# NGINX flaw in Hitachi e-mesh EMS risks DoS

Published: 2026-07-07 · Severity: medium · Sectors: energy
Canonical: https://vorant.io/reports/517d0623-b9af-529a-8990-9d5fff679a5d/nginx-flaw-in-hitachi-e-mesh-ems-risks-dos

> An NGINX rewrite-module heap buffer overflow affects Hitachi Energy e-mesh EMS, potentially enabling denial of service or code execution on energy sector systems.

Hitachi Energy has disclosed a buffer overflow vulnerability in its e-mesh EMS product stemming from bundled NGINX Plus and NGINX Open Source components. The flaw resides in the ngx_http_rewrite_module and can be triggered when a rewrite directive is followed by another rewrite, if, or set directive combined with an unnamed PCRE capture and a replacement string containing a question mark. An unauthenticated attacker able to send crafted HTTP requests could cause a heap buffer overflow in the NGINX worker process, leading to a worker restart (denial of service) and, under certain conditions such as disabled or bypassed ASLR, potential arbitrary code execution.

The vulnerability affects e-mesh EMS versions 4.1.6, 4.4.2, and 4.7.0 running NGINX v1.30.0 and below. Hitachi Energy recommends applying vendor hotfixes to upgrade NGINX to v1.30.2 or later, ensuring rewrite configurations avoid question marks replacing unnamed captures, and confirming ASLR is active across deployments. The advisory also notes that underlying Ubuntu Server 20.04 LTS used by some affected versions has reached end of life, and recommends upgrading to newer supported Ubuntu releases or enabling Ubuntu Pro/ESM.

This is a vendor-disclosed vulnerability with no evidence of active exploitation. CISA republished the advisory as-is from Hitachi Energy PSIRT, reminding operators of energy-sector ICS to apply standard network segmentation and defense-in-depth practices given e-mesh EMS's worldwide deployment in critical infrastructure.

## Mentioned in this report

- Vulnerabilities: CVE-2026-42945

Source reporting: https://www.cisa.gov/news-events/ics-advisories/icsa-26-188-03

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