restrict private IP access

Author: nkanaev

doc/changelog.md

@@ -4,6 +4,7 @@
 - (new) more auto-refresh options: 12h & 24h (thanks to @aswerkljh for suggestion)
 - (fix) smooth scrolling on iOS (thanks to gatheraled)
 - (etc) cookie security measures (thanks to Tom Fitzhenry)
+- (etc) restrict access to internal IPs for page crawler (thanks to Omar Kurt)
 
 # v2.5 (2025-03-26)
 

src/server/routes.go

@@ -513,6 +513,10 @@ func (s *Server) handlePageCrawl(c *router.Context) {
 		})
 		return
 	}
+	if isInternalFromURL(url) {
+		log.Printf("attempt to access internal IP %s from %s", url, c.Req.RemoteAddr)
+		return
+	}
 
 	body, err := worker.GetBody(url)
 	if err != nil {

src/server/util.go

@@ -0,0 +1,35 @@
+package server
+
+import (
+	"net"
+	"net/url"
+	"strings"
+)
+
+func isInternalFromURL(urlStr string) bool {
+	parsedURL, err := url.Parse(urlStr)
+	if err != nil {
+		return false
+	}
+
+	host := parsedURL.Host
+
+	// Handle "host:port" format
+	if strings.Contains(host, ":") {
+		host, _, err = net.SplitHostPort(host)
+		if err != nil {
+			return false
+		}
+	}
+
+	if host == "localhost" {
+		return true
+	}
+
+	ip := net.ParseIP(host)
+	if ip == nil {
+		return false
+	}
+
+	return ip.IsPrivate() || ip.IsLoopback() || ip.IsLinkLocalUnicast()
+}

src/server/util_test.go

@@ -0,0 +1,31 @@
+package server
+
+import "testing"
+
+func TestIsInternalFromURL(t *testing.T) {
+	tests := []struct {
+		url      string
+		expected bool
+	}{
+		{"http://192.168.1.1:8080", true},
+		{"http://10.0.0.5", true},
+		{"http://172.16.0.1", true},
+		{"http://172.31.255.255", true},
+		{"http://172.32.0.1", false}, // outside private range
+		{"http://127.0.0.1", true},
+		{"http://127.0.0.1:7000", true},
+		{"http://127.0.0.1:7000/secret", true},
+		{"http://169.254.0.5", true},
+		{"http://localhost", true}, // resolves to 127.0.0.1
+		{"http://8.8.8.8", false},
+		{"http://google.com", false}, // resolves to public IPs
+		{"invalid-url", false},       // invalid format
+		{"", false},                  // empty string
+	}
+	for _, test := range tests {
+		result := isInternalFromURL(test.url)
+		if result != test.expected {
+			t.Errorf("isInternalFromURL(%q) = %v; want %v", test.url, result, test.expected)
+		}
+	}
+}