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 authentication bypass by primary weakness vulnerability in Fortinet FortiOS 8.0.0 through 8.0.1, FortiOS 7.6.0 through 7.6.7, FortiOS 7.4.0 through 7.4.12, FortiOS 7.2.0 through 7.2.13 may allow an unauthenticated attacker to broadcast LSA via specially crafted request

A improper certificate validation vulnerability in Fortinet FortiAnalyzer 8.0.0 through 8.0.1, FortiAnalyzer 7.6.0 through 7.6.7, FortiAnalyzer 7.4.0 through 7.4.11, FortiAnalyzer 7.2 all versions, FortiAnalyzer Cloud 8.0.1, FortiAnalyzer Cloud 7.6.0 through 7.6.7, FortiAnalyzer Cloud 7.4.1 through 7.4.11, FortiAnalyzer Cloud 7.2 all versions, FortiManager 8.0.0 through 8.0.1, FortiManager 7.6.0 through 7.6.7, FortiManager 7.4.0 through 7.4.11, FortiManager 7.2 all versions, FortiManager Cloud 8.0.1, FortiManager Cloud 7.6.0 through 7.6.7, FortiManager Cloud 7.4.1 through 7.4.11, FortiManager Cloud 7.2 all versions may allow a MITM attacker to impersonate the radius server via a rogue RADIUS server.

A improper limitation of a pathname to a restricted directory ('path traversal') vulnerability in Fortinet FortiAnalyzer 8.0.0 through 8.0.1, FortiAnalyzer 7.6.2 through 7.6.7, FortiAnalyzer 7.4.7 through 7.4.11, FortiAnalyzer 7.2.10 through 7.2.12, FortiAnalyzer Cloud 8.0.0 through 8.0.1, FortiAnalyzer Cloud 7.6.0 through 7.6.7, FortiAnalyzer Cloud 7.4.1 through 7.4.11, FortiAnalyzer Cloud 7.2.1 through 7.2.12, FortiManager 8.0.0 through 8.0.1, FortiManager 7.6.2 through 7.6.7, FortiManager 7.4.7 through 7.4.11, FortiManager 7.2.10 through 7.2.12, FortiManager Cloud 8.0.0 through 8.0.1, FortiManager Cloud 7.6.0 through 7.6.7, FortiManager Cloud 7.4.1 through 7.4.11, FortiManager Cloud 7.2.1 through 7.2.12 may allow an authenticated administrator to write arbitrary files via a specially crafted archive.

A improper neutralization of special elements used in a template engine vulnerability in Fortinet FortiAnalyzer 8.0.0, FortiAnalyzer Cloud 8.0.0, FortiManager 8.0.0, FortiManager Cloud 8.0.0 may allow an authenticated attacker with restricted privileges to execute unauthorized code or commands via a specially crafted request.

A authorization bypass through user-controlled key vulnerability in Fortinet FortiAnalyzer 8.0.0 through 8.0.1, FortiAnalyzer 7.6.0 through 7.6.7, FortiAnalyzer 7.4.0 through 7.4.11, FortiAnalyzer 7.2 all versions, FortiAnalyzer Cloud 8.0.1, FortiAnalyzer Cloud 7.6.0 through 7.6.7, FortiAnalyzer Cloud 7.4.1 through 7.4.11, FortiAnalyzer Cloud 7.2 all versions, FortiManager 8.0.0 through 8.0.1, FortiManager 7.6.0 through 7.6.7, FortiManager 7.4.0 through 7.4.11, FortiManager 7.2 all versions, FortiManager Cloud 8.0.1, FortiManager Cloud 7.6.0 through 7.6.7, FortiManager Cloud 7.4.1 through 7.4.11, FortiManager Cloud 7.2 all versions may allow an authenticated administrator to access to other VDOMs via specially crafted HTTP requests.

A improper neutralization of argument delimiters in a command ('argument injection') vulnerability in Fortinet FortiAnalyzer 8.0.0, FortiAnalyzer 7.6.0 through 7.6.7, FortiAnalyzer 7.4.0 through 7.4.11, FortiAnalyzer 7.2.0 through 7.2.12, FortiAnalyzer Cloud 8.0.0, FortiAnalyzer Cloud 7.6.0 through 7.6.7, FortiAnalyzer Cloud 7.4.1 through 7.4.11, FortiAnalyzer Cloud 7.2.1 through 7.2.12, FortiManager 8.0.0, FortiManager 7.6.0 through 7.6.7, FortiManager 7.4.0 through 7.4.11, FortiManager 7.2.0 through 7.2.12, FortiManager Cloud 8.0.0, FortiManager Cloud 7.6.0 through 7.6.7, FortiManager Cloud 7.4.1 through 7.4.11, FortiManager Cloud 7.2.1 through 7.2.12 may allow an authenticated privileged admin user to execute unauthorized code or commands.

