Backported of:

From 7035676c3daa4f1c3766095561f12e7a0e82c736 Mon Sep 17 00:00:00 2001
From: Daniel Stenberg <daniel@haxx.se>
Date: Mon, 16 May 2022 16:28:13 +0200
Subject: [PATCH] content_encoding: return error on too many compression steps

The max allowed steps is arbitrarily set to 5.
diff --git a/lib/content_encoding.c b/lib/content_encoding.c
index 82fcc2b..a89bb3e 100644
--- a/lib/content_encoding.c
+++ b/lib/content_encoding.c
@@ -1027,6 +1027,9 @@ static const struct content_encoding *find_encoding(const char *name,
   return NULL;
 }
 
+/* allow no more than 5 "chained" compression steps */
+#define MAX_ENCODE_STACK 5
+
 /* Set-up the unencoding stack from the Content-Encoding header value.
  * See RFC 7231 section 3.1.2.2. */
 CURLcode Curl_build_unencoding_stack(struct connectdata *conn,
@@ -1034,6 +1037,7 @@ CURLcode Curl_build_unencoding_stack(struct connectdata *conn,
 {
   struct Curl_easy *data = conn->data;
   struct SingleRequest *k = &data->req;
+  int counter = 0;
 
   do {
     const char *name;
@@ -1068,6 +1072,11 @@ CURLcode Curl_build_unencoding_stack(struct connectdata *conn,
       if(!encoding)
         encoding = &error_encoding;  /* Defer error at stack use. */
 
+      if(++counter >= MAX_ENCODE_STACK) {
+        failf(data, "Reject response due to %u content encodings",
+              counter);
+        return CURLE_BAD_CONTENT_ENCODING;
+      }
       /* Stack the unencoding stage. */
       writer = new_unencoding_writer(conn, encoding, k->writer_stack);
       if(!writer)