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HTTP/2 Implementation Vulnerabilities Expose Servers to DoS Attacks

Researchers at Netflix and Google have discovered a total of eight denial-of-service (DoS) vulnerabilities affecting various HTTP/2 implementations, including from major tech companies such as Amazon, Apple, Facebook and Microsoft.

Researchers at Netflix and Google have discovered a total of eight denial-of-service (DoS) vulnerabilities affecting various HTTP/2 implementations, including from major tech companies such as Amazon, Apple, Facebook and Microsoft.

According to Netflix, which coordinated the disclosure of the vulnerabilities with Google and CERT/CC, the flaws are related to resource exhaustion and they can be exploited to launch DoS attacks against servers that support HTTP/2.

HTTP/2, the second major revision of the HTTP internet protocol, is designed to make applications faster, simpler and more robust.

None of the security holes found by Netflix and Google researchers allow an attacker to obtain or modify protected information.

“Rather, they allow a small number of low bandwidth malicious sessions to prevent connection participants from doing additional work. These attacks are likely to exhaust resources such that other connections or processes on the same machine may also be impacted or crash,” Netflix said in an advisory published on GitHub.

The vulnerabilities have been dubbed Data Dribble (CVE-2019-9511), Ping Flood (CVE-2019-9512), Resource Loop (CVE-2019-9513), Reset Flood (CVE-2019-9514), Settings Flood (CVE-2019-9515), 0-Length Headers Leak (CVE-2019-9516), Internal Data Buffering (CVE-2019-9517), and Empty Frames Flood (CVE-2019-9518). CVE-2019-9518 was discovered by Piotr Sikora of Google, while the rest were identified by Jonathan Looney of Netflix.

All of the flaws are variations of the same attack, where a malicious client contacts the server in an effort to get it to generate a response. However, the client refuses to read the response, which triggers the server’s queue management code. If the queue is not handled properly, the server can end up consuming an excessive amount of memory and CPU resources, which can result in a DoS condition.

The list of vendors confirmed to be impacted includes Amazon, Apple, Facebook and Microsoft. Intel and MicroTik are not affected, and there is a list of 200 other entities for which CERT/CC has listed impact as “unknown.”

Microsoft, Apple, Cloudflare, NGINX, and Akamai have already released patches for the vulnerabilities. As a workaround, users can disable HTTP/2 support on their servers if possible, but Netflix pointed out that this could cause performance issues.

Related: High-Profile Vulnerabilities Affect HTTP/2

Related: Windows Servers Vulnerable to DoS Attacks, Microsoft Warns

Written By

Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.

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