F5 NGINX Open Source/NGINX Plus up to 1.30.2/1.31.1 heap-based overflow

Summaryinfo

A vulnerability has been found in F5 NGINX Open Source and NGINX Plus up to 1.30.2/1.31.1 and classified as critical. Impacted is an unknown function. This manipulation causes heap-based overflow. This vulnerability is registered as CVE-2026-42055. Remote exploitation of the attack is possible. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability classified as critical was found in F5 NGINX Open Source and NGINX Plus up to 1.30.2/1.31.1. Affected by this vulnerability is an unknown part. The manipulation with an unknown input leads to a heap-based overflow vulnerability. The CWE definition for the vulnerability is CWE-122. A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc(). As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at my.f5.com. This vulnerability is known as CVE-2026-42055 since 06/02/2026. The exploitation appears to be difficult. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 06/18/2026).

Upgrading to version 1.30.3 or 1.31.2 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2026-1995). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

• NGINX NGINX
• NGINX NGINX Plus

Productinfo

Type

• Web Server

Vendor

• F5

Name

• NGINX Open Source
• NGINX Plus

Version

• 1.30.0
• 1.30.1
• 1.30.2
• 1.31.0
• 1.31.1

License

• commercial

Website

• Vendor: https://f5.com/

CPE 2.3info

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CPE 2.2info

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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