A critical NGINX vulnerability could let attackers crash servers or execute code. F5 urges users to update immediately.

Administrators running NGINX Open Source or NGINX Plus are being urged to update their systems after the disclosure of a critical security flaw that could allow attackers to crash web servers or potentially execute malicious code remotely.

The vulnerability, tracked as CVE-2026-42533, was disclosed by F5 in July 2026. The company warned that successful exploitation could result in a denial-of-service (DoS) attack by crashing NGINX worker processes and, in certain environments, may even lead to remote code execution (RCE).

According to F5, the issue is caused by a heap buffer overflow in the NGINX worker process. An attacker can exploit the flaw by sending specially crafted HTTP requests to a vulnerable server, with no authentication required. Because NGINX is widely used to power websites, reverse proxies, load balancers and APIs, internet-facing systems are considered the most exposed.

Security researchers noted that while the most likely outcome of an attack is a server crash, the vulnerability could also be leveraged for remote code execution under specific conditions. Although there is no evidence that the flaw has been exploited in the wild, organizations are encouraged to patch affected systems before attackers begin developing exploits.

The vulnerability affects both NGINX Open Source and NGINX Plus. F5 has released updates addressing the issue and recommends administrators upgrade to one of the following fixed versions:

NGINX Open Source 1.30.4
NGINX Open Source 1.31.3
NGINX Plus Release 37 Patch 1 (R37 P1)

Organizations unable to update immediately should closely monitor their servers for unexpected crashes or unusual activity while prioritizing patch deployment as soon as possible.

With NGINX serving millions of websites and enterprise applications worldwide, vulnerabilities affecting the platform are often closely watched by cyber-criminals. Public disclosures of critical flaws can quickly lead to proof-of-concept exploits, making prompt patching one of the most effective ways to reduce risk.

F5 said customers should install the latest available updates without delay and ensure internet-facing systems are running supported versions of the software.

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Critical NGINX Flaw Could Crash Servers