Symlink Attack in Echo Go with Api Keys

A symlink attack in the Echo Go ecosystem becomes particularly high-risk when API keys are involved because keys are often stored in predictable locations or passed via environment variables that a compromised handler can traverse. In Echo Go, route handlers commonly load keys from files or mounted secrets at startup, and if an attacker can trick the service into following a symbolic link during file operations (for example, when writing logs, rotating keys, or caching configuration), they may redirect those operations to a sensitive path. This combines path traversal via symlink with the presence of API keys, effectively exposing secrets through an otherwise benign file interaction.

Consider an Echo Go service that writes rotated key material to a directory without canonicalizing paths. If an attacker registers a symlink at the expected target location before the service rotates or writes keys, the write follows the symlink and overwrites a file the service trusts. Because the service uses those API keys for downstream authentication or signing, the attacker can replace valid keys with their own, leading to privilege escalation or service impersonation. The attack does not require authentication—Echo Go’s unauthenticated endpoints or misconfigured CORS can suffice to trigger the malicious file creation or overwrite. This maps to BFLA/Privilege Escalation and BOLA/IDOR checks in middleBrick’s scan, because the ability to manipulate file paths and gain access to key material represents a clear ownership and authorization boundary failure.

In the context of middleBrick’s 12 security checks, a symlink attack involving API keys would appear as a finding under BFLA/Privilege Escalation and Data Exposure, with risk tied to key leakage and unauthorized use. The scanner tests unauthenticated paths common in Echo Go services and looks for indications that file operations can be redirected. Because API keys often drive authorization, any exposure through insecure file handling has severe downstream impact, potentially compromising integrations and client applications that rely on those keys for outbound calls.

To mitigate symlink risks when handling API keys in Echo Go, ensure file operations use absolute paths and avoid user-controlled path segments. Always canonicalize file paths with filepath.EvalSymlinks before opening, writing, or rotating key files, and validate that the resolved path resides within an allowed directory. Do not rely on relative paths or environment-derived locations that an attacker can influence through symlinks.

Secure key loading with path validation

package main

import (
    "fmt"
    "io/ioutil"
    "os"
    "path/filepath"
)

const allowedDir = "/etc/echo-go/secrets/"

func loadAPIKey(filename string) ([]byte, error) {
    // Resolve symlinks and ensure the path stays within allowedDir
    requested := filepath.Join(allowedDir, filename)
    absRequested, err := filepath.Abs(requested)
    if err != nil {
        return nil, fmt.Errorf("invalid path: %w", err)
    }
    resolved, err := filepath.EvalSymlinks(absRequested)
    if err != nil {
        return nil, fmt.Errorf("failed to resolve symlinks: %w", err)
    }
    // Ensure the resolved path is still inside the allowed directory
    if !isSubpath(resolved, allowedDir) {
        return nil, fmt.Errorf("path escape detected: %s", resolved)
    }
    return ioutil.ReadFile(resolved)
}

func isSubpath(path, dir string) bool {
    rel, err := filepath.Rel(dir, path)
    return err == nil && rel != ".." && !startsWith(rel, "..\