New HTTP/2 Vulnerability Exposes Web Servers to DoS Attacks

New research has unveiled a vulnerability within the HTTP/2 protocol, known as HTTP/2 CONTINUATION Flood, that allows for denial-of-service (DoS) attacks.

This issue, discovered by security researcher Bartek Nowotarski and reported to CERT/CC on January 25, 2024, arises from improper handling of CONTINUATION frames—a component used to transmit extended header lists within a single stream. CERT/CC’s advisory highlights that attackers exploiting this vulnerability could send continuous CONTINUATION frames without concluding them with an END_HEADERS flag, leading to potential server crashes or significant performance drops due to out-of-memory conditions or CPU exhaustion.

This attack method is particularly insidious as it doesn’t leave traces in HTTP access logs, enabling attackers to disrupt server operations with minimal detectability. The flaw has been identified across several implementations of the HTTP/2 protocol, affecting major projects like Apache HTTP Server, Apache Tomcat, and Node.js among others. Impacted entities are urged to update their software to mitigate this vulnerability.

In instances where updates are unavailable, disabling HTTP/2 temporarily is recommended as a precautionary measure. This discovery emphasizes the critical need for diligent handling and scrutiny of protocol frames to safeguard against such vulnerabilities, which can compromise server availability and security.

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