From 4998ad745b67edeadefe541c94ed029b53933d3b Mon Sep 17 00:00:00 2001
From: Mark Thomas <markt@apache.org>
Date: Tue, 22 Aug 2023 11:31:23 -0700
Subject: [PATCH] Avoid protocol relative redirects

---
 .../apache/catalina/authenticator/FormAuthenticator.java    | 6 ++++++
 webapps/docs/changelog.xml                                  | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/java/org/apache/catalina/authenticator/FormAuthenticator.java b/java/org/apache/catalina/authenticator/FormAuthenticator.java
index a57db51776b6..d54cc62182e5 100644
--- a/java/org/apache/catalina/authenticator/FormAuthenticator.java
+++ b/java/org/apache/catalina/authenticator/FormAuthenticator.java
@@ -747,6 +747,12 @@ protected String savedRequestURL(Session session) {
             sb.append('?');
             sb.append(saved.getQueryString());
         }
+
+        // Avoid protocol relative redirects
+        while (sb.length() > 1 && sb.charAt(1) == '/') {
+            sb.deleteCharAt(0);
+        }
+
         return sb.toString();
     }
 }
diff --git a/webapps/docs/changelog.xml b/webapps/docs/changelog.xml
index bacf432793ca..9eadbe2b8c72 100644
--- a/webapps/docs/changelog.xml
+++ b/webapps/docs/changelog.xml
@@ -117,6 +117,9 @@
         Update code comments and Tomcat output to use MiB for 1024 * 1024 bytes
         and KiB for 1024 bytes rather than MB and kB. (martk)
       </fix>
+      <fix>
+        Avoid protocol relative redirects in FORM authentication. (markt)
+      </fix>
     </changelog>
   </subsection>
   <subsection name="Web applications">