[release-branch.go1.25] net/url: add urlmaxqueryparams GODEBUG to limit the number...

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

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/+/3325
Reviewed-by: Roland Shoemaker <bracewell@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/736723
Reviewed-by: Junyang Shao <shaojunyang@google.com>
TryBot-Bypass: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>

diff --git a/doc/godebug.md b/doc/godebug.md
index c12ce5311d90d11bed1794f7b3f696fa6254270e..a6e64d16efe45de4e5d11e66486a425ada3d378b 100644 (file)
--- a/doc/godebug.md
+++ b/doc/godebug.md
@@ -163,6 +163,13 @@ will fail early. The default value is `httpcookiemaxnum=3000`. Setting
 number of cookies. To avoid denial of service attacks, this setting and default
 was backported to Go 1.25.2 and Go 1.24.8.
 
+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 1.25
 
 Go 1.25 added a new `decoratemappings` setting that controls whether the Go

diff --git a/src/internal/godebugs/table.go b/src/internal/godebugs/table.go
index 852305e8553aab4069d58efc250ad743604e15f9..1d4a329fef3d55bbef363117edbd5af717ba00e2 100644 (file)
--- a/src/internal/godebugs/table.go
+++ b/src/internal/godebugs/table.go
@@ -67,6 +67,7 @@ var All = []Info{
        {Name: "tlssha1", Package: "crypto/tls", Changed: 25, Old: "1"},
        {Name: "tlsunsafeekm", Package: "crypto/tls", Changed: 22, Old: "1"},
        {Name: "updatemaxprocs", Package: "runtime", Changed: 25, Old: "0"},
+       {Name: "urlmaxqueryparams", Package: "net/url", Changed: 24, Old: "0"},
        {Name: "winreadlinkvolume", Package: "os", Changed: 23, Old: "0"},
        {Name: "winsymlink", Package: "os", Changed: 23, Old: "0"},
        {Name: "x509keypairleaf", Package: "crypto/tls", Changed: 23, Old: "0"},

diff --git a/src/net/url/url.go b/src/net/url/url.go
index 1c50e069613a812adffbe9cc97f20bdecf3d9cf8..a0974b1ed1be074ce713142140a7dd0f03abd2eb 100644 (file)
--- a/src/net/url/url.go
+++ b/src/net/url/url.go
@@ -15,6 +15,7 @@ package url
 import (
        "errors"
        "fmt"
+       "internal/godebug"
        "maps"
        "net/netip"
        "path"
@@ -992,7 +993,30 @@ 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 6084facacc0519b0caebd232b67d0f8edbf43898..944124d20edbf76ed8744cd766e404838590abf0 100644 (file)
--- a/src/net/url/url_test.go
+++ b/src/net/url/url_test.go
@@ -1496,6 +1496,54 @@ 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 251ee22fa1a51b9c95981873eec655042f578293..bd90b5f894c8b3856c85f6e7b1aa1665b0153629 100644 (file)
--- a/src/runtime/metrics/doc.go
+++ b/src/runtime/metrics/doc.go
@@ -372,6 +372,11 @@ Below is the full list of supported metrics, ordered lexicographically.
                The number of non-default behaviors executed by the runtime
                package due to a non-default GODEBUG=updatemaxprocs=... 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/winreadlinkvolume:events
                The number of non-default behaviors executed by the os package
                due to a non-default GODEBUG=winreadlinkvolume=... setting.