CVE-2026-8711: f5 nginx javascript Heap-based Buffer Overflow

Vulnerability summary

CVE-2026-8711 is a critical (CVSS 9.8) Heap-based Buffer Overflow vulnerability in f5 nginx javascript. EPSS estimates a 0.79% chance of exploitation in the next 30 days, higher than 55.5% of scored vulnerabilities.

Timeline

1. 19-05-2026
   PublishedVulnerability first disclosed.
2. 21-05-2026
   Last modifiedVulnerability information updated.

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.

• CWE-122Heap-based Buffer OverflowA 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().