A improper limitation of a pathname to a restricted directory ('path traversal') vulnerability in Fortinet FortiAnalyzer 8.0.0 through 8.0.1, FortiAnalyzer 7.6.3 through 7.6.7, FortiAnalyzer Cloud 8.0.0 through 8.0.1, FortiAnalyzer Cloud 7.6.3 through 7.6.7, FortiManager 8.0.0 through 8.0.1, FortiManager 7.6.3 through 7.6.7, FortiManager Cloud 8.0.0 through 8.0.1, FortiManager Cloud 7.6.3 through 7.6.7 may allow an authenticated attacker with admin privileges to execute unauthorized code or commands via crafted requests.

A improper limitation of a pathname to a restricted directory ('path traversal') vulnerability in Fortinet FortiAnalyzer 8.0.0, FortiAnalyzer 7.6.0 through 7.6.7, FortiAnalyzer 7.4.0 through 7.4.11, FortiAnalyzer Cloud 8.0.0, FortiAnalyzer Cloud 7.6.0 through 7.6.7, FortiAnalyzer Cloud 7.4.1 through 7.4.11, FortiManager 8.0.0, FortiManager 7.6.0 through 7.6.7, FortiManager 7.4.0 through 7.4.11, FortiManager Cloud 8.0.0, FortiManager Cloud 7.6.0 through 7.6.7, FortiManager Cloud 7.4.1 through 7.4.11 may allow an authenticated administrator to read or write arbitrary files or execute unauthorized code or commands via specially crafted requests to the GUI.

A authorization bypass through user-controlled key vulnerability in Fortinet FortiManager 8.0.0 through 8.0.1, FortiManager 7.6.0 through 7.6.7, FortiManager 7.4.0 through 7.4.11 may allow a remote authenticated attacker with admin permission to elevate their privileges to root via crafted HTTP requests.

A improper neutralization of special elements in output used by a downstream component ('injection') vulnerability in Fortinet FortiManager 8.0.0, FortiManager 7.6.0 through 7.6.7, FortiManager 7.4.0 through 7.4.11 may allow an authenticated administrator to read or write arbitrary files or execute unauthorized code or commands via specially crafted requests to the GUI.

A improper neutralization of special elements in output used by a downstream component ('injection') vulnerability in Fortinet FortiAnalyzer 8.0.0, FortiAnalyzer 7.6.0 through 7.6.7, FortiAnalyzer 7.4.0 through 7.4.11, FortiAnalyzer Cloud 8.0.0, FortiAnalyzer Cloud 7.6.0 through 7.6.7, FortiAnalyzer Cloud 7.4.1 through 7.4.11, FortiManager 8.0.0, FortiManager 7.6.0 through 7.6.7, FortiManager 7.4.0 through 7.4.11, FortiManager Cloud 8.0.0, FortiManager Cloud 7.6.0 through 7.6.7, FortiManager Cloud 7.4.1 through 7.4.11 may allow an authenticated administrator to read or write arbitrary files or execute unauthorized code or commands via specially crafted requests to the GUI.

A Heap-based Buffer Overflow vulnerability [CWE-122] in FortiManager, FortiManager Cloud, FortiAnalyzer and FortiAnalyzer Cloud may allow an authenticated administrator to execute unauthorized code or commands or cause a denial of service via specially crafted JSON-RPC requests.

A authorization bypass through user-controlled key vulnerability in Fortinet FortiManager 8.0.0 through 8.0.1, FortiManager 7.6.0 through 7.6.7, FortiManager 7.4.0 through 7.4.11, FortiManager 7.2.0 through 7.2.12, FortiManager Cloud 8.0.1, FortiManager Cloud 7.6.0 through 7.6.7, FortiManager Cloud 7.4.1 through 7.4.11, FortiManager Cloud 7.2.1 through 7.2.12 may allow an authenticated attacker to execute commands outside of the expected scope via specially crafted HTTP request.

