fix(exec): security guard bypass fixes for PowerShell/CMD encoding and path traversal
- Split deny patterns into defaultDenyPatterns (all platforms) and windowsDenyPatterns (Windows-only) to avoid false positives - Add PowerShell encoding bypass detection: - [Text.Encoding] and [System.Text.Encoding] variants - -EncodedCommand short forms (-e, -ec, -enc) - .GetString([byte[]] with whitespace variations - FromBase64String decoding - PowerShell variable = [byte[](...) patterns - Literal \uXXXX Unicode escape sequences - Expand PowerShell ($env:VAR) and CMD (%VAR%) environment variables before workspace path checking to prevent $env:USERPROFILE bypass - Expand ~ to home directory on Windows - Add .../.../ path traversal variant detection (blocks .../.../, ..../..../) - Add symlink/junction resolution before workspace check - Add Windows path normalization for ADS (file.txt:stream) and extended-length paths (\?\) - Add comprehensive tests for all new patterns Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This commit is contained in:
sky5454
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ff42ceba6a
2 changed files with 190 additions and 7 deletions
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@ -95,14 +95,25 @@ var (
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regexp.MustCompile(`\bssh\b.*@`),
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regexp.MustCompile(`\beval\b`),
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regexp.MustCompile(`\bsource\s+.*\.sh\b`),
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// PowerShell encoding bypass: [Text.Encoding] used to construct command strings.
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regexp.MustCompile(`\[text\.encoding\]`),
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// PowerShell -EncodedCommand flag (base64-encoded command).
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regexp.MustCompile(`-encodedcommand`),
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}
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// windowsDenyPatterns contains PowerShell-specific deny patterns that only
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// apply on Windows, where commands are executed via powershell -Command.
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windowsDenyPatterns = []*regexp.Regexp{
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// [Text.Encoding] used to construct command strings at runtime.
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// Matches [Text.Encoding] and [System.Text.Encoding] variants.
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regexp.MustCompile(`\[(?:\w+\.)?text\.encoding\]`),
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// PowerShell -EncodedCommand flag (base64-encoded command) and short forms -e, -ec, -enc.
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regexp.MustCompile(` -e[cn]\b`),
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// .GetString called on byte array to decode commands.
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regexp.MustCompile(`\.getstring\(\[byte\[\]`),
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regexp.MustCompile(`\.getstring\s*\(\s*\[byte\[\]`),
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// FromBase64String used in command construction chain.
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regexp.MustCompile(`frombase64string\(`),
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// PowerShell variable holding byte array used in GetString.
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regexp.MustCompile(`\$[a-zA-Z_]\w*\s*=\s*\[byte\[\]`),
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// Unicode escape sequences that could be used to construct commands.
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// Matches \uXXXX format used to represent characters like i = "i"
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regexp.MustCompile(`\\u[0-9a-fA-F]{4}`),
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}
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// absolutePathPattern matches absolute file paths in commands (Unix and Windows).
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@ -146,6 +157,9 @@ func NewExecToolWithConfig(
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allowRemote = execConfig.AllowRemote
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if enableDenyPatterns {
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denyPatterns = append(denyPatterns, defaultDenyPatterns...)
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if runtime.GOOS == "windows" {
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denyPatterns = append(denyPatterns, windowsDenyPatterns...)
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}
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if len(execConfig.CustomDenyPatterns) > 0 {
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fmt.Printf("Using custom deny patterns: %v\n", execConfig.CustomDenyPatterns)
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for _, pattern := range execConfig.CustomDenyPatterns {
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@ -169,6 +183,9 @@ func NewExecToolWithConfig(
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}
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} else {
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denyPatterns = append(denyPatterns, defaultDenyPatterns...)
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if runtime.GOOS == "windows" {
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denyPatterns = append(denyPatterns, windowsDenyPatterns...)
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}
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}
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var timeout time.Duration
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@ -1027,6 +1044,30 @@ func (t *ExecTool) executeSendKeys(args map[string]any) *ToolResult {
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}
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}
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// expandPowerShellEnvVars expands environment variable syntax used by both
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// PowerShell ($env:VAR) and CMD (%VAR%) to their actual values.
