Symlink Attack in Chi with Cockroachdb

A symlink attack in the context of a Chi-based service using CockroachDB occurs when an attacker manipulates file system references to redirect data access or backups to an unintended location. Chi is a lightweight routing library for Go, and when combined with CockroachDB, a distributed SQL database, the risk centers around insecure file operations, backup scripts, or log handling that reference user-controlled paths.

Consider a scenario where a Chi endpoint exposes a file download or backup feature that constructs file paths using user input without validating whether the resolved path is within an allowed directory. An attacker can provide a specially crafted filename containing a symbolic link (e.g., ../../../etc/backup) that traverses outside the intended directory. If the application uses CockroachDB to store metadata about backups or files, the attacker might trick the system into reading or writing database-related files (such as configuration or certificate files) via the symlink, potentially exposing credentials or enabling further compromise.

Because CockroachDB often relies on filesystem-backed storage and may involve file-based operations for backups, restores, or log collection, a symlink can redirect these operations. For example, a backup script invoked by a Chi handler might write a CockroachDB backup to a path derived from user input. If that path is a symlink to a sensitive location, the backup could overwrite critical files or expose sensitive data. The unauthenticated scanning capability of middleBrick can help detect such exposed endpoints by testing path traversal and symlink resolution behavior in the unauthenticated attack surface.

In this specific combination, the vulnerability arises not from CockroachDB itself but from how the application layer (Chi) handles file paths and references before interacting with the database. MiddleBrick’s checks for Path Traversal and File Disclosure can surface indicators of such misconfigurations, especially where backups or logs are involved.

To remediate symlink risks in a Chi application using CockroachDB, focus on secure path handling, input validation, and isolation of file operations. Below are concrete Go code examples demonstrating safe practices.

1. Validate and clean file paths

Always resolve and sanitize user-supplied paths. Use filepath.Clean and ensure the final path remains within a designated base directory.

import (
    "path/filepath"
    "net/http"
    "github.com/go-chi/chi/v5"
)

const baseBackupDir = "/safe/backup/dir"

func safeBackupHandler(w http.ResponseWriter, r *http.Request) {
    requestedFile := chi.URLParam(r, "file")
    // Clean the path to remove redundant separators and ".."
    cleanName := filepath.Clean(requestedFile)
    // Ensure the resolved path is inside the allowed directory
    finalPath := filepath.Join(baseBackupDir, cleanName)
    if !isSubpath(baseBackupDir, finalPath) {
        http.Error(w, "invalid path", http.StatusBadRequest)
        return
    }
    // Proceed with CockroachDB backup logic using finalPath
    w.Write([]byte("Backup initiated safely"))
}

func isSubpath(base, path string) bool {
    rel, err := filepath.Rel(base, path)
    return err == nil && !isDotDot(rel)
}

func isDotDot(path string) bool {
    return len(path) >= 3 && path[:3] == ".."
}

2. Avoid symlink-following during backup/restore

When invoking CockroachDB backup commands, ensure the target directory does not follow symlinks. Use absolute paths and verify the existence and type of each directory component.

import (
    "os"
    "os/exec"
)

func runCockroachBackup(destination string) error {
    // Ensure destination is an absolute path within an allowed root
    absDest, err := filepath.Abs(destination)
    if err != nil {
        return err
    }
    if !isUnderRoot(absDest, "/safe/backup/dir") {
        return fmt.Errorf("destination outside allowed directory")
    }
    // Ensure no symlink at the destination
    fi, err := os.Lstat(absDest)
    if err != nil && !os.IsNotExist(err) {
        return err
    }
    if fi != nil && fi.Mode()&os.ModeSymlink != 0 {
        return fmt.Errorf("destination is a symlink")
    }
    cmd := exec.Command("cockroach", "sql", "--execute", "BACKUP DATABASE mydb TO "+absDest)
    return cmd.Run()
}

func isUnderRoot(path, root string) bool {
    rel, err := filepath.Rel(root, path)
    return err == nil && !isDotDot(rel)
}

3. Secure log and metadata handling

If your Chi service logs request paths or stores metadata in CockroachDB, avoid storing or using raw user input in file system operations. Use database identifiers instead of file paths when possible.

import (
    "database/sql"
    _ "github.com/cockroachdb/cockroach-go/v2/crdb"
)

func logBackupAttempt(db *sql.DB, userID string) error {
    _, err := db.Exec(`INSERT INTO backup_logs (user_id, status) VALUES ($1, $2)`, userID, "initiated")
    return err
}

By combining strict path validation, symlink checks, and secure logging, you reduce the attack surface for symlink-based threats in a Chi and CockroachDB environment.