May 20, 2024

HTTP/2 CONTINUATION Flood Vulnerability Exposes Web Servers to Denial-of-Service Attacks

In the rapidly evolving world of cybersecurity, a new threat has emerged, targeting the very foundation of web communication - the HTTP/2 protocol. Known as the HTTP/2 CONTINUATION Flood vulnerability, this threat has stirred significant concern within the cybersecurity community, necessitating swift action to minimize the risk of potential denial-of-service (DOS) attacks. This blog sheds light on the intricacies of this vulnerability, explores its impact, and provides essential measures to fortify your defenses.

Understanding HTTP/2 CONTINUATION Flood Vulnerability

The vulnerability stems from the mishandling of the CONTINUATION frame within the HTTP/2 protocol, which was initially designed to optimize web communication efficiency. This specific frame allows for the sequential transmission of header block fragments, playing a crucial role in the seamless operation of HTTP/2 communications. However, an inherent flaw in the processing of these frames has exposed servers to a wide range of potential DoS attacks.

Security researcher Bartek Nowotarski first discovered and reported this issue to the CERT Coordination Center on January 25, 2024. The vulnerability arises from the inadequate handling of multiple CONTINUATION frames sent within a single stream, a scenario that has not been effectively addressed in numerous HTTP/2 implementations. Exploiting this flaw, an attacker can inundate a server with these frames, triggering memory overflow, CPU exhaustion, or even causing the server to crash entirely.

At the core of this vulnerability is the uncontrolled accumulation of CONTINUATION frames within the server's memory. When these frames are transmitted without the END_HEADERS flag, they generate an uninterrupted flow of headers that the server strives to analyze and store. As a consequence, the server's resources can rapidly dwindle, leading to a range of service disruptions, ranging from degraded performance to complete unavailability.

Mitigation Strategies

To effectively tackle the HTTP/2 CONTINUATION Flood vulnerability, a comprehensive approach is essential. The initial step is to promptly update any affected software to the latest versions, as developers have released patches specifically addressing these vulnerabilities. In situations where immediate updates are unavailable, or as a temporary measure, disabling HTTP/2 can serve as a necessary mitigation strategy.

Additionally, it is crucial to implement rate limiting mechanisms and ensure proper memory management within HTTP/2 implementations. These measures play a vital role in minimizing the risk of exploitation. Furthermore, conducting network monitoring to detect any unusual patterns of CONTINUATION frames can provide early indications of potential attacks, allowing for timely intervention and prevention.

Nexusguard Remains Unaffected by the Vulnerability

Nexusguard products, powered by our proprietary software and advanced technology, remain unaffected by the HTTP/2 CONTINUATION flood vulnerability. Our products are hardened with robust security measures to establish a secure environment, offering the following capabilities:

Buffer Protection 

Through setting a maximum limit on CONTINUATION frames and promptly dropping connections upon breach, we prevent buffer overflow situations caused by an influx of CONTINUATION frames, effectively safeguarding our services against potential crashes and disruptions.

Timeout Protection

To maintain optimal performance and protect against prolonged connections, we implement timeout protection. If a connection surpasses the specified timeout duration, we automatically terminate it, thereby averting resource exhaustion and maintaining system efficiency.

Slow Rate Attack Mitigation

Some behaviors associated with HTTP/2 CONTINUATION exhibit similarities to Slow Rate attacks. To counter these threats, we incorporate Slow Rate features that proficiently mitigate such attacks. Through meticulous management of incoming request rates, we successfully neutralize the potential impact of Slow Rate attacks, ensuring the stability and uninterrupted availability of our services.

Safeguarding Your Organization

The discovery of the HTTP/2 CONTINUATION Flood vulnerability serves as a reminder of the ongoing cat-and-mouse game between cybersecurity professionals and malicious threat actors. However, organizations can navigate these turbulent waters and secure their digital assets against emerging threats by staying informed, promptly applying patches, and following best practices for web server configuration.

Leveraging Nexusguard's Application Protection, organizations gain access to a formidable security solution that offers extensive defense against a wide range of attacks across multiple layers, including L3-L4 and L7. With this robust solution in place, organizations can rest assured knowing that their applications are shielded with the highest level of efficiency and effectiveness, even when facing potential zero-day attacks. Nexusguard's Application Protection ensures comprehensive protection, empowering organizations to safeguard their valuable assets with confidence.

To learn more, visit Nexusguard's Application Protection page or contact us via our contact form.

Rest easy knowing that our products remain unaffected by the HTTP/2 CONTINUATION Flood vulnerability. With robust security measures, including buffer protection, timeout protection, and slow rate attack mitigation, Nexusguard safeguards your applications against emerging threats.

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