httpbis M. Chen Internet-Draft Li. Su Intended status: Informational China Mobile Expires: December 17, 2021 June 15, 2021 http2 window size use case draft-chen-httpbis-window-size-use-case-01 Abstract This document presents an use case which actually happening in our network, when window_size_increment in the window update frame less than 128 bytes and the increased window size also less than 128 bytes, then network connection will come to an error. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on December 17, 2021. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Chen & Su Expires December 17, 2021 [Page 1] Internet-Draft http2 window size use case June 2021 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Use Case . . . . . . . . . . . . . . . . . . . . . . . . . . 2 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 6. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 4 7. Informative References . . . . . . . . . . . . . . . . . . . 4 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction The following content is from RFC 7540[RFC7540] When an HTTP/2 connection is first established, new streams are created with an initial flow-control window size of 65,535 octets. The connection flow-control window is also 65,535 octets. Both endpoints can adjust the initial window size for new streams by including a value for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame that forms part of the connection preface. The connection flow-control window can only be changed using WINDOW_UPDATE frames. SETTINGS_INITIAL_WINDOW_SIZE (0x4): Indicates the sender's initial window size (in octets) for stream-level flow control. The initial value is 2^16-1 (65,535) octets. Window Size Increment defined in the Window_update is 31, the legal range for the increment to the flow-control window is 1 to 2^31-1 (2,147,483,647) octets. RFC 7540 just Specifies the maximum value of Window and the Window Size Increment, But there is no obvious rule about minimum values. 2. Terminology The readers should be familiar with the terms defined in. In addition, this document makes use of the following terms: Window_update: The WINDOW_UPDATE frame (type=0x8) is used to implement flow control; 3. Use Case This section describes use case which happens between two different manufacturers. They both use HTTP2.0 protocol to transmit messages. We found this phenomenon, one issues a regular registration request, Chen & Su Expires December 17, 2021 [Page 2] Internet-Draft http2 window size use case June 2021 the other one receives the request, but judged to be attack behaviour. +---------+ +----------+ | Sender | |Receiver | | | | | +----+----+ +-----+----+ | Reqistration request | +-----------------------------------> | | | | +-----------------------------------> | Http2 Window_update | | (condition1:window size | | increment) | | |window+=window size increment | |condition2: window | | | |condition1<128bytes | connection break |& condition2<128bytes | +-------------------------+ |=attack behaviour | | | Registration Failed | +<----------------------------------+ + + Figure 1: A normal request is considered an attack Why determine abnormal attack behavior, the analysis is as follows: The default initial window size defined by the protocol is 64K. After the data in the receiving window is removed, part of the window occupied by the original data is released. If there is a large backlog of data in the original receiving window that has not been removed, resulting in a small remaining window, the window added after the normal removal of data will not be too small. If there is little backlog of data in the original receiving window, the window that needs to be added after the data is removed will be small, but the overall available window after the adjustment will be larger. In neither case will the window be too small, So the connection considered to be an attack. So when need to solve this problem, two approaches can be discussed, specifying a minimum value for window and window size increment, or increasing more detailed flow control strategies. Chen & Su Expires December 17, 2021 [Page 3] Internet-Draft http2 window size use case June 2021 4. Security Considerations Failure to set a minimum will result in frequent window_update if only process a small amount of data at a time, it is likely to occur Denial of service attacks, it would be fatal if it happened in an Internet of Things scenario. In draft-ietf-httpbis-http2bis, there are also Denial-of-Service consideration in section 10.5, includes the misuse of some parameters and priorities. 5. IANA Considerations This document does not require any action from IANA. 6. Acknowledgement TBD 7. Informative References [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext Transfer Protocol Version 2 (HTTP/2)", RFC 7540, DOI 10.17487/RFC7540, May 2015, . Authors' Addresses Meiling Chen China Mobile 32, Xuanwumen West BeiJing, BeiJing 100053 China Email: chenmeiling@chinamobile.com Chen & Su Expires December 17, 2021 [Page 4] Internet-Draft http2 window size use case June 2021 Li Su China Mobile 32, Xuanwumen West BeiJing 100053 China Email: suli@chinamobile.com Chen & Su Expires December 17, 2021 [Page 5]