fix!: harden the vault against injection, silent data loss, and weak keys

README.md

@@ -15,6 +15,23 @@ A flexible Go library for secure secret management with multiple backend provide
 - **Thread Safe**: Concurrent access protection with read/write mutexes
 - **Comprehensive API**: Full CRUD operations plus metadata and existence checks
 
+## Upgrading to v0.3.0
+
+v0.3.0 is a security and correctness release. It contains breaking changes, each
+of which replaces behaviour that failed silently:
+
+| Change | Why | What to do |
+|---|---|---|
+| `Provider.Metadata()` returns `(Metadata, error)` | Every failure previously returned an empty struct, so a broken command, a timeout and "not configured" were indistinguishable | Handle the new error |
+| External configs referencing `{{value}}`/`{{password}}` in a `cmd` are rejected | The value was interpolated into a shell command with no quoting — a command-injection sink that also corrupted ordinary passwords | Move the secret to an `InputTemplate` (stdin) |
+| An existing but zero-length vault file is an error | It was read as "no vault here", so the constructor initialized and immediately overwrote it, destroying every secret | Restore from backup, or delete the file to start fresh |
+| Operations on a closed vault return `ErrVaultClosed` | They dereferenced nil state and panicked | Nothing, unless you relied on the panic |
+| Vault IDs are charset-validated | An ID is interpolated into a filename, and `filepath.Clean` *resolves* traversal rather than sanitizing it | Use IDs matching `^[a-zA-Z0-9][a-zA-Z0-9-_.]*$` |
+| Encryption keys must be exactly 32 bytes | `aes.NewCipher` also accepts 16 and 24, silently downgrading an "AES256" vault to AES-128/192 | Regenerate short keys |
+| `DeriveKey` returns a parameter-tagged salt | Changing the scrypt cost would otherwise silently change every derived key | Pass the returned salt back verbatim rather than base64-decoding it first |
+
+Local vault files written by earlier versions are read without migration.
+
 ## Quick Start
 
 ```go
@@ -63,7 +80,7 @@ Stores secrets in an AES-256 encrypted file with configurable key sources.
 ```go
 provider, _, err := vault.New("my-vault",
     vault.WithProvider(vault.ProviderTypeAES256),
-    vault.WithAESPath("~/secrets.vault"),
+    vault.WithAESPath("~/.config/flow/vaults"), // a directory, not a file
 )
 ```
 
@@ -79,7 +96,7 @@ Uses the [age encryption tool](https://age-encryption.org/) with public key cryp
 ```go
 provider, _, err := vault.New("my-vault", 
     vault.WithProvider(vault.ProviderTypeAge),
-    vault.WithAgePath("~/secrets.age"),
+    vault.WithAgePath("~/.config/flow/vaults"), // a directory, not a file
 )
 ```
 
@@ -107,7 +124,7 @@ Stores secrets in plain text JSON files.
 ```go
 provider, _, err := vault.New("my-vault",
     vault.WithProvider(vault.ProviderTypeUnencrypted), 
-    vault.WithUnencryptedPath("~/dev-secrets.json"),
+    vault.WithUnencryptedPath("~/.config/flow/vaults"), // a directory, not a file
 )
 ```
 
@@ -122,10 +139,12 @@ config := &vault.Config{
     Type: vault.ProviderTypeExternal,
     External: &vault.ExternalConfig{
         Get: vault.CommandConfig{
-            CommandTemplate: "bw get password {{key}}",
+            CommandTemplate: "bw get password '{{key}}'",
         },
         Set: vault.CommandConfig{
-            CommandTemplate: "bw create item --name {{key}} --password {{value}}",
+            CommandTemplate: "bw create item",
+            // The secret is piped to the command's stdin, never placed in it.
+            InputTemplate: "{{value}}",
         },
         // ... other operations
     },
@@ -134,6 +153,14 @@ config := &vault.Config{
 provider, err := vault.NewExternalVaultProvider(config)
 ```
 
+> **The secret value is not available to command templates.** A rendered command
+> is parsed and run by a shell and the template engine does no quoting, so
+> interpolating a secret there is a command-injection sink and silently corrupts
+> any value containing shell metacharacters (`p@$$w0rd` has `$$` replaced by the
+> process ID; `correct horse battery` word-splits to `correct`). Configurations
+> referencing `{{value}}` or `{{password}}` in a `cmd` are rejected at load —
+> use an `InputTemplate` instead.
+
 **External Provider Examples**
 
 Ready-to-use configurations for popular CLI tools are available in the [`examples/`](./examples/) directory:
@@ -165,7 +192,7 @@ secrets, _ := provider.ListSecrets()
 exists, _ := provider.HasSecret("api-key")
 
