idn: reject conversions that end up as a zero length hostname

Reported-by: RepoRascal on hackerone Closes #18462
2026-04-11 12:01:42 +08:00 · 2025-09-03 09:41:29 +02:00 · 2025-09-03 09:41:29 +02:00 · 967a626af4
commit 967a626af4
parent 8603d5262b
1 changed files with 6 additions and 2 deletions
--- a/lib/idn.c
+++ b/lib/idn.c
@ -323,8 +323,12 @@ CURLcode Curl_idn_decode(const char *input, char **output)
      result = CURLE_OUT_OF_MEMORY;
  }
 #endif
-  if(!result)
-    *output = d;
+  if(!result) {
+    if(!d[0]) /* ended up zero length, not acceptable */
+      result = CURLE_URL_MALFORMAT;
+    else
+      *output = d;
+  }
  return result;
 }