From a94973805df96269bf3f3bf0a20ccb9887313316 Mon Sep 17 00:00:00 2001
From: Daniel Stenberg <daniel@haxx.se>
Date: Wed, 9 Oct 2024 10:04:35 +0200
Subject: [PATCH] hsts: improve subdomain handling

- on load, only replace existing HSTS entries if there is a full host
  match

- on matching, prefer a full host match and secondary the longest tail
  subdomain match

Closes #15210

CVE: CVE-2024-9681
Upstream-Status: Backport [https://github.com/curl/curl/commit/a94973805df96269bf3f3bf0a20ccb9887313316]
Signed-off-by: Peter Marko <peter.marko@siemens.com>
---
 lib/hsts.c          | 14 ++++++++++----
 tests/data/test1660 |  2 +-
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/lib/hsts.c b/lib/hsts.c
index d5e883f51ef0f7..12052ce53c1c5a 100644
--- a/lib/hsts.c
+++ b/lib/hsts.c
@@ -254,12 +254,14 @@ CURLcode Curl_hsts_parse(struct hsts *h, const char *hostname,
 struct stsentry *Curl_hsts(struct hsts *h, const char *hostname,
                            bool subdomain)
 {
+  struct stsentry *bestsub = NULL;
   if(h) {
     char buffer[MAX_HSTS_HOSTLEN + 1];
     time_t now = time(NULL);
     size_t hlen = strlen(hostname);
     struct Curl_llist_element *e;
     struct Curl_llist_element *n;
+    size_t blen = 0;
 
     if((hlen > MAX_HSTS_HOSTLEN) || !hlen)
       return NULL;
@@ -284,15 +286,19 @@ struct stsentry *Curl_hsts(struct hsts *h, const char *hostname,
         if(ntail < hlen) {
           size_t offs = hlen - ntail;
           if((hostname[offs-1] == '.') &&
-             strncasecompare(&hostname[offs], sts->host, ntail))
-            return sts;
+             strncasecompare(&hostname[offs], sts->host, ntail) &&
+             (ntail > blen)) {
+            /* save the tail match with the longest tail */
+            bestsub = sts;
+            blen = ntail;
+          }
         }
       }
       if(strcasecompare(hostname, sts->host))
         return sts;
     }
   }
-  return NULL; /* no match */
+  return bestsub;
 }
 
 /*
@@ -444,7 +450,7 @@ static CURLcode hsts_add(struct hsts *h, char *line)
     e = Curl_hsts(h, p, subdomain);
     if(!e)
       result = hsts_create(h, p, subdomain, expires);
-    else {
+    else if(strcasecompare(p, e->host)) {
       /* the same host name, use the largest expire time */
       if(expires > e->expires)
         e->expires = expires;
diff --git a/tests/data/test1660 b/tests/data/test1660
index f86126d19cf269..4b6f9615c9d517 100644
--- a/tests/data/test1660
+++ b/tests/data/test1660
@@ -52,7 +52,7 @@ this.example [this.example]: 1548400797
 Input 12: error 43
 Input 13: error 43
 Input 14: error 43
-3.example.com [example.com]: 1569905261 includeSubDomains
+3.example.com [3.example.com]: 1569905261 includeSubDomains
 3.example.com [example.com]: 1569905261 includeSubDomains
 foo.example.com [example.com]: 1569905261 includeSubDomains
 'foo.xample.com' is not HSTS