 // Get vault metadata
-metadata := provider.Metadata()
+metadata, err := provider.Metadata()
 ```
 
 ### Configuration from File

aes.go

@@ -1,10 +1,8 @@
 package vault
 
 import (
-	"errors"
 	"fmt"
-	"os"
-	"path/filepath"
+	"sort"
 	"sync"
 	"time"
 
@@ -22,7 +20,10 @@ const (
 type AESState struct {
 	Metadata `yaml:"metadata"`
 
-	Version int               `json:"version"`
+	// yaml, not json: this struct is marshaled with gopkg.in/yaml.v3, which
+	// ignores json tags and would otherwise have keyed this field as "version"
+	// only by lowercasing coincidence.
+	Version int               `yaml:"version"`
 	ID      string            `yaml:"id"`
 	Secrets map[string]string `yaml:"secrets"`
 }
@@ -43,13 +44,22 @@ func GenerateEncryptionKey() (string, error) {
 	return crypto.GenerateKey()
 }
 
-// DeriveEncryptionKey derives an AES encryption key from a passphrase
+// DeriveEncryptionKey derives an AES encryption key from a passphrase.
+//
+// An empty sal requests a freshly generated salt. Pass the returned salt back
+// verbatim to re-derive the same key; it carries the parameters it was made
+// with, so future changes to the defaults cannot alter an existing key.
 func DeriveEncryptionKey(passphrase, sal string) (string, string, error) {
-	key, salt, err := crypto.DeriveKey([]byte(passphrase), []byte(sal))
+	var salt []byte
+	if sal != "" {
+		salt = []byte(sal)
+	}
+
+	key, salt2, err := crypto.DeriveKey([]byte(passphrase), salt)
 	if err != nil {
 		return "", "", fmt.Errorf("failed to derive encryption key: %w", err)
 	}
-	return key, salt, nil
+	return key, salt2, nil
 }
 
 // ValidateEncryptionKey checks if a key is valid by attempting to encrypt/decrypt test data
@@ -77,10 +87,14 @@ func NewAES256Vault(cfg *Config) (*AES256Vault, error) {
 		return nil, fmt.Errorf("AES configuration is required")
 	}
 
-	path := filepath.Join(
-		filepath.Clean(cfg.Aes.StoragePath),
-		filepath.Clean(fmt.Sprintf("%s-%s.%s", vaultFileBase, cfg.ID, aesVaultFileExt)),
-	)
+	if err := cfg.Validate(); err != nil {
+		return nil, err
+	}
+
+	path, err := resolveVaultPath(cfg.Aes.StoragePath, cfg.ID, aesVaultFileExt)
+	if err != nil {
+		return nil, err
+	}
 
 	vault := &AES256Vault{
 		id:       cfg.ID,
@@ -119,20 +133,16 @@ func (v *AES256Vault) init() error {
 		Secrets: make(map[string]string),
 	}
 
-	return v.save()
+	return withVaultLock(v.fullPath, v.save)
 }
 
 // load retrieves the AESState from the vault file, decrypts it, and unmarshals it into an AESState struct.
 func (v *AES256Vault) load() error {
-	data, err := os.ReadFile(filepath.Clean(v.fullPath))
+	data, exists, err := readVaultFile(v.fullPath)
 	if err != nil {
-		if errors.Is(err, os.ErrNotExist) {
-			return nil
-		}
-		return fmt.Errorf("%w: failed to read vault file %s: %w", ErrVaultNotFound, v.fullPath, err)
+		return err
 	}
-
-	if len(data) == 0 {
+	if !exists {
 		return nil
 	}
 
@@ -147,14 +157,18 @@ func (v *AES256Vault) load() error {
 	if err := yaml.Unmarshal([]byte(dataStr), &state); err != nil {
 		return fmt.Errorf("failed to unmarshal vault state: %w", err)
 	}
+	if err := checkVaultVersion(state.Version, aesCurrentVaultVersion, v.fullPath); err != nil {
+		return err
+	}
+
 	v.state = &state
 	return nil
 }
 
 // save encrypts and writes the vault contents to disk
 func (v *AES256Vault) save() error {
 	if v.state == nil {
-		return nil
+		return ErrVaultClosed
 	}
 
 	if v.dek == "" {
@@ -171,41 +185,52 @@ func (v *AES256Vault) save() error {
 		return fmt.Errorf("failed to encrypt vault state: %w", err)
 	}
 
-	// write to the file atomically
-	if err := os.MkdirAll(filepath.Dir(v.fullPath), 0750); err != nil {
-		return fmt.Errorf("failed to create vault directory: %w", err)
