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CERTVU:605641

HistoryAug 13, 2019 - 12:00 a.m.

HTTP/2 implementations do not robustly handle abnormal traffic and resource exhaustion

2019-08-1300:00:00

www.kb.cert.org

9.1 High

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

NONE

Integrity Impact

HIGH

Availability Impact

HIGH

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

7.8 High

CVSS2

Access Vector

NETWORK

Access Complexity

LOW

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

NONE

Availability Impact

COMPLETE

AV:N/AC:L/Au:N/C:N/I:N/A:C

0.821 High

EPSS

Percentile

98.3%

JSON

Overview

Multiple HTTP/2 implementations are vulnerable to a variety of denial-of-service (DoS) attacks.

Description

The Security Considerations section of RFC7540 discusses some of the considerations needed for HTTP/2 connections as they demand more resources to operate than HTTP/1.1 connections. While it generally covers expected behavior considerations, how to mitigate abnormal behavior is left to the implementer which can leave it open to the following weaknesses.

CVE-2019-9511, also known as Data Dribble
The attacker requests a large amount of data from a specified resource over multiple streams. They manipulate window size and stream priority to force the server to queue the data in 1-byte chunks. Depending on how efficiently this data is queued, this can consume excess CPU, memory, or both, potentially leading to a denial of service.

CVE-2019-9512, also known as Ping Flood
The attacker sends continual pings to an HTTP/2 peer, causing the peer to build an internal queue of responses. Depending on how efficiently this data is queued, this can consume excess CPU, memory, or both, potentially leading to a denial of service.

CVE-2019-9513, also known as Resource Loop
The attacker creates multiple request streams and continually shuffles the priority of the streams in a way that causes substantial churn to the priority tree. This can consume excess CPU, potentially leading to a denial of service.

CVE-2019-9514, also known as Reset Flood
The attacker opens a number of streams and sends an invalid request over each stream that should solicit a stream of RST_STREAM frames from the peer. Depending on how the peer queues the RST_STREAM frames, this can consume excess memory, CPU, or both, potentially leading to a denial of service.

CVE-2019-9515, also known as Settings Flood
The attacker sends a stream of SETTINGS frames to the peer. Since the RFC requires that the peer reply with one acknowledgement per SETTINGS frame, an empty SETTINGS frame is almost equivalent in behavior to a ping. Depending on how efficiently this data is queued, this can consume excess CPU, memory, or both, potentially leading to a denial of service.

CVE-2019-9516, also known as 0-Length Headers Leak
The attacker sends a stream of headers with a 0-length header name and 0-length header value, optionally Huffman encoded into 1-byte or greater headers. Some implementations allocate memory for these headers and keep the allocation alive until the session dies. This can consume excess memory, potentially leading to a denial of service.

CVE-2019-9517, also known as Internal Data Buffering
The attacker opens the HTTP/2 window so the peer can send without constraint; however, they leave the TCP window closed so the peer cannot actually write (many of) the bytes on the wire. The attacker then sends a stream of requests for a large response object. Depending on how the servers queue the responses, this can consume excess memory, CPU, or both, potentially leading to a denial of service.

CVE-2019-9518, also known as Empty Frame Flooding
The attacker sends a stream of frames with an empty payload and without the end-of-stream flag. These frames can be DATA, HEADERS, CONTINUATION and/or PUSH_PROMISE. The peer spends time processing each frame disproportionate to attack bandwidth. This can consume excess CPU, potentially leading to a denial of service.

Impact

These attacks can consume excessive system resources, potentially enough that a single end-system could cause issues on multiple servers that may lead to Distributed DoS (DDoS) attacks.

Solution

Apply an update
Install the latest updates from HTTP/2 implementers.

Vendor Information

Please see this matrix of affected products and vulnerabilities.

605641

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Akamai Technologies, Inc. __ Affected

Notified: August 07, 2019 Updated: August 15, 2019

Statement Date: August 14, 2019

Status

Affected

Vendor Statement

(Updated 8/14/2019) All customer services have been patched.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

Facebook Affected

Updated: August 08, 2019

Status

Affected

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

Go Programming Language Affected

Updated: August 08, 2019

Status

Affected

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

LiteSpeed Technologies __ Affected

Notified: August 15, 2019 Updated: August 17, 2019

Statement Date: August 16, 2019

Status

Affected

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

Fixed in:

LSWS 5.4.1 (CVE-2019-9516)
ADC 2.5.1 (CVE-2019-9516)
OpenLiteSpeed 1.5.5 and 1.4.50 (CVE-2019-9512, CVE-2019-9515, CVE-2019-9516, CVE-2019-9518)

Vendor References

<https://blog.litespeedtech.com/2019/08/15/litespeed-addresses-http-2-dos-advisories/>

Addendum

There are no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us [email](<mailto:[email protected]?Subject=VU%23605641 Feedback>).

Vendor References

Microsoft __ Affected

Notified: August 07, 2019 Updated: August 27, 2019

Status

Affected

Vendor Statement

Microsoft addressed these vulnerabilities in August 2019 updates.

Vendor Information

In addition, CVE-2019-9015 was addressed in February 2019 with the following KB article:
<https://support.microsoft.com/en-us/help/4491420>: Define thresholds on the number of HTTP/2 Settings parameters exchanged over a connection.

Vendor References

Netty Affected

Updated: August 08, 2019

Status

Affected

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

Node.js Affected

Notified: August 07, 2019 Updated: August 08, 2019

Status

Affected

Vendor Statement

We have not received a statement from the vendor.

Vendor Information

We are not aware of further vendor information regarding this vulnerability.

Synology __ Affected

Notified: August 07, 2019 Updated: August 14, 2019

Statement Date: August 14, 2019

Status

Affected

Vendor Statement

Affected.

Vendor References

<https://www.synology.com/security/advisory/Synology_SA_19_33>

View all 236 vendors __View less vendors __

CVSS Metrics

Group	Score	Vector
Base	5	AV:N/AC:L/Au:N/C:N/I:–/A:P
Temporal	3.9	E:POC/RL:OF/RC:C
Environmental	6.3	CDP:LM/TD:H/CR:ND/IR:ND/AR:H

References

Acknowledgements

Thanks to Jonathan Looney of Netflix for reporting CVE-2019-9511, CVE-2019-9512, CVE-2019-9513, CVE-2019-9514, CVE-2019-9515, CVE-2019-9516, and CVE-2019-9517.
Thanks to Piotr Sikora of Google, Envoy Security Team, for reporting CVE-2019-9518.

This document was written by Madison Oliver.