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 security regression (CVE-2006-5051) was discovered in OpenSSH's server (sshd). There is a race condition which can lead sshd to handle some signals in an unsafe manner. An unauthenticated, remote attacker may be able to trigger it by failing to authenticate within a set time period.

A flaw was found in the OpenSSH package. For each ping packet the SSH server receives, a pong packet is allocated in a memory buffer and stored in a queue of packages. It is only freed when the server/client key exchange has finished. A malicious client may keep sending such packages, leading to an uncontrolled increase in memory consumption on the server side. Consequently, the server may become unavailable, resulting in a denial of service attack.

A vulnerability was found in OpenSSH when the VerifyHostKeyDNS option is enabled. A machine-in-the-middle attack can be performed by a malicious machine impersonating a legit server. This issue occurs due to how OpenSSH mishandles error codes in specific conditions when verifying the host key. For an attack to be considered successful, the attacker needs to manage to exhaust the client's memory resource first, turning the attack complexity high.

An attacker with arbitrary read and write capability may be able to bypass Pointer Authentication. Description: The issue was addressed with improved checks. WebKit Bugzilla: 272750

Versions affected: WebKitGTK and WPE WebKit before 2.44.2.

ISC BIND contains a data processing errors vulnerability that could allow remote attackers to cause a denial of service via TKEY queries.

Accessibility. An authorization issue was addressed with improved state management.

Chromium: CVE-2023-5217 Heap buffer overflow in vp8 encoding in libvpx

A type confusion issue was addressed with improved checks. Processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been exploited.

Reference: https://webkitgtk.org/security/WSA-2024-0001.html

Accessibility. A logging issue was addressed with improved data redaction.

A use-after-free issue was addressed with improved memory management. This issue is fixed in Safari 18.4, iOS 18.4 and iPadOS 18.4, iPadOS 17.7.6, macOS Sequoia 15.4, tvOS 18.4, visionOS 2.4, watchOS 11.4. Processing maliciously crafted web content may lead to an unexpected Safari crash.

A permissions issue was addressed with additional restrictions. This issue is fixed in iOS 18.4 and iPadOS 18.4, iPadOS 17.7.7, macOS Sequoia 15.4, macOS Sonoma 14.7.5, tvOS 18.4, watchOS 11.4. An app may be able to read arbitrary file metadata.

Accessibility. A logging issue was addressed with improved data redaction.

A permissions issue was addressed with additional restrictions. This issue is fixed in macOS Sequoia 15.4, macOS Sonoma 14.7.5, macOS Ventura 13.7.5. An app may be able to gain root privileges.

Accessibility. A logging issue was addressed with improved data redaction.

Accessibility. A logging issue was addressed with improved data redaction.

A memory corruption issue was addressed with improved bounds checking. This issue is fixed in iOS 18.4.1 and iPadOS 18.4.1, macOS Sequoia 15.4.1, tvOS 18.4.1, visionOS 2.4.1, watchOS 11.5. Processing an audio stream in a maliciously crafted media file may result in code execution. Apple is aware of a report that this issue may have been exploited in an extremely sophisticated attack against specific targeted individuals on versions of iOS released before iOS 18.4.1.

Apple iOS, iPadOS, macOS, and other Apple products contain an arbitrary read and write vulnerability that allows an attacker to bypass Pointer Authentication.

Accessibility. An authorization issue was addressed with improved state management.

A use after free issue was addressed with improved memory management. This issue is fixed in iOS 18.3 and iPadOS 18.3, iPadOS 17.7.6, macOS Sequoia 15.3, macOS Sonoma 14.7.5, macOS Ventura 13.7.5, tvOS 18.3, visionOS 2.3, watchOS 11.3. A malicious application may be able to elevate privileges. Apple is aware of a report that this issue may have been actively exploited against versions of iOS before iOS 17.2.

A permissions issue was addressed with additional restrictions. This issue is fixed in iOS 18.3 and iPadOS 18.3, macOS Sequoia 15.3, tvOS 18.3, watchOS 11.3. A malicious app may be able to gain root privileges.

A buffer overflow issue was addressed with improved memory handling. This issue is fixed in macOS Sequoia 15.4, macOS Sonoma 14.7.5, macOS Ventura 13.7.5. An app may be able to execute arbitrary code with kernel privileges.

A parsing issue in the handling of directory paths was addressed with improved path validation. This issue is fixed in iOS 18.4 and iPadOS 18.4, macOS Sequoia 15.4, macOS Sonoma 14.7.5, macOS Ventura 13.7.5. An app may be able to gain root privileges.

A validation issue was addressed with improved logic. This issue is fixed in iOS 18.3 and iPadOS 18.3, iPadOS 17.7.4, macOS Sequoia 15.3, macOS Sonoma 14.7.3, tvOS 18.3, visionOS 2.3, watchOS 11.3. An app may be able to execute arbitrary code with kernel privileges.

OpenSSH 4.4 was released and mentions:

Fix an unsafe signal hander reported by Mark Dowd. The signal handler was vulnerable to a race condition that could be exploited to perform a pre-authentication denial of service. On portable OpenSSH, this vulnerability could theoretically lead to pre-authentication remote code execution if GSSAPI authentication is enabled, but the likelihood of successful exploitation appears remote.

This could only affect RHEL4 as previous RHEL did not support GSSAPI