CVE-2023-44487

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 RST_STREAM 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 RST_STREAM 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 RST_STREAM 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 RST_STREAM 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.

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2023-44487 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.17.0, 11.0.0-M12, 10.1.14, 9.0.81, 8.5.94, 1.28.0, 9.4.53, 10.0.17, 11.0.17, 12.0.2, 10.5.3); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2023-44487? CVE-2023-44487 is a medium-severity uncontrolled resource consumption vulnerability in golang.org/x/net (go), affecting versions < 0.17.0. It is fixed in 0.17.0, 11.0.0-M12, 10.1.14, 9.0.81, 8.5.94, 1.28.0, 9.4.53, 10.0.17, 11.0.17, 12.0.2, 10.5.3. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2023-44487? CVE-2023-44487 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2023-44487?
   • golang.org/x/net (go) (versions < 0.17.0)
   • org.apache.tomcat.embed:tomcat-embed-core (maven) (versions >= 11.0.0-M1, < 11.0.0-M12)
   • github.com/apple/swift-nio-http2 (swift) (versions < 1.28.0)
   • org.eclipse.jetty.http2:http2-common (maven) (versions >= 9.3.0, < 9.4.53)
   • org.eclipse.jetty.http2:http2-server (maven) (versions >= 9.3.0, < 9.4.53)
   • org.eclipse.jetty.http2:jetty-http2-common (maven) (versions >= 12.0.0, < 12.0.2)
   • org.eclipse.jetty.http2:jetty-http2-server (maven) (versions >= 12.0.0, < 12.0.2)
   • com.typesafe.akka:akka-http-core (maven) (versions < 10.5.3)
   • com.typesafe.akka:akka-http-core_2.13 (maven) (versions < 10.5.3)
   • com.typesafe.akka:akka-http-core_2.12 (maven) (versions < 10.5.3)
   • com.typesafe.akka:akka-http-core_2.11 (maven) (versions <= 10.1.15)
   • org.apache.tomcat:tomcat-coyote (maven) (versions >= 11.0.0-M1, < 11.0.0-M12)
4. Is there a fix for CVE-2023-44487? Yes. CVE-2023-44487 is fixed in 0.17.0, 11.0.0-M12, 10.1.14, 9.0.81, 8.5.94, 1.28.0, 9.4.53, 10.0.17, 11.0.17, 12.0.2, 10.5.3. Upgrade to this version or later.
5. Is CVE-2023-44487 exploitable, and should I be worried? Whether CVE-2023-44487 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2023-44487 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2023-44487?
   • Upgrade golang.org/x/net to 0.17.0 or later
   • Upgrade org.apache.tomcat.embed:tomcat-embed-core to 11.0.0-M12 or later
   • Upgrade org.apache.tomcat.embed:tomcat-embed-core to 10.1.14 or later
   • Upgrade org.apache.tomcat.embed:tomcat-embed-core to 9.0.81 or later
   • Upgrade org.apache.tomcat.embed:tomcat-embed-core to 8.5.94 or later
   • Upgrade github.com/apple/swift-nio-http2 to 1.28.0 or later
   • Upgrade org.eclipse.jetty.http2:http2-common to 9.4.53 or later
   • Upgrade org.eclipse.jetty.http2:http2-common to 10.0.17 or later
   • Upgrade org.eclipse.jetty.http2:http2-common to 11.0.17 or later
   • Upgrade org.eclipse.jetty.http2:http2-server to 9.4.53 or later
   • Upgrade org.eclipse.jetty.http2:http2-server to 10.0.17 or later
   • Upgrade org.eclipse.jetty.http2:http2-server to 11.0.17 or later
   • Upgrade org.eclipse.jetty.http2:jetty-http2-common to 12.0.2 or later
   • Upgrade org.eclipse.jetty.http2:jetty-http2-server to 12.0.2 or later
   • Upgrade com.typesafe.akka:akka-http-core to 10.5.3 or later
   • Upgrade com.typesafe.akka:akka-http-core_2.13 to 10.5.3 or later
   • Upgrade com.typesafe.akka:akka-http-core_2.12 to 10.5.3 or later
   • Upgrade org.apache.tomcat:tomcat-coyote to 11.0.0-M12 or later
   • Upgrade org.apache.tomcat:tomcat-coyote to 10.1.14 or later
   • Upgrade org.apache.tomcat:tomcat-coyote to 9.0.81 or later
   • Upgrade org.apache.tomcat:tomcat-coyote to 8.5.94 or later

Other vulnerabilities in golang.org/x/net