diff --git a/mux.go b/mux.go
index eaff897a..b40ab0a5 100644
--- a/mux.go
+++ b/mux.go
@@ -97,6 +97,10 @@ type routeConf struct {
 	// if true, the the http.Request context will not contain the router
 	omitRouterFromContext bool
 
+	// If true, only ampersands (not semicolons) act as separators for
+	// query-parameter pairs.
+	strictQueryParamSep bool
+
 	// Manager for the variables from host and path.
 	regexp routeRegexpGroup
 
@@ -295,6 +299,24 @@ func (r *Router) OmitRouterFromContext(value bool) *Router {
 	return r
 }
 
+// StrictQueryParamSep defines which characters act as separators for
+// query-parameter pairs. The initial value is false, but beware: a future
+// version of this library will adopt true for the initial value.
+//
+// When true, only ampersands act as separators for query parameters.
+// This behavior complies with [the URL Living Standard].
+//
+// When false, both ampersands and semicolons act as separators for
+// query-parameter pairs. This contravenes the URL Living Standard and causes
+// interoperability problems that can lead to [security vulnerabilities].
+//
+// [security vulnerabilities]: https://github.com/gorilla/mux/issues/781
+// [the URL Living Standard]: https://url.spec.whatwg.org/#urlencoded-parsing
+func (r *Router) StrictQueryParamSep(value bool) *Router {
+	r.strictQueryParamSep = value
+	return r
+}
+
 // UseEncodedPath tells the router to match the encoded original path
 // to the routes.
 // For eg. "/path/foo%2Fbar/to" will match the path "/path/{var}/to".
diff --git a/mux_test.go b/mux_test.go
index bac758bc..601070ab 100644
--- a/mux_test.go
+++ b/mux_test.go
@@ -12,10 +12,12 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"maps"
 	"net/http"
 	"net/http/httptest"
 	"net/url"
 	"reflect"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -2067,6 +2069,54 @@ func TestSkipClean(t *testing.T) {
 	}
 }
 
+func TestStrictQueryParamSep(t *testing.T) {
+	cases := []struct {
+		b     bool
+		pairs []string
+		want  map[string]string
+	}{
+		{
+			b:     false,
+			pairs: []string{"foo", "{foo}", "bar", "{bar}", "baz", "{baz}"},
+			want: map[string]string{
+				"foo": "foo",
+				"bar": "bar",
+				"baz": "baz",
+			},
+		}, {
+			b:     true,
+			pairs: []string{"foo", "{foo}", "baz", "{baz}"},
+			want: map[string]string{
+				"foo": "foo;bar=bar",
+				"baz": "baz",
+			},
+		},
+	}
+	for _, tc := range cases {
+		f := func(t *testing.T) {
+			var got map[string]string
+			handle := func(_ http.ResponseWriter, r *http.Request) {
+				got = Vars(r)
+			}
+			r := NewRouter()
+			if r.strictQueryParamSep {
+				t.Error("strickQueryParamSep should be false by default")
+			}
+			r.StrictQueryParamSep(tc.b)
+			r.HandleFunc("/", handle).Queries(tc.pairs...)
+
+			req := httptest.NewRequest("GET", "http://localhost/?foo=foo;bar=bar&baz=baz", nil)
+			res := NewRecorder()
+			r.ServeHTTP(res, req)
+
+			if !maps.Equal(got, tc.want) {
+				t.Errorf("unexpected query params: got %v; want %v", got, tc.want)
+			}
+		}
+		t.Run(strconv.FormatBool(tc.b), f)
+	}
+}
+
 // https://plus.google.com/101022900381697718949/posts/eWy6DjFJ6uW
 func TestSubrouterHeader(t *testing.T) {
 	expected := "func1 response"
diff --git a/regexp.go b/regexp.go
index e0bcff6a..33f775f9 100644
--- a/regexp.go
+++ b/regexp.go
@@ -5,7 +5,6 @@
 package mux
 
 import (
-	"bytes"
 	"fmt"
 	"net/http"
 	"net/url"
@@ -15,8 +14,9 @@ import (
 )
 
