Symlink Attack in Buffalo with Cockroachdb

A symlink attack in a Buffalo application using CockroachDB typically occurs when file system operations are influenced by attacker-controlled data that ultimately affects how or where files are stored. If a Buffalo handler constructs file paths using user input and passes that input to functions that resolve symbolic links or create files, an attacker may be able to point a symlink to a sensitive location such as a CockroachDB node configuration file, a certificate, or a data directory used by an auxiliary service.

Buffalo encourages rapid development and often integrates with external services like CockroachDB for persistent storage. When developers use user-supplied filenames or paths to store uploaded files, export database dumps, or write logs, they must ensure those paths are isolated from filesystem traversal and symlink manipulation. If an uploaded file is written to a directory that is later read by a CockroachDB sidecar, backup script, or monitoring tool, a symlink can redirect writes to a critical system path. This can lead to data corruption, unauthorized configuration changes, or information disclosure involving CockroachDB credentials stored in files or environment variables referenced by the application.

The attack surface is expanded when the Buffalo app runs with elevated privileges or when file system operations are not confined to a dedicated, non-privileged directory. Because CockroachDB is often run as a separate process, a symlink that redirects a log or data file into the CockroachDB data directory can interfere with startup or encryption procedures. Although middleBrick focuses on detection and reporting rather than remediation, recognizing these patterns helps developers understand why input validation and strict path handling are essential when integrating file system operations with database services.

To mitigate symlink risks in a Buffalo application that interacts with CockroachDB, enforce strict path controls and avoid direct use of user input in filesystem operations. Always resolve paths against a controlled base directory and avoid symbolic link resolution when writing or reading files tied to database operations.

1. Use a dedicated upload directory with cleaned base paths

Ensure uploaded files are saved under a known directory, and use filepath.Clean to remove traversal elements. Do not preserve original filenames without validation.

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

    "github.com/gobuffalo/buffalo"
)

func uploadHandler(c buffalo.Context) error {
    file, err := c.FormFile("file")
    if err != nil {
        return c.Render(400, r.Text("file missing"))
    }

    // Define a fixed upload directory outside of web root
    uploadDir := "/var/app/uploads"
    cleanDir := filepath.Clean(uploadDir)

    // Clean the filename and reject paths containing separators
    originalName := filepath.Base(file.Filename)
    if originalName == "." || filepath.IsAbs(originalName) {
        return c.Render(400, r.Text("invalid filename"))
    }

    dest := filepath.Join(cleanDir, originalName)
    // Ensure the final path remains inside the upload directory
    if rel, err := filepath.Rel(cleanDir, dest); err != nil || rel == ".." {
        return c.Render(400, r.Text("invalid path"))
    }

    f, err := os.OpenFile(dest, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0600)
    if err != nil {
        return c.Render(500, r.Text("unable to save file"))
    }
    defer f.Close()

    // file.Copy or io.Copy logic here
    return c.Render(200, r.JSON(&map[string]string{"path": dest}))
}

2. Avoid symlink resolution when accessing CockroachDB-related files

If your app reads configuration or certificate files that may be referenced by CockroachDB, disable symlink following to prevent redirection to malicious locations.

import (
    "os"
    "path/filepath"
)

func readConfigNoSymlink(base, file string) ([]byte, error) {
    // Clean and join without evaluating symlinks
    dir := filepath.Clean(base)
    name := filepath.Clean(file)
    full := filepath.Join(dir, name)

    // Ensure the resolved path remains within base
    if rel, err := filepath.Rel(dir, full); err != nil || rel == ".." || filepath.IsAbs(rel) {
        return nil, os.ErrNotExist
    }

    // Use os.OpenFile with O_NOFOLLOW where supported (Go 1.18+)
    f, err := os.OpenFile(full, os.O_RDONLY, 0)
    if err != nil {
        return nil, err
    }
    defer f.Close()

    return os.ReadFile(f.Name())
}

3. Isolate CockroachDB auxiliary files

If your Buffalo app generates backups, logs, or scripts that interact with CockroachDB, store them in directories with strict permissions and without symlink targets that could be influenced by web-accessible inputs. Consider using environment variables for paths rather than deriving them from user data.

import (
    "os"
)

func cockroachDataPath() string {
    base := os.Getenv("COCKROACH_DATA_DIR")
    if base == "" {
        base = "/var/lib/cockroach"
    }
    return filepath.Clean(base)
}