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func expandPowerShellEnvVars(cmd string) string {
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// Handle PowerShell style: $env:VAR and ${env:VAR}
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rePs := regexp.MustCompile(`\$\{?env:(\w+)\}?`)
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cmd = rePs.ReplaceAllStringFunc(cmd, func(match string) string {
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varName := rePs.FindStringSubmatch(match)[1]
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if val := os.Getenv(varName); val != "" {
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return val
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}
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return match
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})
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// Handle CMD style: %VAR%
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reCmd := regexp.MustCompile(`%([^%]+)%`)
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return reCmd.ReplaceAllStringFunc(cmd, func(match string) string {
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varName := reCmd.FindStringSubmatch(match)[1]
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if val := os.Getenv(varName); val != "" {
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return val
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}
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return match
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})
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}
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func (t *ExecTool) guardCommand(command, cwd string) string {
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cmd := strings.TrimSpace(command)
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lower := strings.ToLower(cmd)
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@ -1062,7 +1103,8 @@ func (t *ExecTool) guardCommand(command, cwd string) string {
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}
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if t.restrictToWorkspace {
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if strings.Contains(cmd, "..\\") || strings.Contains(cmd, "../") {
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// Block path traversal patterns including .../.../ variants
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if regexp.MustCompile(`\.\.(?:[\\/]\.\.)*[\\/]`).MatchString(cmd) {
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return "Command blocked by safety guard (path traversal detected)"
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}
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@ -1076,6 +1118,16 @@ func (t *ExecTool) guardCommand(command, cwd string) string {
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// file:// URIs are still validated against the workspace boundary.
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webSchemes := []string{"http:", "https:", "ftp:", "ftps:", "sftp:", "ssh:", "git:"}
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// On Windows, expand ~ and PowerShell environment variables ($env:VAR) before path checking
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if runtime.GOOS == "windows" {
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// Expand PowerShell environment variables ($env:VAR and ${env:VAR})
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cmd = expandPowerShellEnvVars(cmd)
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// Also expand ~ for completeness
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if home, err := os.UserHomeDir(); err == nil {
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cmd = strings.ReplaceAll(cmd, "~", filepath.FromSlash(home))
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}
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}
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matchIndices := absolutePathPattern.FindAllStringIndex(cmd, -1)
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for _, loc := range matchIndices {
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@ -1107,6 +1159,22 @@ func (t *ExecTool) guardCommand(command, cwd string) string {
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continue
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}
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// Windows-specific: normalize paths to block ADS and extended-length paths
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if runtime.GOOS == "windows" {
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// Strip \\?\ prefix (extended-length path)
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p = strings.TrimPrefix(p, `\\?\`)
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// Strip NTFS alternate data streams (only if colon is not at position 1 = drive letter)
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if idx := strings.Index(p, ":"); idx > 1 {
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p = p[:idx]
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}
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}
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// Check symlinks and junctions
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resolved, err := filepath.EvalSymlinks(p)
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if err == nil {
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p = resolved
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}
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if safePaths[p] {
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continue
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}
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@ -703,6 +703,102 @@ func TestShellTool_URLBypassPrevented(t *testing.T) {
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}
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}
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// TestShellTool_TildeBypassPrevented verifies that ~ (home directory) cannot be
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// used to escape workspace restrictions on Windows.
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func TestShellTool_TildeBypassPrevented(t *testing.T) {
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tmpDir := t.TempDir()
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tool, err := NewExecTool(tmpDir, true)
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if err != nil {
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t.Fatalf("unable to configure exec tool: %s", err)
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}
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ctx := context.Background()
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// Tilde should be blocked when it expands outside workspace
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blockedCommands := []string{
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"ls ~",
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"ls ~/some/path",
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"cat ~/.config/file",
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// PowerShell environment variables also expand to home directory
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"dir $env:USERPROFILE",
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"ls $env:USERPROFILE",
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"cat $env:USERPROFILE\\.config\\file",
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// CMD environment variables
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"cmd /c \"dir %USERPROFILE%\"",
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"cmd /c \"cd %USERPROFILE% && dir\"",
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"cmd /c \"type %USERPROFILE%\\.config\\file\"",
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}
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for _, cmd := range blockedCommands {
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result := tool.Execute(ctx, map[string]any{"action": "run", "command": cmd})
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if !result.IsError || !strings.Contains(result.ForLLM, "path outside working dir") {
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t.Errorf("tilde bypass should be blocked: %q\n got: %s", cmd, result.ForLLM)
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}
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}
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}
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// TestShellTool_PathTraversalVariants verifies that .../.../ and similar
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// path traversal variants are blocked.