 type routeRegexpOptions struct {
-	strictSlash    bool
-	useEncodedPath bool
+	strictSlash         bool
+	useEncodedPath      bool
+	strictQueryParamSep bool
 }
 
 type regexpType int
@@ -245,7 +245,8 @@ func (r *routeRegexp) getURLQuery(req *http.Request) string {
 		return ""
 	}
 	templateKey := strings.SplitN(r.template, "=", 2)[0]
-	val, ok := findFirstQueryKey(req.URL.RawQuery, templateKey)
+	strict := r.options.strictQueryParamSep
+	val, ok := findFirstQueryKey(req.URL.RawQuery, templateKey, strict)
 	if ok {
 		return templateKey + "=" + val
 	}
@@ -254,34 +255,32 @@ func (r *routeRegexp) getURLQuery(req *http.Request) string {
 
 // findFirstQueryKey returns the same result as (*url.URL).Query()[key][0].
 // If key was not found, empty string and false is returned.
-func findFirstQueryKey(rawQuery, key string) (value string, ok bool) {
-	query := []byte(rawQuery)
-	for len(query) > 0 {
-		foundKey := query
-		if i := bytes.IndexAny(foundKey, "&;"); i >= 0 {
-			foundKey, query = foundKey[:i], foundKey[i+1:]
+func findFirstQueryKey(rawQuery, key string, strict bool) (value string, ok bool) {
+	for len(rawQuery) > 0 {
+		foundKey := rawQuery
+		if strict {
+			foundKey, rawQuery, _ = strings.Cut(foundKey, "&")
+		} else if i := strings.IndexAny(foundKey, "&;"); i >= 0 {
+			foundKey, rawQuery = foundKey[:i], foundKey[i+1:]
 		} else {
-			query = query[:0]
+			rawQuery = rawQuery[:0]
 		}
 		if len(foundKey) == 0 {
 			continue
 		}
-		var value []byte
-		if i := bytes.IndexByte(foundKey, '='); i >= 0 {
-			foundKey, value = foundKey[:i], foundKey[i+1:]
-		}
+		foundKey, value, _ := strings.Cut(foundKey, "=")
 		if len(foundKey) < len(key) {
 			// Cannot possibly be key.
 			continue
 		}
-		keyString, err := url.QueryUnescape(string(foundKey))
+		keyString, err := url.QueryUnescape(foundKey)
 		if err != nil {
 			continue
 		}
 		if keyString != key {
 			continue
 		}
-		valueString, err := url.QueryUnescape(string(value))
+		valueString, err := url.QueryUnescape(value)
 		if err != nil {
 			continue
 		}
diff --git a/regexp_test.go b/regexp_test.go
index f7fce81c..9ac96385 100644
--- a/regexp_test.go
+++ b/regexp_test.go
@@ -52,7 +52,7 @@ func Test_findFirstQueryKey(t *testing.T) {
 			all, _ := url.ParseQuery(query)
 			for key, want := range all {
 				t.Run(key, func(t *testing.T) {
-					got, ok := findFirstQueryKey(query, key)
+					got, ok := findFirstQueryKey(query, key, false)
 					if !ok {
 						t.Error("Did not get expected key", key)
 					}
@@ -81,7 +81,7 @@ func Benchmark_findQueryKey(b *testing.B) {
 			b.ResetTimer()
 			for i := 0; i < b.N; i++ {
 				for key := range all {
-					_, _ = findFirstQueryKey(query, key)
+					_, _ = findFirstQueryKey(query, key, false)
 				}
 			}
 		})
diff --git a/route.go b/route.go
index d10401e9..c13e3db6 100644
--- a/route.go
+++ b/route.go
@@ -257,8 +257,9 @@ func (r *Route) addRegexpMatcher(tpl string, typ regexpType) error {
 		}
 	}
 	rr, err := newRouteRegexp(tpl, typ, routeRegexpOptions{
-		strictSlash:    r.strictSlash,
-		useEncodedPath: r.useEncodedPath,
+		strictSlash:         r.strictSlash,
+		useEncodedPath:      r.useEncodedPath,
+		strictQueryParamSep: r.strictQueryParamSep,
 	})
 	if err != nil {
 		return err