Symlink Attack in Echo Go with Cockroachdb

A symlink attack in an Echo Go service that uses CockroachDB can occur when user-controlled data influences filesystem operations—such as file writes, exports, or backup routines—without proper path validation. If your Go handler saves uploaded filenames or constructs database dump paths using values from requests, an attacker can provide a filename like ../../../etc/passwd or a specially crafted name that traverses directories. Because CockroachDB is often used in distributed environments where backups, logs, or external file stores are written to shared or mounted volumes, a symlink can be placed in a location the application believes is safe, pointing to a sensitive system file or directory. When the application later writes to that path, it follows the symlink and alters the target, potentially overwriting critical data or injecting content into a location that CockroachDB or other processes read.

In the context of an API scanned by middleBrick, unchecked file operations triggered by API inputs appear as BFLA/Privilege Escalation and Unsafe Consumption findings. The scanner does not assume trust in the API surface; it tests whether exported endpoints allow path manipulation that can redirect file writes. Because CockroachDB clusters often rely on stable filesystem paths for logs, backups, and external storage integrations, a symlink placed on a mounted volume can redirect writes into the cluster’s operational space. This does not require authentication if the endpoint is unauthenticated or weakly guarded, aligning with middleBrick’s black-box testing methodology for unauthenticated attack surface coverage.

Real-world patterns include handlers that use os.Rename, os.Link, or backup scripts that construct target paths from request parameters. For example, an endpoint that accepts a backup_name query parameter and passes it to a shell command or file routine without sanitization can be coerced into writing to an unexpected location. middleBrick’s checks for Property Authorization and Input Validation highlight these risks by correlating spec definitions with runtime behavior, ensuring that path construction logic does not rely on unchecked user input.

To mitigate symlink risks in an Echo Go service interacting with CockroachDB, enforce strict path controls around any filesystem interaction and isolate database operations from user-supplied filenames. Use a combination of basename extraction, allowlist validation, and dedicated service accounts with minimal filesystem permissions. Avoid constructing filesystem paths from request data; if you must store files related to CockroachDB operations, generate deterministic names and store them in isolated directories.

Example 1: Safe backup filename handling

Ensure backup filenames are generated server-side and never directly reflect user input. If you accept a logical identifier, map it to a safe filename internally.

package main

import (
    "fmt"
    "net/http"
    "os"
    "path/filepath"

    "github.com/labstack/echo/v4"
)

func safeBackupHandler(c echo.Context) error {
    // Accept a logical identifier, not a raw filename
    instanceID := c.Param("instanceID")
    baseDir := "/srv/cockroach/backups"

    // Use a deterministic, server-generated name
    filename := fmt.Sprintf("backup-%s.sql", instanceID)
    target := filepath.Join(baseDir, filename)

    // Ensure the final path is within baseDir
    if resolved, err := filepath.EvalSymlinks(target); err == nil {
        dir := filepath.Dir(resolved)
        if dir != filepath.Clean(baseDir) {
            return c.String(http.StatusBadRequest, "invalid path")
        }
    }

    // Perform CockroachDB backup via CLI or client; example placeholder
    // err := runCockroachBackup(target)
    // if err != nil { ... }

    return c.JSON(http.StatusOK, map[string]string{"file": filename})
}

Example 2: Validating uploaded filenames before storage

If you must accept file uploads, sanitize the filename and avoid preserving directory components or extensions that could mask executable content.

package main

import (
    "io"
    "net/http"
    "os"
    "path/filepath"
    "strings"

    "github.com/labstack/echo/v4"
)

func uploadFileHandler(c echo.Context) error {
    file, err := c.FormFile("file")
    if err != nil {
        return c.String(http.StatusBadRequest, "missing file")
    }

    // Retain only the base name and allowlist extensions
    original := file.Filename
    ext := filepath.Ext(original)
    base := strings.TrimSuffix(original, ext)
    safeBase := filepath.Base(base) // removes any path components
    safeExt := filepath.Clean(ext)
    if safeExt == "" || (safeExt != ".sql" && safeExt != ".csv") {
        return c.String(http.StatusBadRequest, "extension not allowed")
    }

    filename := safeBase + safeExt
    target := filepath.Join("/srv/uploads", filename)

    // Ensure no symlink or traversal escapes the target directory
    if resolved, err := filepath.EvalSymlinks(target); err == nil {
        if !strings.HasPrefix(resolved, "/srv/uploads") {
            return c.String(http.StatusBadRequest, "path escape detected")
        }
    }

    src, err := file.Open()
    if err != nil {
        return c.String(http.StatusInternalServerError, "unable to open file")
    }
    defer src.Close()

    dst, err := os.Create(target)
    if err != nil {
        return c.String(http.StatusInternalServerError, "unable to create file")
    }
    defer dst.Close()

    if _, err = io.Copy(dst, src); err != nil {
        return c.String(http.StatusInternalServerError, "upload failed")
    }

    // Optionally trigger a CockroachDB import job using the safe path
    // err = runCockroachImport(target)
    // if err != nil { ... }

    return c.JSON(http.StatusOK, map[string]string{"stored": filename})
}

General operational safeguards

• Run CockroachDB processes under dedicated service accounts with read/write access only to required directories.
• Mount volumes used for backups or logs with options that disable symlink following where possible (e.g., nosymlink mount flags) or use isolated filesystems.
• Audit paths used in backup and export routines with tools like middleBrick to verify that no unchecked user input reaches filesystem operations.