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

Summary

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.

Timeline

1. Oct 12, 2026, 8:59 PM UTCCVE published
2. Oct 13, 2026, 5:49 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: total

3. Oct 13, 2026, 5:50 PM UTCRecord last updated

Affected versions

• 0xJacky nginx-ui

  fixed in 2.4.1

• github.com/0xJacky/Nginx-UIGo

  fixed in 1.9.10-0.20260703131214-23d1934099b0

References 3