CVE-2026-42055

Published Jun 17, 2026

Last updated 8 days ago

CVSS critical 9.2

Openresty

web application

Server

Port (443)

HTTP

Overview

AI description

Automated description summarized from trusted sources.

CVE-2026-42055 is a vulnerability affecting NGINX Plus and NGINX Open Source, specifically within the `ngx_http_proxy_v2_module` and `ngx_http_grpc_module` modules. This flaw occurs under a specific set of non-default configurations: when `proxy_http_version` is set to 2 or `grpc_pass` directives are used for proxying HTTP/2 traffic, the `ignore_invalid_headers` directive is set to `off`, and the `large_client_header_buffers` directive size exceeds 2 megabytes. Under these conditions, a remote, unauthenticated attacker can send large headers while creating an upstream request. This action can trigger a heap-based buffer overflow within the NGINX worker process, potentially leading to a restart of the process. Additionally, attackers may be able to execute code on systems where Address Space Layout Randomization (ASLR) is disabled or can be bypassed.

Description: 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.
Source: f5sirt@f5.com
NVD status: Modified
Products: dos, nginx_gateway_fabric, nginx_ingress_controller, nginx_instance_manager, nginx_open_source, nginx_plus, waf, discovery, hardened_images, update_infrastructure, enterprise_linux

Risk scores

CVSS 4.0

Type: Secondary
Base score: 9.2
Impact score: -
Exploitability score: -
Vector string: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Severity: CRITICAL

CVSS 3.1

Type: Secondary
Base score: 8.1
Impact score: 5.9
Exploitability score: 2.2
Vector string: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Severity: HIGH

Weaknesses

f5sirt@f5.com: CWE-122
nvd@nist.gov: CWE-787
0b0ca135-0b70-47e7-9f44-1890c2a1c46c: CWE-131

Hype score: Not currently trending

Configurations

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References

Sources include official advisories and independent security research.