Buffer overflow in F5 nginx JavaScript
CVE-2026-8711
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.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.008 (54.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 55th percentile — 54.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.097 · newest: 0.008 · change: -0.089
Affected products
- F5 nginx JavaScript — versions 0.9.4
- F5 Njs
Weakness classification (CWE)
References
- my.f5.com/manage/s/article/K000161307 (vendor-advisory, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-8711?
- CVE-2026-8711 is a high-severity vulnerability in F5 nginx JavaScript, classified under Heap-based Buffer Overflow. CVSS score: 8.1/10. Published 2026-05-19.
- How severe is CVE-2026-8711?
- High severity. CVSS v3 base score is 8.1 out of 10.