HTTP/2 Rapid reset attack The HTTP/2 protocol allows clients to indicate to the server that a previous stream should be canceled by sending a RSTSTREAM frame. The protocol does not require the client and server to coordinate the cancellation in any way, the client may do it unilaterally. The client may also assume that the cancellation will take effect immediately when the server receives the RSTSTREAM frame, before any other data from that TCP connection is processed.

Abuse of this feature is called a Rapid Reset attack because it relies on the ability for an endpoint to send a RSTSTREAM frame immediately after sending a request frame, which makes the other endpoint start working and then rapidly resets the request. The request is canceled, but leaves the HTTP/2 connection open.

The HTTP/2 Rapid Reset attack built on this capability is simple: The client opens a large number of streams at once as in the standard HTTP/2 attack, but rather than waiting for a response to each request stream from the server or proxy, the client cancels each request immediately.

The ability to reset streams immediately allows each connection to have an indefinite number of requests in flight. By explicitly canceling the requests, the attacker never exceeds the limit on the number of concurrent open streams. The number of in-flight requests is no longer dependent on the round-trip time (RTT), but only on the available network bandwidth.

In a typical HTTP/2 server implementation, the server will still have to do significant amounts of work for canceled requests, such as allocating new stream data structures, parsing the query and doing header decompression, and mapping the URL to a resource. For reverse proxy implementations, the request may be proxied to the backend server before the RSTSTREAM frame is processed. The client on the other hand paid almost no costs for sending the requests. This creates an exploitable cost asymmetry between the server and the client.

Multiple software artifacts implementing HTTP/2 are affected. This advisory was originally ingested from the swift-nio-http2 repo advisory and their original conent follows.

swift-nio-http2 specific advisory swift-nio-http2 is vulnerable to a denial-of-service vulnerability in which a malicious client can create and then reset a large number of HTTP/2 streams in a short period of time. This causes swift-nio-http2 to commit to a large amount of expensive work which it then throws away, including creating entirely new Channels to serve the traffic. This can easily overwhelm an EventLoop and prevent it from making forward progress.

swift-nio-http2 1.28 contains a remediation for this issue that applies reset counter using a sliding window. This constrains the number of stream resets that may occur in a given window of time. Clients violating this limit will have their connections torn down. This allows clients to continue to cancel streams for legitimate reasons, while constraining malicious actors.

A flaw named SegmentSmack was found in the way the Linux kernel handled specially crafted TCP packets. A remote attacker could use this flaw to trigger time and calculation expensive calls to tcpcollapseofoqueue() and tcppruneofoqueue() functions by sending specially modified packets within ongoing TCP sessions which could lead to a CPU saturation and hence a denial of service on the system. Maintaining the denial of service condition requires continuous two-way TCP sessions to a reachable open port, thus the attacks cannot be performed using spoofed IP addresses.

A vulnerability in the received packet parser of Cisco Expressway Series and Cisco TelePresence Video Communication Server (VCS) software could allow an unauthenticated, remote attacker to cause a reload of the affected system, resulting in a denial of service (DoS) condition. The vulnerability is due to insufficient size validation of user-supplied data. An attacker could exploit this vulnerability by sending crafted H.224 data in Real-Time Transport Protocol (RTP) packets in an H.323 call. An exploit could allow the attacker to overflow a buffer in a cache that belongs to the received packet parser, which will result in a crash of the application, resulting in a DoS condition. All versions of Cisco Expressway Series Software and Cisco TelePresence VCS Software prior to version X8.8.2 are vulnerable. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. Cisco Bug IDs: CSCus99263.

The Expressway component in Cisco TelePresence Video Communication Server (VCS) uses the same default X.509 certificate across different customers' installations, which makes it easier for remote attackers to conduct man-in-the-middle attacks against SSL sessions by leveraging the certificate's trust relationship, aka Bug ID CSCue07471.

A vulnerability in the web-based management interface of Cisco Expressway Series and Cisco TelePresence Video Communication Server (VCS) could allow an authenticated, remote attacker with read-write privileges on the application to perform a command injection attack that could result in remote code execution on an affected device. This vulnerability is due to insufficient validation of user-supplied input. An attacker could exploit this vulnerability by sending a crafted request to the web-based management interface of an affected device. A successful exploit could allow the attacker to establish a remote shell with root privileges.

