diff --git a/app/v1/self.go b/app/v1/self.go
index fc85a2b..e517e49 100644
--- a/app/v1/self.go
+++ b/app/v1/self.go
@@ -58,6 +58,12 @@ type userSettingsData struct {
 func UsersSelfSettingsPOST(md common.MethodData) common.CodeMessager {
 	var d userSettingsData
 	md.RequestData.Unmarshal(&d)
+
+	// input sanitisation
+	d.UsernameAKA = common.SanitiseString(d.UsernameAKA)
+	d.CustomBadge.Name = common.SanitiseString(d.CustomBadge.Name)
+	d.FavouriteMode = intPtrIn(0, d.FavouriteMode, 3)
+
 	q := new(common.UpdateQuery).
 		Add("s.username_aka", d.UsernameAKA).
 		Add("s.favourite_mode", d.FavouriteMode).
@@ -114,3 +120,16 @@ WHERE u.id = ?`, md.ID()).Scan(
 	}
 	return r
 }
+
+func intPtrIn(x int, y *int, z int) *int {
+	if y == nil {
+		return nil
+	}
+	if *y > z {
+		return nil
+	}
+	if *y < x {
+		return nil
+	}
+	return y
+}
diff --git a/app/v1/user.go b/app/v1/user.go
index 7d2ba44..5709fd7 100644
--- a/app/v1/user.go
+++ b/app/v1/user.go
@@ -345,7 +345,8 @@ func UserSelfUserpagePOST(md common.MethodData) common.CodeMessager {
 	if d.Data == nil {
 		return ErrMissingField("data")
 	}
-	_, err := md.DB.Exec("UPDATE users_stats SET userpage_content = ? WHERE id = ? LIMIT 1", *d.Data, md.ID())
+	cont := common.SanitiseString(*d.Data)
+	_, err := md.DB.Exec("UPDATE users_stats SET userpage_content = ? WHERE id = ? LIMIT 1", cont, md.ID())
 	if err != nil {
 		md.Err(err)
 	}
diff --git a/common/sanitisation.go b/common/sanitisation.go
new file mode 100644
index 0000000..1b4d61e
--- /dev/null
+++ b/common/sanitisation.go
@@ -0,0 +1,16 @@
+package common
+
+import (
+	"unicode"
+)
+
+// SanitiseString removes all control codes from a string.
+func SanitiseString(s string) string {
+	n := make([]rune, 0, len(s))
+	for _, c := range s {
+		if !unicode.Is(unicode.Other, c) {
+			n = append(n, c)
+		}
+	}
+	return string(n)
+}
diff --git a/common/sanitisation_test.go b/common/sanitisation_test.go
new file mode 100644
index 0000000..953eb09
--- /dev/null
+++ b/common/sanitisation_test.go
@@ -0,0 +1,41 @@
+package common
+
+import "testing"
+
+const pen = "I trattori di palmizio 나는 펜이있다. 私はリンゴを持っています。" +
+	"啊! 苹果笔。 у меня есть ручка, Tôi có dứa. අන්නාසි පෑන"
+
+func TestSanitiseString(t *testing.T) {
+	tests := []struct {
+		name string
+		arg  string
+		want string
+	}{
+		{
+			"Normal",
+			pen,
+			pen,
+		},
+		{
+			"Arabic (rtl)",
+			"أناناس",
+			"أناناس",
+		},
+		{
+			"Null",
+			"A\x00B",
+			"AB",
+		},
+	}
+	for _, tt := range tests {
+		if got := SanitiseString(tt.arg); got != tt.want {
+			t.Errorf("%q. SanitiseString() = %v, want %v", tt.name, got, tt.want)
+		}
+	}
+}
+
+func BenchmarkSanitiseString(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		SanitiseString(pen)
+	}
+}