CVE-2026-84317: Nginx UI: MCP nginx_config_add skips config directive validation → authenticated nginx directive injection (RCE on the official image)

Vulnerability summary

CVE-2026-84317 is a high (CVSS 8.8) Improper Input Validation vulnerability in 0xjacky nginx-ui. EPSS estimates a 0.48% chance of exploitation in the next 30 days, higher than 41.2% of scored vulnerabilities.

Timeline

1. 12-10-2026
   PublishedVulnerability first disclosed.
2. 13-10-2026
   Last modifiedVulnerability information updated.

Description

Nginx UI is a web user interface for the Nginx web server. Prior to 2.4.1, internal/config/validation.go (ValidateConfigFile) is a security control that blocks dangerous nginx directives — js_*, perl_*, load_module of the njs/perl modules, and user root. It is enforced on three of the four config-write paths: api/config/add.go, api/config/modify.go, and mcp/config/config_modify.go. The fourth path — the MCP tool nginx_config_add (mcp/config/config_add.go) — does NOT call it: it writes the caller-supplied content straight to disk and reloads nginx. An authenticated MCP caller (or an MCP agent induced via prompt injection) can therefore inject exactly the directives the control is meant to block, leading to nginx code execution on deployments where the njs/perl module is available (e.g. the official Docker image). This issue is fixed in version 2.4.1.

• CWE-20Improper Input ValidationThe product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
• CWE-693Protection Mechanism FailureThe product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.