A vulnerability in the REST API of Cisco Expressway Series and Cisco TelePresence VCS could allow an unauthenticated, remote attacker to conduct a cross-site request forgery (CSRF) attack on an affected system. This vulnerability is due to insufficient CSRF protections for the web-based management interface of an affected system. An attacker could exploit this vulnerability by persuading a user of the REST API to follow a crafted link. A successful exploit could allow the attacker to cause the affected system to reload. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. 

A vulnerability in the Session Initiation Protocol (SIP) on the Cisco TelePresence Video Communication Server (VCS) could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on the targeted appliance. The vulnerability is due to excessive SIP traffic sent to the device. An attacker could exploit this vulnerability by transmitting large volumes of SIP traffic to the VCS. An exploit could allow the attacker to cause a complete DoS condition on the targeted system. Cisco Bug IDs: CSCve32897.

Cisco TelePresence Video Communication Server (VCS) X7.0.3 does not properly process certain search rules, which allows remote attackers to create conferences via an unspecified Conductor request, aka Bug ID CSCub67989.

Cisco TelePresence Video Communication Server (VCS) and Expressway Software before X8.2 allow remote attackers to cause a denial of service (device reload) via a high rate of crafted packets, aka Bug ID CSCui06507.

The SIP IX implementation in Cisco TelePresence Video Communication Server (VCS) and Expressway Software before X8.1.1 allows remote attackers to cause a denial of service (device reload) via crafted SDP packets, aka Bug ID CSCuo42252.

Cisco TelePresence Video Communication Server (VCS) and Expressway Software before X8.1.1 allow remote attackers to cause a denial of service (device reload) via crafted SIP packets, aka Bug IDs CSCum60442 and CSCum60447.

Cross-site scripting (XSS) vulnerability in Cisco TelePresence Video Communication Server (VCS) X8.5.1 allows remote attackers to inject arbitrary web script or HTML via a crafted URL, aka Bug ID CSCut27635.

Cisco TelePresence Video Communication Server (VCS) and Cisco Expressway allow remote attackers to cause a denial of service (memory and CPU consumption, and partial outage) via crafted SIP packets, aka Bug ID CSCur12473.

The Mobile and Remote Access (MRA) component in Cisco TelePresence Video Communication Server (VCS) X8.1 through X8.7 and Expressway X8.1 through X8.6 mishandles certificates, which allows remote attackers to bypass authentication via an arbitrary trusted certificate, aka Bug ID CSCuz64601.

Multiple vulnerabilities in the API and in the web-based management interface of Cisco Expressway Series and Cisco TelePresence Video Communication Server (VCS) could allow a remote attacker to overwrite arbitrary files or conduct null byte poisoning attacks on an affected

Multiple vulnerabilities in the API and web-based management interfaces of Cisco Expressway Series and Cisco TelePresence Video Communication Server (VCS) could allow an authenticated, remote attacker to write files or disclose sensitive information on an affected device. For more information about these vulnerabilities, see the Details section of this advisory. Cisco has released software updates that address these vulnerabilities. There are no workarounds that address these vulnerabilities. This advisory is available at the following link:https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-expressway-filewrite-bsFVwueV

Multiple vulnerabilities in the API and in the web-based management interface of Cisco Expressway Series Software and Cisco TelePresence Video Communication Server (VCS) Software could allow a remote attacker to bypass certificate validation or conduct cross-site request forgery attacks on an affected device. Note: Cisco Expressway Series refers to the Expressway Control (Expressway-C) device and the Expressway Edge (Expressway-E) device. For more information about these vulnerabilities, see the Details section of this advisory. Cisco has released software updates that address these vulnerabilities. There are no workarounds that address these vulnerabilities. This advisory is available at the following link:https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-expressway-csrf-sqpsSfY6

Multiple vulnerabilities in the API and web-based management interfaces of Cisco Expressway Series and Cisco TelePresence Video Communication Server (VCS) could allow an authenticated, remote attacker with read/write privileges to the application to write files or execute arbitrary code on the underlying operating system of an affected device as the root user. For more information about these vulnerabilities, see the Details section of this advisory. Cisco has released software updates that address these vulnerabilities. There are no workarounds that address these vulnerabilities. This advisory is available at the following link:https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-expressway-filewrite-87Q5YRk