pentest: bind unlock cookie to HMAC per-paste token; serve only safe content types on /raw and can items with nosniff (#34)

cans.go

@@ -258,6 +258,12 @@ func (a *apiServer) handleCanItem(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 	}
-	w.Header().Set("Content-Type", row.ContentType)
+	// #34: same content-type guard as /raw — never serve active content types.
+	ct := row.ContentType
+	if !safeRawContentType(ct) {
+		ct = "text/plain; charset=utf-8"
+	}
+	w.Header().Set("Content-Type", ct)
+	w.Header().Set("X-Content-Type-Options", "nosniff")
 	w.Write([]byte(row.Content))
 }

main.go

@@ -668,11 +668,39 @@ func (a *apiServer) handleRaw(w http.ResponseWriter, r *http.Request) {
 	// #49 decision: raw reads count against the read budget too, with the
 	// same per-viewer 15-minute dedupe window as page views.
 	a.store.registerRead(row, currentViewerID(r))
-	w.Header().Set("Content-Type", row.ContentType)
+	// #34: content_type is attacker-controlled via the create API. Serving it
+	// verbatim let a paste be stored with text/html (or image/svg+xml) and
+	// render as active content on this origin when fetched from /raw —
+	// stored XSS. Only pass through a fixed safe set; anything else is
+	// served as plain text with nosniff.
+	ct := row.ContentType
+	if !safeRawContentType(ct) {
+		ct = "text/plain; charset=utf-8"
+	}
+	w.Header().Set("Content-Type", ct)
+	w.Header().Set("X-Content-Type-Options", "nosniff")
 	a.store.IncrementViews(row.ID)
 	w.Write([]byte(row.Content))
 }
 
+// safeRawContentType reports whether ct is in the fixed set of types that are
+// safe to serve verbatim on /raw (no active-content execution contexts).
+func safeRawContentType(ct string) bool {
+	base := ct
+	if i := strings.IndexByte(ct, ';'); i >= 0 {
+		base = ct[:i]
+	}
+	base = strings.ToLower(strings.TrimSpace(base))
+	switch base {
+	case "text/plain", "text/markdown", "text/x-markdown",
+		"application/json", "application/pdf",
+		"image/png", "image/jpeg", "image/gif", "image/webp",
+		"application/octet-stream":
+		return true
+	}
+	return false
+}
+
 func (a *apiServer) handleCanPage(w http.ResponseWriter, r *http.Request) {
 	id := chi.URLParam(r, "id")
 	can, err := a.store.GetCan(id)

pentest_cookie_test.go

@@ -0,0 +1,42 @@
+package main
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+// #34: the unlock cookie must be bound to the paste it unlocks, not a
+// forgeable static value. A forged 'pw_<id>=1' cookie must not bypass the
+// password check on the paste page.
+func TestForgedUnlockCookieDoesNotBypassPassword(t *testing.T) {
+	globalLimiter = newLimiter()
+	s := testServer(t)
+	h := s.routes()
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest("POST", "/api/pastes", strings.NewReader(`{"content":"SECRETPASTECONTENT","password":"hunter2"}`))
+	h.ServeHTTP(rec, req)
+	if rec.Code != 201 {
+		t.Fatalf("create: got %d", rec.Code)
+	}
+	var created struct {
+		ID string `json:"id"`
+	}
+	json.Unmarshal(rec.Body.Bytes(), &created)
+	id := created.ID
+
+	// request the page with a forged unlock cookie in the old format
+	rec = httptest.NewRecorder()
+	req = httptest.NewRequest("GET", "/"+id, nil)
+	req.AddCookie(&http.Cookie{Name: "pw_" + id, Value: "1"})
+	h.ServeHTTP(rec, req)
+	if rec.Code == 200 && strings.Contains(rec.Body.String(), "SECRETPASTECONTENT") {
+		t.Fatal("forged pw_<id>=1 cookie bypassed password protection")
+	}
+	if rec.Code != 200 {
+		t.Logf("forged-cookie request returned %d (page still locked) — good", rec.Code)
+	}
+}

pentest_helpers_test.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+// test helpers for pentest tests (#34)
+func jsonField(tb testing.TB, body, field string) string {
+	var m map[string]any
+	if err := json.Unmarshal([]byte(body), &m); err != nil {
+		tb.Fatalf("bad json: %v", err)
+	}
+	v, _ := m[field].(string)
+	return v
+}

