net/http: strip sensitive proxy headers from redirect requests

Similarly to Authentication entries, Proxy-Authentication entries should be stripped to ensure sensitive information is not leaked on redirects outside of the original domain.

https://fetch.spec.whatwg.org/#authentication-entries

Thanks to Takeshi Kaneko (GMO Cybersecurity by Ierae, Inc.) for reporting this issue.

For #73816
Fixes CVE-2025-4673

Change-Id: Ied7b641f6531f1d340ccba3c636d3c30dd5547d9
Reviewed-on: https://go-review.googlesource.com/c/go/+/679257
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>

Author: thatnealpatel

src/net/http/client.go

@@ -806,7 +806,8 @@ func (c *Client) makeHeadersCopier(ireq *Request) func(req *Request, stripSensit
 		for k, vv := range ireqhdr {
 			sensitive := false
 			switch CanonicalHeaderKey(k) {
-			case "Authorization", "Www-Authenticate", "Cookie", "Cookie2":
+			case "Authorization", "Www-Authenticate", "Cookie", "Cookie2",
+				"Proxy-Authorization", "Proxy-Authenticate":
 				sensitive = true
 			}
 			if !(sensitive && stripSensitiveHeaders) {

src/net/http/client_test.go

@@ -1550,6 +1550,8 @@ func testClientStripHeadersOnRepeatedRedirect(t *testing.T, mode testMode) {
 		if r.Host+r.URL.Path != "a.example.com/" {
 			if h := r.Header.Get("Authorization"); h != "" {
 				t.Errorf("on request to %v%v, Authorization=%q, want no header", r.Host, r.URL.Path, h)
+			} else if h := r.Header.Get("Proxy-Authorization"); h != "" {
+				t.Errorf("on request to %v%v, Proxy-Authorization=%q, want no header", r.Host, r.URL.Path, h)
 			}
 		}
 		// Follow a chain of redirects from a to b and back to a.
@@ -1578,6 +1580,7 @@ func testClientStripHeadersOnRepeatedRedirect(t *testing.T, mode testMode) {
 	req, _ := NewRequest("GET", proto+"://a.example.com/", nil)
 	req.Header.Add("Cookie", "foo=bar")
 	req.Header.Add("Authorization", "secretpassword")
+	req.Header.Add("Proxy-Authorization", "secretpassword")
 	res, err := c.Do(req)
 	if err != nil {
 		t.Fatal(err)