-	}
-	tempFile := v.fullPath + ".tmp"
-	if err := os.WriteFile(tempFile, []byte(encryptedDataStr), 0600); err != nil {
-		return fmt.Errorf("failed to write temp vault file: %w", err)
-	}
-
-	if err := os.Rename(tempFile, v.fullPath); err != nil {
-		_ = os.Remove(tempFile)
-		return fmt.Errorf("failed to move vault file: %w", err)
-	}
+	return writeVaultFileAtomic(v.fullPath, []byte(encryptedDataStr))
+}
 
-	return nil
+// mutate runs a read-modify-write cycle under the cross-process vault lock.
+//
+// Reloading inside the lock is the point: in-memory state is a snapshot taken
+// when the provider was constructed, and every save rewrites the whole file.
+// Writing that snapshot back without refreshing silently discards whatever
+// another process stored in the meantime.
+func (v *AES256Vault) mutate(apply func() error) error {
+	return withVaultLock(v.fullPath, func() error {
+		if err := v.load(); err != nil {
+			return err
+		}
+		if err := apply(); err != nil {
+			return err
+		}
+		return v.save()
+	})
 }
 
 func (v *AES256Vault) ID() string {
 	return v.id
 }
 
-func (v *AES256Vault) Metadata() Metadata {
+func (v *AES256Vault) Metadata() (Metadata, error) {
 	v.mu.RLock()
 	defer v.mu.RUnlock()
 
 	if v.state == nil {
-		return Metadata{}
+		return Metadata{}, ErrVaultClosed
 	}
-	return v.state.Metadata
+	return v.state.Metadata, nil
 }
 
 func (v *AES256Vault) GetSecret(key string) (Secret, error) {
 	v.mu.RLock()
 	defer v.mu.RUnlock()
 
+	if err := ValidateSecretKey(key); err != nil {
+		return nil, err
+	}
+	if v.state == nil {
+		return nil, ErrVaultClosed
+	}
+
 	value, exists := v.state.Secrets[key]
 	if !exists {
 		return nil, ErrSecretNotFound
@@ -221,43 +246,68 @@ func (v *AES256Vault) SetSecret(key string, secret Secret) error {
 	if err := ValidateSecretKey(key); err != nil {
 		return err
 	}
-
-	if v.state.Secrets == nil {
-		v.state.Secrets = make(map[string]string)
+	if v.state == nil {
+		return ErrVaultClosed
 	}
 
-	v.state.Secrets[key] = secret.PlainTextString()
-	return v.save()
+	return v.mutate(func() error {
+		if v.state.Secrets == nil {
+			v.state.Secrets = make(map[string]string)
+		}
+		v.state.Secrets[key] = secret.PlainTextString()
+		return nil
+	})
 }
 
 func (v *AES256Vault) DeleteSecret(key string) error {
 	v.mu.Lock()
 	defer v.mu.Unlock()
 
-	_, exists := v.state.Secrets[key]
-	if !exists {
-		return ErrSecretNotFound
+	if err := ValidateSecretKey(key); err != nil {
+		return err
+	}
+	if v.state == nil {
+		return ErrVaultClosed
 	}
 
-	delete(v.state.Secrets, key)
-	return v.save()
+	// The existence check runs inside mutate, after the reload, so it sees the
+	// current on-disk contents rather than a stale snapshot.
+	return v.mutate(func() error {
+		if _, exists := v.state.Secrets[key]; !exists {
+			return ErrSecretNotFound
+		}
+		delete(v.state.Secrets, key)
+		return nil
+	})
 }
 
 func (v *AES256Vault) ListSecrets() ([]string, error) {
 	v.mu.RLock()
 	defer v.mu.RUnlock()
 
+	if v.state == nil {
+		return nil, ErrVaultClosed
+	}
+
 	keys := make([]string, 0, len(v.state.Secrets))
 	for k := range v.state.Secrets {
 		keys = append(keys, k)
 	}
+	sort.Strings(keys)
 	return keys, nil
 }
 
 func (v *AES256Vault) HasSecret(key string) (bool, error) {
 	v.mu.RLock()
 	defer v.mu.RUnlock()
 
+	if err := ValidateSecretKey(key); err != nil {
+		return false, err
+	}
+	if v.state == nil {
+		return false, ErrVaultClosed
+	}
+
 	_, exists := v.state.Secrets[key]
 	return exists, nil
 }
@@ -267,6 +317,9 @@ func (v *AES256Vault) Close() error {
 	v.mu.Lock()
 	defer v.mu.Unlock()
 
+	if v.state != nil {
+		clearSecrets(v.state.Secrets)
+	}
 	v.dek = ""
 	v.state = nil