Heap-based buffer overflow in NGINX JavaScript - CVE-2026-8711
Published: May 20, 2026
Vulnerability identifier: #VU131922
CSH Severity: High
CVSS v4: 9.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-8711
CWE-ID: CWE-122
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service or execute arbitrary code.
The vulnerability exists due to heap-based buffer overflow in the ngx_http_js_module module when processing crafted HTTP requests that reach a location invoking ngx.fetch() with the js_fetch_proxy directive configured with at least one client-controlled NGINX variable. A remote attacker can send crafted HTTP requests to cause a denial of service or execute arbitrary code.
Code execution is possible on systems with Address Space Layout Randomization disabled. There is no control plane exposure; this is a data plane issue only.
Affected software
NGINX JavaScript
Ubuntu
libnginx-mod-http-js (Ubuntu package)
njs (Ubuntu package)
libnginx-mod-stream-js (Ubuntu package)
Ubuntu
libnginx-mod-http-js (Ubuntu package)
njs (Ubuntu package)
libnginx-mod-stream-js (Ubuntu package)
How to mitigate CVE-2026-8711
Install security update from vendor's website.
NGINX JavaScript - update to 0.9.9
libnginx-mod-http-js (Ubuntu package) - update to 0.9.4-1ubuntu0.1~esm1
njs (Ubuntu package) - update to 0.9.4-1ubuntu0.1~esm1
libnginx-mod-stream-js (Ubuntu package) - update to 0.9.4-1ubuntu0.1~esm1
libnginx-mod-http-js (Ubuntu package) - update to 0.9.4-1ubuntu0.1~esm1
njs (Ubuntu package) - update to 0.9.4-1ubuntu0.1~esm1
libnginx-mod-stream-js (Ubuntu package) - update to 0.9.4-1ubuntu0.1~esm1