From bf06767a9ac737387eee77c7eedd67c65e853ac2 Mon Sep 17 00:00:00 2001
From: Damien Neil <dneil@google.com>
Date: Mon, 3 Nov 2025 14:28:47 -0800
Subject: [PATCH] [release-branch.go1.24] net/url: add urlmaxqueryparams
 GODEBUG to limit the number of query parameters

net/url does not currently limit the number of query parameters parsed by
url.ParseQuery or URL.Query.

When parsing a application/x-www-form-urlencoded form,
net/http.Request.ParseForm will parse up to 10 MB of query parameters.
An input consisting of a large number of small, unique parameters can
cause excessive memory consumption.

We now limit the number of query parameters parsed to 10000 by default.
The limit can be adjusted by setting GODEBUG=urlmaxqueryparams=<n>.
Setting urlmaxqueryparams to 0 disables the limit.

Thanks to jub0bs for reporting this issue.

Fixes #77101
Fixes CVE-2025-61726

CVE: CVE-2025-61726
Upstream-Status: Backport [https://github.com/golang/go/commit/85c794ddce26]

Change-Id: Iee3374c7ee2d8586dbf158536d3ade424203ff66
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/3020
Reviewed-by: Nicholas Husin <husin@google.com>
Reviewed-by: Neal Patel <nealpatel@google.com>
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/3326
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/736702
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
TryBot-Bypass: Michael Pratt <mpratt@google.com>
(cherry picked from commit 85c794ddce26a092b0ea68d0fca79028b5069d5a)
Signed-off-by: Deepak Rathore <deeratho@cisco.com>
Signed-off-by: Eduardo Ferreira <eduardo.barbosa@toradex.com>
---
 doc/godebug.md                 |  7 +++++
 src/internal/godebugs/table.go |  1 +
 src/net/url/url.go             | 24 +++++++++++++++++
 src/net/url/url_test.go        | 48 ++++++++++++++++++++++++++++++++++
 src/runtime/metrics/doc.go     |  5 ++++
 5 files changed, 85 insertions(+)

diff --git a/doc/godebug.md b/doc/godebug.md
index ae4f057..635597e 100644
--- a/doc/godebug.md
+++ b/doc/godebug.md
@@ -126,6 +126,13 @@ for example,
 see the [runtime documentation](/pkg/runtime#hdr-Environment_Variables)
 and the [go command documentation](/cmd/go#hdr-Build_and_test_caching).

+Go 1.26 added a new `urlmaxqueryparams` setting that controls the maximum number
+of query parameters that net/url will accept when parsing a URL-encoded query string.
+If the number of parameters exceeds the number set in `urlmaxqueryparams`,
+parsing will fail early. The default value is `urlmaxqueryparams=10000`.
+Setting `urlmaxqueryparams=0`bles the limit. To avoid denial of service attacks,
+this setting and default was backported to Go 1.25.4 and Go 1.24.10.
+
 Go 1.23.11 disabled build information stamping when multiple VCS are detected due
 to concerns around VCS injection attacks. This behavior can be renabled with the
 setting `allowmultiplevcs=1`.
diff --git a/src/internal/godebugs/table.go b/src/internal/godebugs/table.go
index 33dcd81..7178df6 100644
--- a/src/internal/godebugs/table.go
+++ b/src/internal/godebugs/table.go
@@ -51,6 +51,7 @@ var All = []Info{
	{Name: "tlsmaxrsasize", Package: "crypto/tls"},
	{Name: "tlsrsakex", Package: "crypto/tls", Changed: 22, Old: "1"},
	{Name: "tlsunsafeekm", Package: "crypto/tls", Changed: 22, Old: "1"},
+	{Name: "urlmaxqueryparams", Package: "net/url", Changed: 24, Old: "0"},
	{Name: "x509sha1", Package: "crypto/x509"},
	{Name: "x509usefallbackroots", Package: "crypto/x509"},
	{Name: "x509usepolicies", Package: "crypto/x509"},
diff --git a/src/net/url/url.go b/src/net/url/url.go
index d2ae032..cdca468 100644
--- a/src/net/url/url.go
+++ b/src/net/url/url.go
@@ -13,6 +13,7 @@ package url
 import (
	"errors"
	"fmt"
+	"internal/godebug"
	"net/netip"
	"path"
	"sort"
@@ -958,7 +959,30 @@ func ParseQuery(query string) (Values, error) {
	return m, err
 }

