123 lines
3.0 KiB
Go
123 lines
3.0 KiB
Go
// Copyright (c) 2025-2026 Probo Inc <hello@probo.com>.
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice appear in all copies.
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//
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// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
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// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
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// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
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// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
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// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
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// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
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// PERFORMANCE OF THIS SOFTWARE.
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package saferedirect
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import (
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"context"
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"net/http"
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"net/url"
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"path"
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"strings"
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)
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type (
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AllowedHostFunc func(ctx context.Context, host string) bool
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SafeRedirect struct {
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allowedHost AllowedHostFunc
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}
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)
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func New(allowedHost AllowedHostFunc) *SafeRedirect {
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return &SafeRedirect{allowedHost: allowedHost}
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}
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// StaticHosts returns an AllowedHost function that matches against a fixed
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// list of hosts.
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func StaticHosts(hosts ...string) AllowedHostFunc {
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allowed := make(map[string]bool, len(hosts))
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for _, h := range hosts {
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if h != "" {
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allowed[h] = true
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}
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}
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return func(_ context.Context, host string) bool {
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return allowed[host]
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}
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}
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func (sr *SafeRedirect) Validate(ctx context.Context, redirectURL string) (string, bool) {
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if redirectURL == "" {
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return "", false
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}
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if strings.HasPrefix(redirectURL, "/") {
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safePath, ok := normalizeRelativePath(redirectURL)
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if !ok {
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return "", false
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}
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return safePath, true
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}
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parsedURL, err := url.Parse(redirectURL)
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if err != nil {
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return "", false
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}
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if parsedURL.IsAbs() {
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if parsedURL.Scheme != "http" && parsedURL.Scheme != "https" {
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return "", false
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}
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if sr.allowedHost != nil && !sr.allowedHost(ctx, parsedURL.Host) {
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return "", false
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}
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return redirectURL, true
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}
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return "", false
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}
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func (sr *SafeRedirect) GetSafeRedirectURL(ctx context.Context, redirectURL, fallbackURL string) string {
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if safeURL, isValid := sr.Validate(ctx, redirectURL); isValid {
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return safeURL
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}
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return fallbackURL
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}
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func (sr *SafeRedirect) Redirect(w http.ResponseWriter, r *http.Request, redirectURL, fallbackURL string, statusCode int) {
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safeURL := sr.GetSafeRedirectURL(r.Context(), redirectURL, fallbackURL)
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http.Redirect(w, r, safeURL, statusCode)
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}
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func normalizeRelativePath(redirectURL string) (string, bool) {
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if strings.HasPrefix(redirectURL, "//") {
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return "", false
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}
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if strings.Contains(redirectURL, `\`) || strings.Contains(strings.ToLower(redirectURL), "%5c") {
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return "", false
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}
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cleaned := path.Clean(redirectURL)
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if !strings.HasPrefix(cleaned, "/") {
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return "", false
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}
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if len(cleaned) > 1 && (cleaned[1] == '/' || cleaned[1] == '\\') {
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return "", false
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}
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if strings.Contains(cleaned, `\`) {
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return "", false
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}
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return cleaned, true
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}
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