CVE-2026-42055: F5 Dos

High severity, CVSS 8.1. EPSS: 6.5% chance of exploitation in the next 30 days.

NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_proxy_v2_module and ngx_http_grpc_module modules. This vulnerability exists 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 megabytes. A remote, unauthenticated attacker, along with conditions beyond their control, could send large headers while creating an upstream request. This may cause a heap-based buffer overflow in the NGINX worker process leading to a restart. Additionally, attackers can execute code on systems with Address Space Layout Randomization (ASLR) disabled or when the attacker can bypass ASLR. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Affected products

• F5 Dos: from 4.3.0, up to and including 4.7.0; version 4.9.0 only
• F5 Nginx Gateway Fabric: from 1.3.0, up to and including 1.6.2; from 2.0.0, up to and including 2.6.3
• F5 Nginx Ingress Controller: from 3.5.0, up to and including 3.7.2; from 4.0.0, up to and including 4.0.1; from 5.0.0, up to and including 5.5.0
• F5 Nginx Instance Manager: from 2.17.0, up to and including 2.22.0
• F5 Nginx Open Source: from 1.0.0, up to and including 1.30.2; from 1.31.0, up to and including 1.31.1
• F5 Nginx Plus: from 37.0.0.1, before 37.0.2.1 (fixed in 37.0.2.1); from r33, before r36 (fixed in r36); version r36 only
• F5 Waf: from 4.10.0, up to and including 4.16.0; from 5.2.0, up to and including 5.8.0; from 5.9.0, up to and including 5.13.1
• Red Hat Discovery: affected versions not specified
• Red Hat Enterprise Linux: version 8.0 only; version 9.0 only; version 10.0 only
• Red Hat Hardened Images: affected versions not specified
• Red Hat Update Infrastructure: from 5.0, before 5.2 (fixed in 5.2)

Published 2026-06-17. Last modified 2026-09-14.