diff --git a/lib/webrick/httprequest.rb b/lib/webrick/httprequest.rb
index 7a1686b..43e4e8a 100644
--- a/lib/webrick/httprequest.rb
+++ b/lib/webrick/httprequest.rb
@@ -475,6 +475,9 @@ def read_header(socket)
           if (@request_bytes += line.bytesize) > MAX_HEADER_LENGTH
             raise HTTPStatus::RequestEntityTooLarge, 'headers too large'
           end
+          if line.include?("\x00")
+            raise HTTPStatus::BadRequest, 'null byte in header'
+          end
           @raw_header << line
         end
       end
@@ -542,7 +545,7 @@ def read_body(socket, block)
 
     def read_chunk_size(socket)
       line = read_line(socket)
-      if /^([0-9a-fA-F]+)(?:;(\S+))?/ =~ line
+      if /\A([0-9a-fA-F]+)(?:;(\S+(?:=\S+)?))?\r\n\z/ =~ line
         chunk_size = $1.hex
         chunk_ext = $2
         [ chunk_size, chunk_ext ]
diff --git a/test/webrick/test_httprequest.rb b/test/webrick/test_httprequest.rb
index 9033217..c0fb2e9 100644
--- a/test/webrick/test_httprequest.rb
+++ b/test/webrick/test_httprequest.rb
@@ -289,6 +289,40 @@ def test_chunked
     assert_equal(expect, dst.string)
   end
 
+  def test_bad_chunked
+    msg = <<-_end_of_message_
+      POST /path HTTP/1.1\r
+      Transfer-Encoding: chunked\r
+      \r
+      01x1\r
+      \r
+      1
+    _end_of_message_
+    msg.gsub!(/^ {6}/, "")
+    req = WEBrick::HTTPRequest.new(WEBrick::Config::HTTP)
+    req.parse(StringIO.new(msg))
+    assert_raise(WEBrick::HTTPStatus::BadRequest){ req.body }
+
+    # chunked req.body_reader
+    req = WEBrick::HTTPRequest.new(WEBrick::Config::HTTP)
+    req.parse(StringIO.new(msg))
+    dst = StringIO.new
+    assert_raise(WEBrick::HTTPStatus::BadRequest) do
+      IO.copy_stream(req.body_reader, dst)
+    end
+  end
+
+  def test_null_byte_in_header
+    msg = <<-_end_of_message_
+      POST /path HTTP/1.1\r
+      Evil: evil\x00\r
+      \r
+    _end_of_message_
+    msg.gsub!(/^ {6}/, "")
+    req = WEBrick::HTTPRequest.new(WEBrick::Config::HTTP)
+    assert_raise(WEBrick::HTTPStatus::BadRequest){ req.parse(StringIO.new(msg)) }
+  end
+
   def test_forwarded
     msg = <<-_end_of_message_
       GET /foo HTTP/1.1