CVE-2026-8711

Analyzed Analyzed - Analysis Complete

Heap Buffer Overflow in NGINX JavaScript

Publication date: 2026-05-19

Last updated on: 2026-06-04

Assigner: F5 Networks

Description

NGINX JavaScript has a vulnerability when the js_fetch_proxy directive is configured with at least one client-controlled NGINX variable (for example, $http_*, $arg_*, $cookie_*) and a location invoking the ngx.fetch() operation from NGINX JavaScript. An unauthenticated attacker can exploit this vulnerability by sending crafted HTTP requests. This may cause a heap 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.

CVSS Scores

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Meta Information

Published

2026-05-19

Last Modified

2026-06-04

Generated

2026-06-30

AI Q&A

2026-05-19

EPSS Evaluated

2026-06-28

NVD

CVE-2026-8711

EUVD

EUVD-2026-30940

Affected Vendors & Products

Vendor	Product	Version / Range
f5	njs	From 0.9.4 (inc) to 0.9.9 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
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().

Attack-Flow Graph

Executive Summary

This vulnerability exists in NGINX JavaScript when the js_fetch_proxy directive is configured with at least one client-controlled NGINX variable, such as $http_*, $arg_*, or $cookie_*, and a location uses the ngx.fetch() operation.

An unauthenticated attacker can exploit this by sending specially crafted HTTP requests, which may cause a heap buffer overflow in the NGINX worker process, potentially leading to a process restart.

Furthermore, on systems where Address Space Layout Randomization (ASLR) is disabled, this vulnerability could allow the attacker to execute arbitrary code.

Impact Analysis

The vulnerability can impact you by causing the NGINX worker process to crash and restart, leading to potential denial of service.

On systems without ASLR enabled, an attacker could exploit this vulnerability to execute arbitrary code, which could compromise the security and integrity of your system.

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