+var urlmaxqueryparams = godebug.New("urlmaxqueryparams")
+
+const defaultMaxParams = 10000
+
+func urlParamsWithinMax(params int) bool {
+	withinDefaultMax := params <= defaultMaxParams
+	if urlmaxqueryparams.Value() == "" {
+		return withinDefaultMax
+	}
+	customMax, err := strconv.Atoi(urlmaxqueryparams.Value())
+	if err != nil {
+		return withinDefaultMax
+	}
+	withinCustomMax := customMax == 0 || params < customMax
+	if withinDefaultMax != withinCustomMax {
+		urlmaxqueryparams.IncNonDefault()
+	}
+	return withinCustomMax
+}
+
 func parseQuery(m Values, query string) (err error) {
+	if !urlParamsWithinMax(strings.Count(query, "&") + 1) {
+		return errors.New("number of URL query parameters exceeded limit")
+	}
	for query != "" {
		var key string
		key, query, _ = strings.Cut(query, "&")
diff --git a/src/net/url/url_test.go b/src/net/url/url_test.go
index fef236e..b2f8bd9 100644
--- a/src/net/url/url_test.go
+++ b/src/net/url/url_test.go
@@ -1488,6 +1488,54 @@ func TestParseQuery(t *testing.T) {
	}
 }

+func TestParseQueryLimits(t *testing.T) {
+	for _, test := range []struct {
+		params  int
+		godebug string
+		wantErr bool
+	}{{
+		params:  10,
+		wantErr: false,
+	}, {
+		params:  defaultMaxParams,
+		wantErr: false,
+	}, {
+		params:  defaultMaxParams + 1,
+		wantErr: true,
+	}, {
+		params:  10,
+		godebug: "urlmaxqueryparams=9",
+		wantErr: true,
+	}, {
+		params:  defaultMaxParams + 1,
+		godebug: "urlmaxqueryparams=0",
+		wantErr: false,
+	}} {
+		t.Setenv("GODEBUG", test.godebug)
+		want := Values{}
+		var b strings.Builder
+		for i := range test.params {
+			if i > 0 {
+				b.WriteString("&")
+			}
+			p := fmt.Sprintf("p%v", i)
+			b.WriteString(p)
+			want[p] = []string{""}
+		}
+		query := b.String()
+		got, err := ParseQuery(query)
+		if gotErr, wantErr := err != nil, test.wantErr; gotErr != wantErr {
+			t.Errorf("GODEBUG=%v ParseQuery(%v params) = %v, want error: %v", test.godebug, test.params, err, wantErr)
+		}
+		if err != nil {
+			continue
+		}
+		if got, want := len(got), test.params; got != want {
+			t.Errorf("GODEBUG=%v ParseQuery(%v params): got %v params, want %v", test.godebug, test.params, got, want)
+		}
+	}
+}
+
 type RequestURITest struct {
	url *URL
	out string
diff --git a/src/runtime/metrics/doc.go b/src/runtime/metrics/doc.go
index 517ec0e..88d6d8c 100644
--- a/src/runtime/metrics/doc.go
+++ b/src/runtime/metrics/doc.go
@@ -328,6 +328,11 @@ Below is the full list of supported metrics, ordered lexicographically.
		The number of non-default behaviors executed by the crypto/tls
		package due to a non-default GODEBUG=tlsunsafeekm=... setting.

+	/godebug/non-default-behavior/urlmaxqueryparams:events
+		The number of non-default behaviors executed by the net/url
+		package due to a non-default GODEBUG=urlmaxqueryparams=...
+		setting.
+
	/godebug/non-default-behavior/x509sha1:events
		The number of non-default behaviors executed by the crypto/x509
		package due to a non-default GODEBUG=x509sha1=... setting.
--
2.34.1
