[release-branch.go1.24] 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/+/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>

diff --git a/doc/godebug.md b/doc/godebug.md
index 7f2a98a5395933241527d3cb556a8637fb9c96f1..022687fbb17baa476bae585632ca61a2bd363b78 100644 (file)
--- a/doc/godebug.md
+++ b/doc/godebug.md
@@ -161,6 +161,13 @@ 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 1.24
 
 Go 1.24 added a new `fips140` setting that controls whether the Go

diff --git a/src/internal/godebugs/table.go b/src/internal/godebugs/table.go
index 6a9bf4f8ce0ff839282a2cca839c2441c8c34320..103cf0184892eb9a013c8279eae3609bc566c10e 100644 (file)
--- a/src/internal/godebugs/table.go
+++ b/src/internal/godebugs/table.go
@@ -61,6 +61,7 @@ var All = []Info{
        {Name: "tlsmlkem", Package: "crypto/tls", Changed: 24, Old: "0", Opaque: true},
        {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: "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 1d9c1cd99fa0305240931de14cc326eeb1ae0116..97ed30749eae4292796f925567f0932f387c1bbe 100644 (file)
--- a/src/net/url/url.go
+++ b/src/net/url/url.go
@@ -13,6 +13,7 @@ package url
 import (
        "errors"
        "fmt"
+       "internal/godebug"
        "maps"
        "net/netip"
        "path"
@@ -989,7 +990,30 @@ 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 079e801ab57d123d9292ee74f05c815b654e6191..ab54f0687f548bcfb7e416ae23562d9518bd63df 100644 (file)
--- a/src/runtime/metrics/doc.go
+++ b/src/runtime/metrics/doc.go
@@ -354,6 +354,11 @@ 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/winreadlinkvolume:events
                The number of non-default behaviors executed by the os package
                due to a non-default GODEBUG=winreadlinkvolume=... setting.