pentest_rawct_test.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+// #34: attacker-controlled content_type must not let a paste be served as
+// HTML/SVG/XML from /raw (stored XSS). Only a fixed safe set passes through.
+func TestRawRejectsHTMLContentType(t *testing.T) {
+	globalLimiter = newLimiter() // fresh rate-limit buckets
+	s := testServer(t)
+	h := s.routes()
+
+	for _, ct := range []string{
+		"text/html", "TEXT/HTML", "text/html;charset=utf-8", "text/html;x=1",
+		"application/xhtml+xml", "image/svg+xml", "text/html,",
+	} {
+		globalLimiter = newLimiter() // burst 5, loop makes 7 creates
+		body := `{"content":"<script>alert(1)</script>","content_type":"` + ct + `"}`
+		rec := httptest.NewRecorder()
+		req := httptest.NewRequest("POST", "/api/pastes", strings.NewReader(body))
+		h.ServeHTTP(rec, req)
+		if rec.Code != 201 {
+			t.Fatalf("ct %q: create got %d: %s", ct, rec.Code, rec.Body.String())
+		}
+		id := jsonField(t, rec.Body.String(), "id")
+
+		rec = httptest.NewRecorder()
+		req = httptest.NewRequest("GET", "/raw/"+id, nil)
+		h.ServeHTTP(rec, req)
+		if got := rec.Header().Get("Content-Type"); got == ct {
+			t.Errorf("ct %q was served verbatim from /raw (stored XSS vector)", ct)
+		}
+		if got := rec.Header().Get("X-Content-Type-Options"); got != "nosniff" {
+			t.Errorf("ct %q: /raw missing X-Content-Type-Options: nosniff", ct)
+		}
+	}
+}
+
+func TestRawAllowsSafeContentType(t *testing.T) {
+	globalLimiter = newLimiter()
+	s := testServer(t)
+	h := s.routes()
+
+	for _, ct := range []string{"text/plain", "image/png", "application/pdf", "application/octet-stream"} {
+		globalLimiter = newLimiter()
+		body := `{"content":"hi","content_type":"` + ct + `"}`
+		rec := httptest.NewRecorder()
+		req := httptest.NewRequest("POST", "/api/pastes", strings.NewReader(body))
+		h.ServeHTTP(rec, req)
+		if rec.Code != 201 {
+			t.Fatalf("ct %q: create got %d", ct, rec.Code)
+		}
+		id := jsonField(t, rec.Body.String(), "id")
+
+		rec = httptest.NewRecorder()
+		req = httptest.NewRequest("GET", "/raw/"+id, nil)
+		h.ServeHTTP(rec, req)
+		if got := rec.Header().Get("Content-Type"); got != ct {
+			t.Errorf("ct %q: got %q", ct, got)
+		}
+	}
+}

web.go

@@ -1,11 +1,17 @@
 package main
 
 import (
+	"crypto/hmac"
+	cryptorand "crypto/rand"
+	"crypto/sha256"
 	"embed"
+	"encoding/hex"
 	"fmt"
 	"html/template"
 	"io/fs"
+	"log"
 	"net/http"
+	"os"
 	"strconv"
 	"strings"
 	"time"
@@ -58,6 +64,29 @@ func renderPage(w http.ResponseWriter, name string, data any) {
 
 var webUIInstance *webUI
 
+// #34: per-paste unlock tokens. unlockSecret is generated once at startup
+// (also derivable from PALETTE_UNLOCK_SECRET for multi-instance deploys) and
+// used to HMAC paste ids, so a client can only hold a valid pw_<id> cookie by
+// actually submitting the correct password for that paste.
+var unlockSecret = resolveUnlockSecret()
+
+func resolveUnlockSecret() []byte {
+	if v := os.Getenv("PALETTE_UNLOCK_SECRET"); v != "" {
+		return []byte(v)
+	}
+	b := make([]byte, 32)
+	if _, err := cryptorand.Read(b); err != nil {
+		log.Fatal("cannot generate unlock secret: ", err)
+	}
+	return b
+}
+
+func unlockToken(id string) string {
+	mac := hmac.New(sha256.New, unlockSecret)
+	mac.Write([]byte("unlock:" + id))
+	return hex.EncodeToString(mac.Sum(nil))
+}
+
 func (a *apiServer) handleNewPage(w http.ResponseWriter, r *http.Request) {
 	renderPage(w, "new.html", map[string]any{"Page": "new"})
 }
@@ -172,8 +201,12 @@ func (a *apiServer) handlePasteView(w http.ResponseWriter, r *http.Request) {
 			r.ParseForm()
 			pw := r.FormValue("password")
 			if pw != "" && checkPassword(row.PasswordHash.String, pw) {
+				// #34: the unlock cookie must be bound to this specific paste and
+				// unforgable. A static value ("1") let anyone bypass the password
+				// by setting pw_<id>=1 for any paste id. The token is an HMAC of
+				// the paste id under the server's random secret.
 				http.SetCookie(w, &http.Cookie{
-					Name: "pw_" + row.ID, Value: "1", Path: "/",
+					Name: "pw_" + row.ID, Value: unlockToken(row.ID), Path: "/",
 					MaxAge: 3600, HttpOnly: true, SameSite: http.SameSiteLaxMode,
 				})
 				// re-render without lock, or redirect if ?next= was given (#26)
@@ -190,9 +223,9 @@ func (a *apiServer) handlePasteView(w http.ResponseWriter, r *http.Request) {
 			renderPage(w, "unlock.html", map[string]any{"Page": "unlock", "ID": row.ID, "Wrong": true, "CreatedAgo": agoString(row.CreatedAt), "CreatedAtUnix": row.CreatedAt})
 			return
 		}
-		// check cookie
+		// check cookie — must carry the valid per-paste unlock token (#34)
 		c, err := r.Cookie("pw_" + row.ID)
-		if err != nil || c.Value != "1" {
+		if err != nil || c.Value != unlockToken(row.ID) {
 			renderPage(w, "unlock.html", map[string]any{"Page": "unlock", "ID": row.ID, "Wrong": false, "CreatedAgo": agoString(row.CreatedAt), "CreatedAtUnix": row.CreatedAt})
 			return
 		}