doh: allow only http and https in debug mode

Otherwise curl may be told to use for instance pop3 to
communicate with the doh server, which most likely
is not what you want.

Found through fuzzing.

Closes #4406

1 files changed, 3 insertions, 0 deletions

diff --git a/lib/doh.c b/lib/doh.c
index 05a6cc235..196e89d93 100644
--- a/lib/doh.c
+++ b/lib/doh.c
@@ -264,6 +264,9 @@ static CURLcode dohprobe(struct Curl_easy *data,
 #ifndef CURLDEBUG
     /* enforce HTTPS if not debug */
     ERROR_CHECK_SETOPT(CURLOPT_PROTOCOLS, CURLPROTO_HTTPS);
+#else
+    /* in debug mode, also allow http */
+    ERROR_CHECK_SETOPT(CURLOPT_PROTOCOLS, CURLPROTO_HTTP|CURLPROTO_HTTPS);
 #endif
     ERROR_CHECK_SETOPT(CURLOPT_TIMEOUT_MS, (long)timeout_ms);
     if(data->set.verbose)