Sanitize user input in execInContainer to prevent injection (#305)

* security: sanitize user input in execInContainer

This change implements command injection protection for the 'vm exec' command
by adding a command whitelist and robust shell argument escaping.

Changes:
- Added `escapeShellArg` utility in `pkg/container/linuxkit.go` to safely quote
  arguments for the remote shell.
- Updated `LinuxKitManager.Exec` to escape all command arguments before
  passing them to SSH.
- Implemented `allowedExecCommands` whitelist in `internal/cmd/vm/cmd_container.go`.
- Added i18n support for new security-related error messages.
- Added unit tests for escaping logic and whitelist validation.

Fixes findings from OWASP Top 10 Security Audit (PR #205).

* security: sanitize user input in execInContainer

This change implements command injection protection for the 'vm exec' command
by adding a command whitelist and robust shell argument escaping.

Changes:
- Added `escapeShellArg` utility in `pkg/container/linuxkit.go` to safely quote
  arguments for the remote shell.
- Updated `LinuxKitManager.Exec` to escape all command arguments before
  passing them to SSH.
- Implemented `allowedExecCommands` whitelist in `internal/cmd/vm/cmd_container.go`.
- Added i18n support for new security-related error messages.
- Added unit tests for escaping logic and whitelist validation.
- Fixed minor formatting issue in `pkg/io/local/client.go`.

Fixes findings from OWASP Top 10 Security Audit (PR #205).

* security: sanitize user input in execInContainer

This change implements command injection protection for the 'vm exec' command
by adding a command whitelist and robust shell argument escaping.

Changes:
- Added `escapeShellArg` utility in `pkg/container/linuxkit.go` to safely quote
  arguments for the remote shell (mitigates SSH command injection).
- Updated `LinuxKitManager.Exec` to escape all command arguments.
- Implemented `allowedExecCommands` whitelist in `internal/cmd/vm/cmd_container.go`.
- Added i18n support for new security-related error messages in `en_GB.json`.
- Added unit tests for escaping logic and whitelist validation.
- Fixed a minor pre-existing formatting issue in `pkg/io/local/client.go`.

Note: The 'merge / auto-merge' CI failure was identified as an external
reusable workflow issue (missing repository context for the 'gh' CLI), and
has been left unchanged to maintain PR scope and security policies.

Fixes findings from OWASP Top 10 Security Audit (PR #205).

internal/cmd/vm/cmd_container.go

@@ -16,6 +16,34 @@ import (
 	"github.com/spf13/cobra"
 )
 
+var (
+	// allowedExecCommands is a whitelist of commands allowed to be executed in containers.
+	allowedExecCommands = map[string]bool{
+		"ls":       true,
+		"ps":       true,
+		"cat":      true,
+		"top":      true,
+		"df":       true,
+		"du":       true,
+		"ifconfig": true,
+		"ip":       true,
+		"ping":     true,
+		"netstat":  true,
+		"date":     true,
+		"uptime":   true,
+		"whoami":   true,
+		"id":       true,
+		"uname":    true,
+		"echo":     true,
+		"tail":     true,
+		"head":     true,
+		"grep":     true,
+		"sleep":    true,
+		"sh":       true,
+		"bash":     true,
+	}
+)
+
 var (
 	runName         string
 	runDetach       bool
@@ -330,6 +358,16 @@ func addVMExecCommand(parent *cobra.Command) {
 }
 
 func execInContainer(id string, cmd []string) error {
+	if len(cmd) == 0 {
+		return errors.New(i18n.T("cmd.vm.error.id_and_cmd_required"))
+	}
+
+	// Validate against whitelist
+	baseCmd := cmd[0]
+	if !allowedExecCommands[baseCmd] {
+		return errors.New(i18n.T("cmd.vm.error.command_not_allowed", map[string]interface{}{"Command": baseCmd}))
+	}
+
 	manager, err := container.NewLinuxKitManager(io.Local)
 	if err != nil {
 		return fmt.Errorf(i18n.T("i18n.fail.init", "container manager")+": %w", err)

internal/cmd/vm/cmd_container_test.go

@@ -0,0 +1,51 @@
+package vm
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestExecInContainer_Whitelist(t *testing.T) {
+	tests := []struct {
+		name     string
+		cmd      []string
+		expected string // Expected error substring
+	}{
+		{
+			"Allowed command",
+			[]string{"ls", "-la"},
+			"", // Will fail later with "failed to determine state path" or similar, but NOT whitelist error
+		},
+		{
+			"Disallowed command",
+			[]string{"rm", "-rf", "/"},
+			"command not allowed: rm",
+		},
+		{
+			"Injection attempt in first arg",
+			[]string{"ls; rm", "-rf", "/"},
+			"command not allowed: ls; rm",
+		},
+		{
+			"Empty command",
+			[]string{},
+			"container ID and command required",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := execInContainer("test-id", tt.cmd)
+			if tt.expected == "" {
+				// Should NOT be a whitelist error
+				if err != nil {
+					assert.NotContains(t, err.Error(), "command not allowed")
+				}
+			} else {
+				assert.Error(t, err)
+				assert.Contains(t, err.Error(), tt.expected)
+			}
+		})
+	}
+}

pkg/container/exec_security_test.go

@@ -0,0 +1,28 @@
+package container
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestEscapeShellArg(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{"ls", "'ls'"},
+		{"foo bar", "'foo bar'"},
+		{"it's", "'it'\\''s'"},
+		{"; rm -rf /", "'; rm -rf /'"},
+		{"$(whoami)", "'$(whoami)'"},
+		{"`whoami`", "'`whoami`'"},
+		{"\"quoted\"", "'\"quoted\"'"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			assert.Equal(t, tt.expected, escapeShellArg(tt.input))
+		})
+	}
+}

pkg/container/linuxkit.go

@@ -7,6 +7,7 @@ import (
 	goio "io"
 	"os"
 	"os/exec"
+	"strings"
 	"syscall"
 	"time"
 
@@ -416,6 +417,13 @@ func (f *followReader) Close() error {
 	return f.file.Close()
 }
 
+// escapeShellArg safely quotes a string for use as a shell argument.
+func escapeShellArg(arg string) string {
+	// Wrap in single quotes and escape existing single quotes.
+	// For example: 'it'\''s'
+	return "'" + strings.ReplaceAll(arg, "'", "'\\''") + "'"
+}
+
 // Exec executes a command inside the container via SSH.
 func (m *LinuxKitManager) Exec(ctx context.Context, id string, cmd []string) error {
 	if err := ctx.Err(); err != nil {
@@ -441,7 +449,11 @@ func (m *LinuxKitManager) Exec(ctx context.Context, id string, cmd []string) err
 		"-o", "LogLevel=ERROR",
 		"root@localhost",
 	}
-	sshArgs = append(sshArgs, cmd...)
+
+	// Escape each command argument for the remote shell
+	for _, c := range cmd {
+		sshArgs = append(sshArgs, escapeShellArg(c))
+	}
 
 	sshCmd := exec.CommandContext(ctx, "ssh", sshArgs...)
 	sshCmd.Stdin = os.Stdin

pkg/i18n/locales/en_GB.json

@@ -633,6 +633,8 @@
 			"stop.short": "Stop a running VM",
 			"logs.short": "View VM logs",
 			"exec.short": "Execute a command in a VM",
+			"error.id_and_cmd_required": "container ID and command required",
+			"error.command_not_allowed": "command not allowed: {{.Command}}",
 			"templates.short": "Manage LinuxKit templates"
 		},
 		"monitor": {