F5 NGINX JavaScript up to 0.9.8 HTTP ngx.fetch heap-based overflow

Summaryinfo

A vulnerability has been found in F5 NGINX JavaScript up to 0.9.8 and classified as critical. The affected element is the function ngx.fetch of the component HTTP Handler. Performing a manipulation results in heap-based overflow. This vulnerability is cataloged as CVE-2026-8711. It is possible to initiate the attack remotely. There is no exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability classified as critical has been found in F5 NGINX JavaScript up to 0.9.8. This affects the function ngx.fetch of the component HTTP Handler. The manipulation with an unknown input leads to a heap-based overflow vulnerability. CWE is classifying the issue as 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(). This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

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.

The advisory is shared at my.f5.com. This vulnerability is uniquely identified as CVE-2026-8711 since 05/15/2026. The exploitability is told to be difficult. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 06/06/2026).

The vulnerability scanner Nessus provides a plugin with the ID 315773 (Linux Distros Unpatched Vulnerability : CVE-2026-8711), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 0.9.9 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (315773) and EUVD (EUVD-2026-30940). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• Web Server

Vendor

• F5

Name

• NGINX JavaScript

Version

• 0.9.0
• 0.9.1
• 0.9.2
• 0.9.3
• 0.9.4
• 0.9.5
• 0.9.6
• 0.9.7
• 0.9.8

License

• commercial

Website

• Vendor: https://f5.com/

CPE 2.3info

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Entryinfo

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

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