F5 Patches Two Critical NGINX Open Source Flaws Enabling Remote Code Execution

Summary

F5 has released updates to address two critical vulnerabilities in NGINX Open Source, CVE-2026-42530 and CVE-2026-42055, both rated with a CVSS v4 score of 9.2. These flaws could allow remote, unauthenticated attackers to execute code on affected systems, particularly when ASLR is disabled or bypassed. Patches are available for various NGINX versions, with mitigations including disabling HTTP/3 or reconfiguring specific proxy directives.

Full text

F5 Patches Two Critical NGINX Open Source Flaws Enabling Remote Code Execution Ravie LakshmananJun 18, 2026Vulnerability / Cloud Security F5 has released security updates to address two critical security flaws in NGINX Open Source that could be exploited to achieve code execution on affected systems. The vulnerabilities are listed below - CVE-2026-42530 (CVSS v4 score: 9.2) - A use-after-free vulnerability in the ngx_http_v3_module that could be triggered by a remote unauthenticated attacker when NGINX Open Source is configured to use the HTTP/3 QUIC module to reopen a QPACK encoder stream by means of a specially crafted HTTP/3 session, and execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. CVE-2026-42055 (CVSS v4 score: 9.2) - A heap-based buffer overflow vulnerability in the ngx_http_proxy_v2_module and ngx_http_grpc_module modules that could be triggered by a remote unauthenticated attacker when the proxy_http_version to 2 or grpc_pass directives are used to proxy HTTP/2 traffic, the ignore_invalid_headers directive is set to off, and the large_client_header_buffers directive size is larger than 2 MB, and execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. Both shortcomings have been patched in the following versions - CVE-2026-42530 - NGINX Open Source 1.31.0 - 1.31.1 (Fixed in 1.31.2) NGINX Gateway Fabric 2.0.0 - 2.6.3 (Fixed in 2.6.4) NGINX Gateway Fabric 1.3.0 - 1.6.2 NGINX Instance Manager 2.17.0 - 2.22.0 NGINX Ingress Controller 5.0.0 - 5.5.0 NGINX Ingress Controller 4.0.0 - 4.0.1 NGINX Ingress Controller 3.5.0 - 3.7.2 CVE-2026-42055 - NGINX Plus 37.0.0 - 37.0.1 (Fixed in 37.0.2.1) NGINX Plus R33 - R36 (Fixed in R36 P6) NGINX Open Source 1.31.1 (Fixed in 1.31.2) NGINX Open Source 1.30.0 - 1.30.2 (Fixed in 1.30.3) NGINX Instance Manager 2.17.0 - 2.22.0 F5 WAF for NGINX 5.9.0 - 5.13.1 NGINX App Protect WAF 5.2.0 - 5.8.0 NGINX App Protect WAF 4.10.0 - 4.16.0 F5 DoS for NGINX 4.9.0 NGINX App Protect DoS 4.3.0 - 4.7.0 NGINX Gateway Fabric 2.0.0 - 2.6.3 (Fixed in 2.6.4) NGINX Gateway Fabric 1.3.0 - 1.6.2 NGINX Ingress Controller 5.0.0 - 5.5.0 NGINX Ingress Controller 4.0.0 - 4.0.1 NGINX Ingress Controller 3.5.0 - 3.7.2 As mitigations, F5 has outlined the following actions - CVE-2026-42530 - Disable HTTP/3 CVE-2026-42055 - Remove the ignore_invalid_headers off directive from the configuration, or reduce the large_client_header_buffers directive size below 2 MB Although F5 makes no mention of the vulnerabilities being exploited in the wild, security flaws in F5 products have been repeatedly exploited by bad actors. As recently as last month, another critical security defect in NGINX Plus and NGINX Open Source (CVE-2026-42945, CVSS score: 9.2), also called NGINX Rift, came under active exploitation within days after public disclosure. Found this article interesting? Follow us on Google News, Twitter and LinkedIn to read more exclusive content we post. SHARE     Tweet Share Share Share SHARE  Cloud security, F5 Networks, HTTP/2, HTTP/3, NGINX, remote code execution, Vulnerability, Web Server ⚡ Top Stories This Week Chrome V8 Zero-Day CVE-2026-11645 Exploited in the Wild - Patch Now Researchers Build Self-Replicating AI Worm That Operates Entirely on Local, Open-Weight Models Microsoft Defender RoguePlanet Zero-Day Grants SYSTEM Access on Updated Windows Anthropic Releases Claude Fable 5, Its Most Powerful AI Yet, With Cyber Safeguards Microsoft Patches Record 206 Flaws, Including Three Zero-Days and Critical RCE Bugs Ivanti, Fortinet, and SAP Release Patches for Multiple Critical Vulnerabilities Cybersecurity Stars Awards 2026: Winners Announced Across 95 Categories ThreatsDay Bulletin: Worm Code Leaked, AI Agent Phished, Claude Code Patch + 28 New Stories New GreatXML Exploit Bypasses Windows BitLocker via Recovery Partition XML Files Agentjacking Attack Tricks AI Coding Agents Into Running Malicious Code China-Linked Hackers Backdoored Linux Login Software to Hide for Nearly a Decade Critical Splunk Enterprise Flaw Lets Attackers Run Code Without Authentication U.S. Orders Anthropic to Suspend Fable 5 and Mythos 5 Access for Foreign Nationals Over 400 Arch Linux AUR Packages Hijacked to Deploy Infostealer and eBPF Rootkit Palo Alto Warns of Active Exploitation of PAN-OS GlobalProtect VPN Flaw ⚡ Weekly Recap: Chrome 0-Day, UniFi Exploits, macOS Stealers, VPN Flaw and More ⭐ Featured Resources Get the 2026 Guide to Govern and Secure Enterprise AI Agents at Scale [Watch Demo] See Which Security Gaps Attackers Could Exploit First AI Can’t Stop Every Attack. Learn How Zero Trust Can Block What’s Unknown Have You Outgrown Your MDR? 7 Warning Signs Every CISO Should Check

Indicators of Compromise

• cve — CVE-2026-42530
• cve — CVE-2026-42055

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