[SECURITY] Allowlisting and changed salts for safelink and safelink_callback (CVE-2026-13602)

---------

Co-authored-by: Raphael Michel <michel@pretix.eu>

src/pretix/base/templatetags/rich_text.py

@@ -42,8 +42,6 @@ from bleach import DEFAULT_CALLBACKS, html5lib_shim
 from bleach.linkifier import build_email_re
 from django import template
 from django.conf import settings
-from django.core import signing
-from django.urls import reverse
 from django.utils.functional import SimpleLazyObject
 from django.utils.html import escape
 from django.utils.http import url_has_allowed_host_and_scheme
@@ -54,6 +52,7 @@ from markdown.postprocessors import Postprocessor
 from markdown.treeprocessors import UnescapeTreeprocessor
 from tlds import tld_set
 
+from pretix.base.views.redirect import safelink
 from pretix.helpers.format import SafeFormatter, format_map
 
 register = template.Library()
@@ -158,8 +157,7 @@ def safelink_callback(attrs, new=False):
     """
     url = html.unescape(attrs.get((None, 'href'), '/'))
     if not url_has_allowed_host_and_scheme(url, allowed_hosts=None) and not url.startswith('mailto:') and not url.startswith('tel:'):
-        signer = signing.Signer(salt='safe-redirect')
-        attrs[None, 'href'] = reverse('redirect') + '?url=' + urllib.parse.quote(signer.sign(url))
+        attrs[None, 'href'] = safelink(url)
         attrs[None, 'target'] = '_blank'
         attrs[None, 'rel'] = 'noopener'
     return attrs

src/pretix/base/views/redirect.py

@@ -19,6 +19,7 @@
 # You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
 # <https://www.gnu.org/licenses/>.
 #
+import logging
 import urllib.parse
 
 from django.core import signing
@@ -26,6 +27,8 @@ from django.http import HttpResponseBadRequest, HttpResponseRedirect
 from django.shortcuts import render
 from django.urls import reverse
 
+logger = logging.getLogger(__name__)
+
 
 def _is_samesite_referer(request):
     referer = request.headers.get('referer')
@@ -42,11 +45,14 @@ def _is_samesite_referer(request):
 
 
 def redir_view(request):
-    signer = signing.Signer(salt='safe-redirect')
     try:
-        url = signer.unsign(request.GET.get('url', ''))
+        url = signing.Signer(salt='safelink-url').unsign(request.GET.get('url', ''))
     except signing.BadSignature:
-        return HttpResponseBadRequest('Invalid parameter')
+        try:
+            # Backwards-compatibility for a change in 2026-06, remove after a while
+            url = signing.Signer(salt='safe-redirect').unsign(request.GET.get('url', ''))
+        except signing.BadSignature:
+            return HttpResponseBadRequest('Invalid parameter')
 
     if not _is_samesite_referer(request):
         u = urllib.parse.urlparse(url)
@@ -61,5 +67,9 @@ def redir_view(request):
 
 
 def safelink(url):
-    signer = signing.Signer(salt='safe-redirect')
+    url = str(url)
+    if not (url.startswith('https://') or url.startswith('http://') or url.startswith("/")):
+        logger.warning('Invalid URL passed to safelink: %r', url)
+        return '#invalid-url'
+    signer = signing.Signer(salt='safelink-url')
     return reverse('redirect') + '?url=' + urllib.parse.quote(signer.sign(url))

src/tests/base/test_rich_text.py

@@ -119,7 +119,7 @@ def test_linkify_abs(link):
     assert markdown_compile_email(input) == f"<p>{output}</p>"
 
 
-signer = signing.Signer(salt='safe-redirect')
+signer = signing.Signer(salt='safelink-url')
 
 
 @pytest.mark.parametrize(