A Code Injection vulnerability [CWE-94] in FortiManager, FortiManager Cloud, FortiAnalyzer and FortiAnalyzer Cloud may allow an authenticated administrator to execute unauthorized code or commands via specially crafted requests.

A authentication bypass by spoofing vulnerability in Fortinet FortiAnalyzer 8.0.0 through 8.0.1, FortiAnalyzer 7.6.0 through 7.6.7, FortiAnalyzer 7.4.0 through 7.4.11, FortiAnalyzer 7.2.0 through 7.2.12, FortiAnalyzer Cloud 8.0.1, FortiAnalyzer Cloud 7.6.0 through 7.6.7, FortiAnalyzer Cloud 7.4.1 through 7.4.11, FortiAnalyzer Cloud 7.2.1 through 7.2.12, FortiManager 8.0.0 through 8.0.1, FortiManager 7.6.0 through 7.6.7, FortiManager 7.4.0 through 7.4.11, FortiManager 7.2.0 through 7.2.12, FortiManager Cloud 8.0.1, FortiManager Cloud 7.6.0 through 7.6.7, FortiManager Cloud 7.4.1 through 7.4.11, FortiManager Cloud 7.2.1 through 7.2.12 may allow an attacker to disrupt the HA state.

A improper control of generation of code ('code injection') vulnerability in Fortinet FortiManager 8.0.0 through 8.0.1, FortiManager 7.6.0 through 7.6.7, FortiManager 7.4.0 through 7.4.11, FortiManager 7.2.0 through 7.2.12, FortiManager Cloud 8.0.0 through 8.0.1, FortiManager Cloud 7.6.0 through 7.6.7, FortiManager Cloud 7.4.1 through 7.4.11, FortiManager Cloud 7.2.1 through 7.2.12 may allow a remote authenticated attacker to execute unauthorized code or commands via crafted HTTP requests.

A Heap-based Buffer Overflow vulnerability [CWE-122] in FortiManager, FortiAnalyzer, FortiManager Cloud and FortiAnalyzer Cloud may allow an authenticated attacker with admin privileges to execute unauthorized code or commands via a crafted request.

A improper encoding or escaping of output vulnerability in Fortinet FortiAnalyzer 8.0.0 through 8.0.2, FortiAnalyzer 7.6.0 through 7.6.7, FortiAnalyzer Cloud 8.0.1 through 8.0.2, FortiAnalyzer Cloud 7.6.0 through 7.6.7, FortiAnalyzer-BigData 7.6.0 through 7.6.2, FortiManager 8.0.0 through 8.0.2, FortiManager 7.6.0 through 7.6.7, FortiManager Cloud 8.0.1 through 8.0.2, FortiManager Cloud 7.6.0 through 7.6.7 may allow an unauthenticated attacker to execute unauthorized code or commands via a specially crafted HTTP request

A Use of Externally-Controlled Format String [CWE-134] in FortiManager, FortiAnalyzer, FortiManager Cloud and FortiAnalyzer Cloud API may allow an authenticated attacker to execute unauthorized commands via specially crafted HTTP request

Summary

Terrapin is a prefix truncation attack targeting the SSH protocol. More precisely, Terrapin breaks the integrity of SSH's secure channel. By carefully adjusting the sequence numbers during the handshake, an attacker can remove an arbitrary amount of messages sent by the client or server at the beginning of the secure channel without the client or server noticing it.

Mitigations

To mitigate this protocol vulnerability, OpenSSH suggested a so-called "strict kex" which alters the SSH handshake to ensure a Man-in-the-Middle attacker cannot introduce unauthenticated messages as well as convey sequence number manipulation across handshakes.

Warning: To take effect, both the client and server must support this countermeasure.

As a stop-gap measure, peers may also (temporarily) disable the affected algorithms and use unaffected alternatives like AES-GCM instead until patches are available.

Details

The SSH specifications of ChaCha20-Poly1305 (chacha20-poly1305@openssh.com) and Encrypt-then-MAC (-etm@openssh.com MACs) are vulnerable against an arbitrary prefix truncation attack (a.k.a. Terrapin attack). This allows for an extension negotiation downgrade by stripping the SSHMSGEXTINFO sent after the first message after SSHMSGNEWKEYS, downgrading security, and disabling attack countermeasures in some versions of OpenSSH. When targeting Encrypt-then-MAC, this attack requires the use of a CBC cipher to be practically exploitable due to the internal workings of the cipher mode. Additionally, this novel attack technique can be used to exploit previously unexploitable implementation flaws in a Man-in-the-Middle scenario.

