Nginx Configuration Directory Vulnerable to Recursive Deletion via Improper Path Validation

Summary

The nginx-ui configuration improperly handles URL-encoded traversal sequences. When specially crafted paths are supplied, the backend resolves them to the base Nginx configuration directory and executes the operation on the base directory (/etc/nginx). In particular, this allows an authenticated user to remove the entire /etc/nginx directory, resulting in a partial Denial of Service.

Details

The file deletion logic fails to correctly validate and normalize paths containing URL-encoded traversal sequences such as ..%252F.

When such input is processed, the internal path resolution logic attempts to clamp the path into the allowed configuration directory. Instead of rejecting the traversal attempt, the clamping mechanism resolves the path to the base Nginx configuration directory itself.

Because the deletion handler invokes os.RemoveAll, which recursively removes directories, this results in the deletion of the entire /etc/nginx directory.

This behavior creates a dangerous interaction between path normalization and deletion logic:

• Traversal sequences are not rejected.
• Double-encoding (..%252F) is used to bypass initial shallow filters.
• The clamping mechanism resolves malicious paths to the base configuration directory.
• The deletion handler recursively deletes the resolved path.

As a result, an attacker can trigger deletion of the entire Nginx configuration directory instead of being blocked by path validation logic.

Root Cause

The vulnerability results from a combination of design flaws:

• Improper Path Canonicalization: URL-encoded traversal sequences are not properly rejected.
• Unsafe Fallback Logic: The GetConfPath clamping mechanism returns the base configuration directory when traversal is detected instead of rejecting the request.
• Unsafe Deletion Primitive: The deletion handler invokes os.RemoveAll, which recursively deletes directories without additional safeguards. (delete.go)

	// Delete the file or directory
	err = os.RemoveAll(fullPath)
	if err != nil {
		cosy.ErrHandler(c, err)
		return
	}

This interaction causes the deletion operation to target the most sensitive directory when a traversal attempt occurs.

Environment

• Server OS: Kali Linux 6.17.10-1kali1 (6.17.10+kali-amd64)
• Nginx UI Version: nginx-ui v2.3.3