On August 13, security researchers at Tel Aviv University disclosed a new HTTP/2 denial-of-service (DoS) vulnerability that they are calling MadeYouReset (CVE-2025-8671). This vulnerability exists in a limited number of unpatched HTTP/2 server implementations that do not sufficiently enforce restrictions on the number of times a client may send malformed frames. If you’re using Cloudflare for HTTP DDoS mitigation, you’re already protected from MadeYouReset.
Cloudflare was informed of this vulnerability in May through a coordinated disclosure process, and we were able to confirm that our systems were not susceptible, due in large part to the mitigations we put in place during Rapid Reset (CVE-2023-44487). MadeYouReset and Rapid Reset are two conceptually similar HTTP/2 protocol attacks that exploit a fundamental feature within the HTTP/2 specification: stream resets. In the HTTP/2 protocol, a “stream” represents an independent series of HTTP request/response pairs exchanged between the client and server within an HTTP/2 connection. The stream reset feature is intended to allow a client to initiate an HTTP request and subsequently cancel it before the server has delivered its response.
The vulnerability exploited by both MadeYouReset and Rapid Reset lies in the potential for malicious actors to abuse this stream reset mechanism. By repeatedly causing stream resets, attackers can overwhelm a server’s resources. While the server is attempting to process and respond to a multitude of requests, the rapid succession of resets forces it to expend computational effort on starting and then immediately discarding these operations. This can lead to resource exhaustion and impact the availability of the targeted server for legitimate users. The difference between MadeYouReset and Rapid Reset is that, instead of clients issuing stream resets directly, they instead trick servers into resetting streams by sending specially crafted malformed frames.
Fortunately, the MadeYouReset vulnerability only impacts a relatively small number of HTTP/2 implementations. In most major HTTP/2 implementations already in widespread use today, the proactive measures taken to counter Rapid Reset in 2023 have also provided substantial protection against MadeYouReset, limiting its potential impact and preventing a similarly disruptive event.
A note about Cloudflare’s Pingora and its users:
Our open-sourced Pingora framework uses the popular Rust-language h2 library for its HTTP/2 support. Versions of h2 prior to 0.4.11 were potentially susceptible to MadeYouReset. Users of Pingora can patch their applications by updating their h2 crate version using the cargo update command. Pingora does not itself terminate inbound HTTP connections to Cloudflare’s network, meaning this vulnerability could not be exploited against Cloudflare’s infrastructure.
We would like to credit researchers Gal Bar Nahum, Anat Bremler-Barr, and Yaniv Harel of Tel Aviv University for discovering this vulnerability and thank them for their leadership in the coordinated disclosure process. Cloudflare always encourages security researchers to submit vulnerabilities like this to our HackerOne Bug Bounty program.