The attack works by an attacker injecting an arbitrary number of SSHMSGIGNORE messages during the initial key exchange and consequently removing the same number of messages just after the initial key exchange has concluded. This is possible due to missing authentication of the excess SSHMSGIGNORE messages and the fact that the implicit sequence numbers used within the SSH protocol are only checked after the initial key exchange.

In the case of ChaCha20-Poly1305, the attack is guaranteed to work on every connection as this cipher does not maintain an internal state other than the message's sequence number. In the case of Encrypt-Then-MAC, practical exploitation requires the use of a CBC cipher; while theoretical integrity is broken for all ciphers when using this mode, message processing will fail at the application layer for CTR and stream ciphers.

For more details see https://terrapin-attack.com.

Impact

This attack targets the specification of ChaCha20-Poly1305 (chacha20-poly1305@openssh.com) and Encrypt-then-MAC (-etm@openssh.com), which are widely adopted by well-known SSH implementations and can be considered de-facto standard. These algorithms can be practically exploited; however, in the case of Encrypt-Then-MAC, we additionally require the use of a CBC cipher. As a consequence, this attack works against all well-behaving SSH implementations supporting either of those algorithms and can be used to downgrade (but not fully strip) connection security in case SSH extension negotiation (RFC8308) is supported. The attack may also enable attackers to exploit certain implementation flaws in a man-in-the-middle (MitM) scenario.

A improper neutralization of input during web page generation ('cross-site scripting') vulnerability in Fortinet FortiSandbox 5.0.0 through 5.0.5, FortiSandbox 4.4.0 through 4.4.8, FortiSandbox 4.2 all versions, FortiSandbox Cloud 5.0.4 through 5.0.5, FortiSandbox PaaS 5.0.4 through 5.0.5 may allow an unauthenticated attacker to perform an XSS attack via social engineering and crafted HTTP requests.

A improper authentication vulnerability in Fortinet FortiOS 7.6.0 through 7.6.6 may allow a remote authenticated attacker to gain improper access control via an invalid token after entering a valid username and password

An improper limitation of a pathname to a restricted directory ('Path Traversal') vulnerability [CWE-22] in FortiManager and FortiAnalyzer API may allow an authenticated attacker whose profile only has read permission to write and delete files from the underlying filesystem via crafted HTTP or HTTPs requests.

A improper authorization vulnerability in Fortinet FortiManager 8.0.0, FortiManager 7.6.0 through 7.6.7, FortiManager 7.4.0 through 7.4.5, FortiManager 7.2.0 through 7.2.8 may allow an unauthenticated attacker that can reach the FGFM port to execute code or commands via crafted FGFM packets.

A origin validation error vulnerability in Fortinet FortiClientMac 7.4.0 through 7.4.7, FortiClientWindows 7.4.0 through 7.4.7, FortiClientWindows 7.2.0 through 7.2.14, FortiClientWindowsPAM 7.4.7, FortiClientWindowsPAM 7.2.14 may allow an unauthorized remote attacker to execute unauthorized code or commands. Successful exploitation requires interaction with the victim.

A improper limitation of a pathname to a restricted directory ('path traversal') vulnerability in Fortinet FortiSIEM 7.5.0, FortiSIEM 7.4 all versions, FortiSIEM 7.3 all versions, FortiSIEM 7.2 all versions, FortiSIEM 7.1 all versions, FortiSIEM 7.0 all versions may allow attacker to execute unauthorized code or commands via specially crafted packets.

A Double Free vulnerability [CWE-415] in FortiOS, FortiProxy and FortiSwitch may allow a local authenticated attacker to crash the newcli daemon via crafted CLI commands.

A improper locking vulnerability in Fortinet FortiOS 8.0.0, FortiOS 7.6.4 through 7.6.6 may allow an unauthenticated attacker with network access to the device to cause a denial of service of the HTTPS management interface via crafted HTTP requests.

A improper validation of certificate with host mismatch vulnerability in Fortinet FortiOS 7.6.1 through 7.6.6, FortiProxy 7.6.2 through 7.6.6 may allow attacker to information disclosure via <insert attack vector here>