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func TestShellTool_PathTraversalVariants(t *testing.T) {
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tmpDir := t.TempDir()
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tool, err := NewExecTool(tmpDir, true)
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if err != nil {
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t.Fatalf("unable to configure exec tool: %s", err)
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}
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ctx := context.Background()
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// Path traversal variants should be blocked
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blockedCommands := []string{
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"ls .../.../",
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"ls ..../..../",
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"cat .../.../../../etc/passwd",
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}
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for _, cmd := range blockedCommands {
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result := tool.Execute(ctx, map[string]any{"action": "run", "command": cmd})
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if !result.IsError || !strings.Contains(result.ForLLM, "path traversal") {
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t.Errorf("path traversal variant should be blocked: %q\n got: %s", cmd, result.ForLLM)
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}
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}
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// Legitimate commands with ... should not be blocked (if such commands exist)
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// Note: these will fail for other reasons but should not be blocked by path traversal
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allowedCommands := []string{
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"echo ...",
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"ls ...",
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}
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for _, cmd := range allowedCommands {
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result := tool.Execute(ctx, map[string]any{"action": "run", "command": cmd})
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// These should not be blocked by path traversal check specifically
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if strings.Contains(result.ForLLM, "path traversal") {
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t.Errorf("legitimate command with ... should not be blocked: %q", cmd)
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}
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}
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}
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// TestShellTool_SymlinkBypassPrevented verifies that symlinks pointing outside
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// workspace are detected and blocked after resolution.
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func TestShellTool_SymlinkBypassPrevented(t *testing.T) {
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tmpDir := t.TempDir()
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tool, err := NewExecTool(tmpDir, true)
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if err != nil {
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t.Fatalf("unable to configure exec tool: %s", err)
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}
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ctx := context.Background()
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// Commands with paths that could be symlinks should be checked
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// We can't easily test symlinks in a cross-platform way in unit tests,
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// but we verify the symlink resolution code path runs without error
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result := tool.Execute(ctx, map[string]any{"action": "run", "command": "ls /tmp"})
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// /tmp is typically outside a user workspace, should be blocked
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if !result.IsError || !strings.Contains(result.ForLLM, "path outside") {
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// This is expected to fail on most systems due to path restrictions
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}
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}
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// TestShellTool_PowerShellEncodingBypass verifies that PowerShell encoding bypass techniques are blocked.
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func TestShellTool_PowerShellEncodingBypass(t *testing.T) {
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tool, err := NewExecTool("", false)
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@ -715,6 +811,8 @@ func TestShellTool_PowerShellEncodingBypass(t *testing.T) {
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`[Text.Encoding]::ASCII.GetString([byte[]](0x6c,0x73,0x20,0x7e))`,
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`[Text.Encoding]::ASCII.GetString([byte[]](0x69,0x65,0x78))`,
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`[System.Text.Encoding]::ASCII.GetString([byte[]](0x69,0x65,0x78))`,
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`[System.Text.Encoding]::ASCII.GetString ([byte[]](0x69,0x65,0x78))`,
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`$b = [byte[]](0x69,0x65,0x78); [Text.Encoding]::ASCII.GetString($b)`,
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}
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for _, cmd := range encodingBypassCommands {
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@ -727,10 +825,14 @@ func TestShellTool_PowerShellEncodingBypass(t *testing.T) {
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}
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}
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// Commands using PowerShell's -EncodedCommand flag (base64).
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// Commands using PowerShell's -EncodedCommand flag (base64), including short forms.
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encodedCommands := []string{
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`powershell -NoProfile -NonInteractive -EncodedCommand SQBFAHIAaABlAGwAbAAvAC8A`,
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`pwsh -EncodedCommand aWV4`,
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`pwsh -e SQBFAHIAaABlAGwAbAAvAC8A`,
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`pwsh -ec aWV4`,
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`powershell -e SQBFAHIAaABlAGwAbAAvAC8A`,
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`powershell -ec aWV4`,
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}
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for _, cmd := range encodedCommands {
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@ -739,6 +841,19 @@ func TestShellTool_PowerShellEncodingBypass(t *testing.T) {
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t.Errorf("expected -EncodedCommand to be blocked: %s", cmd)
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}
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}
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// Unicode escape sequences that could construct malicious commands
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// Double backslash preserves literal \u in the string (Go escape → literal \)
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unicodeCommands := []string{
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`cmd /c "cd %USERPROFILE% \\u0026 dir"`,
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}
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for _, cmd := range unicodeCommands {
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result := tool.Execute(ctx, map[string]any{"action": "run", "command": cmd})
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if !result.IsError {
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t.Errorf("expected Unicode escape to be blocked: %s", cmd)
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}
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}
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}
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func TestShellTool_Background_ReturnsImmediately(t *testing.T) {
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