, "55ttt5.12abc3.test.com.", 68, 69)
+	testDomain(t, "mbtq6opnuodp34gcrma65fxacgxv5ukr7lq6xuhr4mhoibe7.yvqptrozfbnqyemchpovw3q5xwjibuxfsgb72mix3znhpfhc.i2n7jh2gadqaadck3zs3vg3hbv5pkmwzeay4gc75etyettbb.isi5mhmowtfriu33uxzmgvjur5g2p3tloynwohfrggee6fkn.meop7kqyd5gwxxa3.er.spotify.com.", 0, 31)
 }
 
 func testDomain(t *testing.T, domain string, min, max float64) {

firewall/master.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/safing/portmaster/detection/dga"
 	"github.com/safing/portmaster/netenv"
+	"golang.org/x/net/publicsuffix"
 
 	"github.com/safing/portbase/log"
 	"github.com/safing/portmaster/network"
@@ -59,7 +60,7 @@ func DecideOnConnection(ctx context.Context, conn *network.Connection, pkt packe
 		checkBypassPrevention,
 		checkFilterLists,
 		checkInbound,
-		checkLMSScore,
+		checkDomainHeuristics,
 		checkDefaultPermit,
 		checkAutoPermitRelated,
 		checkDefaultAction,
@@ -283,19 +284,63 @@ func checkFilterLists(ctx context.Context, conn *network.Connection, pkt packet.
 	return false
 }
 
-func checkLMSScore(ctx context.Context, conn *network.Connection, _ packet.Packet) bool {
+func checkDomainHeuristics(ctx context.Context, conn *network.Connection, _ packet.Packet) bool {
+	p := conn.Process().Profile()
+
+	if !p.DomainHeuristics() {
+		return false
+	}
+
 	if conn.Entity.Domain == "" {
 		return false
 	}
 
-	// check for possible DNS tunneling / data transmission
-	lms := dga.LmsScoreOfDomain(conn.Entity.Domain)
-	if lms < 10 {
-		log.Tracer(ctx).Warningf("nameserver: possible data tunnel by %s: %s has lms score of %f, returning nxdomain", conn.Process(), conn.Entity.Domain, lms)
-		conn.BlockWithContext("Possible data tunnel", conn.ReasonContext)
+	trimmedDomain := strings.TrimRight(conn.Entity.Domain, ".")
+	etld1, err := publicsuffix.EffectiveTLDPlusOne(trimmedDomain)
+	if err != nil {
+		// we don't apply any checks here and let the request through
+		// because a malformed domain-name will likely be dropped by
+		// checks better suited for that.
+		log.Tracer(ctx).Warningf("nameserver: failed to get eTLD+1: %s", err)
+		return false
+	}
 
+	domainToCheck := strings.Split(etld1, ".")[0]
+	score := dga.LmsScore(domainToCheck)
+	if score < 5 {
+		log.Tracer(ctx).Warningf(
+			"nameserver: possible data tunnel by %s in eTLD+1 %s: %s has an lms score of %.2f, returning nxdomain",
+			conn.Process(),
+			etld1,
+			domainToCheck,
+			score,
+		)
+		conn.Block("Possible data tunnel")
 		return true
 	}
+	log.Tracer(ctx).Infof("LMS score of eTLD+1 %s is %.2f", etld1, score)
+
+	// 100 is a somewhat arbitrary threshold to ensure we don't mess
+	// around with CDN domain names to early. They use short second-level
+	// domains that would trigger LMS checks but are to small to actually
+	// exfiltrate data.
+	if len(conn.Entity.Domain) > len(etld1)+100 {
+		domainToCheck = trimmedDomain[0:len(etld1)]
+		score := dga.LmsScoreOfDomain(domainToCheck)
+		if score < 10 {
+			log.Tracer(ctx).Warningf(
+				"nameserver: possible data tunnel by %s in subdomain %s: %s has an lms score of %.2f, returning nxdomain",
+				conn.Process(),
+				conn.Entity.Domain,
+				domainToCheck,
+				score,
+			)
+			conn.Block("Possible data tunnel")
+			return true
+		}
+		log.Tracer(ctx).Infof("LMS score of entire domain is %.2f", score)
+	}
+
 	return false
 }
 

profile/config.go

@@ -80,6 +80,10 @@ var (
 	cfgOptionRemoveBlockedDNS      config.IntOption // security level option
 	cfgOptionRemoveBlockedDNSOrder = 113
 
+	CfgOptionDomainHeuristicsKey   = "filter/domainHeuristics"
+	cfgOptionDomainHeuristics      config.IntOption // security level option
+	cfgOptionDomainHeuristicsOrder = 114
+
 	// Permanent Verdicts Order = 128
 )
 
@@ -378,6 +382,24 @@ Examples:
 	cfgOptionRemoveBlockedDNS = config.Concurrent.GetAsInt(CfgOptionRemoveBlockedDNSKey, int64(status.SecurityLevelsAll))
 	cfgIntOptions[CfgOptionRemoveBlockedDNSKey] = cfgOptionRemoveBlockedDNS
 
+	// Domain heuristics
+	err = config.Register(&config.Option{
+		Name:            "Enable Domain Heuristics",
+		Key:             CfgOptionDomainHeuristicsKey,
+		Description:     "Domain Heuristics checks for suspicious looking domain names and blocks them. Ths option currently targets domains generated by malware and DNS data tunnels.",
+		Order:           cfgOptionDomainHeuristicsOrder,
+		OptType:         config.OptTypeInt,
+		ExpertiseLevel:  config.ExpertiseLevelExpert,
+		ExternalOptType: "security level",
+		DefaultValue:    status.SecurityLevelsAll,
+		ValidationRegex: "^(0|4|6|7)$",
+	})
+	if err != nil {
+		return err
+	}
+	cfgOptionDomainHeuristics = config.Concurrent.GetAsInt(CfgOptionDomainHeuristicsKey, int64(status.SecurityLevelsAll))
+
+	// Bypass prevention
 	err = config.Register(&config.Option{
 		Name:            "Prevent Bypassing",
 		Key:             CfgOptionPreventBypassingKey,

profile/profile-layered.go

@@ -45,6 +45,7 @@ type LayeredProfile struct {
 	FilterSubDomains    config.BoolOption
 	FilterCNAMEs        config.BoolOption
 	PreventBypassing    config.BoolOption
+	DomainHeuristics    config.BoolOption
 }
 
 // NewLayeredProfile returns a new layered profile based on the given local profile.
@@ -108,6 +109,10 @@ func NewLayeredProfile(localProfile *Profile) *LayeredProfile {
 		CfgOptionPreventBypassingKey,
 		cfgOptionPreventBypassing,
 	)
+	new.DomainHeuristics = new.wrapSecurityLevelOption(
+		CfgOptionDomainHeuristicsKey,
+		cfgOptionDomainHeuristics,
+	)
 
 	// TODO: load linked profiles.