security: harden remote URL validation at config parse time

Add strict security validation for remote URLs and remote names to prevent
injection attacks when multi-remote support lands.

Changes:
- Add ValidateRemoteURL() with control character rejection, CLI flag
  injection prevention, scheme allowlist, and per-scheme structural
  validation (host/path requirements)
- Add ValidateRemoteName() aligned with existing peer-name policy
  (letter-start, alphanumeric + hyphen/underscore, max 64 chars)
- Add MatchesRemotePattern() and ValidateRemoteURLWithPatterns() for
  enterprise lockdown via federation.allowed-remote-patterns config
- Move config validation from simple IsRemoteURL() classifier to strict
  ValidateRemoteURL() security boundary
- Add defense-in-depth validation in AddCLIRemote/RemoveCLIRemote
- Add validation at clone entry points (cache.Ensure, bootstrap)
- Tighten SCP-style URL regex to exclude control characters in path
- Add comprehensive test coverage for null bytes, control chars,
  newline injection, CLI flag injection, scheme validation, structural
  validation, remote name edge cases, and pattern matching

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: harry-miller-trimble

cmd/bd/config.go

@@ -515,20 +515,31 @@ func validateSyncConfig(repoPath string) []string {
 		issues = append(issues, "federation.remote: required for Dolt sync")
 	}
 
-	// Validate remote URL format
+	// Strict security validation of remote URL
 	if federationRemote != "" {
-		if !isValidRemoteURL(federationRemote) {
-			issues = append(issues, fmt.Sprintf("federation.remote: %q is not a valid remote URL (expected dolthub://, gs://, s3://, az://, file://, or standard git URL)", federationRemote))
+		if err := remotecache.ValidateRemoteURL(federationRemote); err != nil {
+			issues = append(issues, fmt.Sprintf("federation.remote: %s", err))
+		}
+	}
+
+	// Validate against allowed-remote-patterns if configured
+	if federationRemote != "" {
+		patterns := v.GetStringSlice("federation.allowed-remote-patterns")
+		if len(patterns) > 0 {
+			if err := remotecache.ValidateRemoteURLWithPatterns(federationRemote, patterns); err != nil {
+				issues = append(issues, fmt.Sprintf("federation.remote: %s", err))
+			}
 		}
 	}
 
 	return issues
 }
 
 // isValidRemoteURL validates remote URL formats for sync configuration.
-// Delegates to remotecache.IsRemoteURL for consistent URL classification.
-func isValidRemoteURL(url string) bool {
-	return remotecache.IsRemoteURL(url)
+// Uses strict security validation that checks structural correctness,
+// rejects control characters, and validates per-scheme requirements.
+func isValidRemoteURL(rawURL string) bool {
+	return remotecache.ValidateRemoteURL(rawURL) == nil
 }
 
 // findBeadsRepoRoot walks up from the given path to find the repo root (containing .beads)

cmd/bd/config_test.go

@@ -391,7 +391,7 @@ federation:
 		issues := validateSyncConfig(tmpDir)
 		found := false
 		for _, issue := range issues {
-			if strings.Contains(issue, "federation.remote") && strings.Contains(issue, "not a valid remote URL") {
+			if strings.Contains(issue, "federation.remote") && (strings.Contains(issue, "not a valid remote URL") || strings.Contains(issue, "no scheme") || strings.Contains(issue, "not allowed")) {
 				found = true
 				break
 			}
@@ -420,6 +420,66 @@ federation:
 			t.Errorf("Expected no issues for valid config, got: %v", issues)
 		}
 	})
+
+	t.Run("remote URL with null byte", func(t *testing.T) {
+		configContent := "prefix: test\nfederation:\n  remote: \"dolthub://org/repo\\x00evil\"\n"
+		if err := os.WriteFile(filepath.Join(beadsDir, "config.yaml"), []byte(configContent), 0644); err != nil {
+			t.Fatalf("Failed to write config.yaml: %v", err)
+		}
+
+		issues := validateSyncConfig(tmpDir)
+		found := false
+		for _, issue := range issues {
+			if strings.Contains(issue, "federation.remote") {
+				found = true
+				break
+			}
+		}
+		if !found {
+			t.Errorf("Expected issue about invalid remote URL with null byte, got: %v", issues)
+		}
+	})
+
+	t.Run("allowed-remote-patterns enforcement", func(t *testing.T) {
+		configContent := `prefix: test
+federation:
+  remote: "https://github.com/user/repo"
+  allowed-remote-patterns:
+    - "dolthub://myorg/*"
+`
+		if err := os.WriteFile(filepath.Join(beadsDir, "config.yaml"), []byte(configContent), 0644); err != nil {
+			t.Fatalf("Failed to write config.yaml: %v", err)
+		}
+
+		issues := validateSyncConfig(tmpDir)
+		found := false
+		for _, issue := range issues {
+			if strings.Contains(issue, "does not match") {
+				found = true
+				break
+			}
+		}
+		if !found {
+			t.Errorf("Expected issue about remote not matching allowed patterns, got: %v", issues)
+		}
+	})
+
+	t.Run("allowed-remote-patterns passes when matching", func(t *testing.T) {
+		configContent := `prefix: test
+federation:
+  remote: "dolthub://myorg/myrepo"
+  allowed-remote-patterns:
+    - "dolthub://myorg/*"
+`
+		if err := os.WriteFile(filepath.Join(beadsDir, "config.yaml"), []byte(configContent), 0644); err != nil {
+			t.Fatalf("Failed to write config.yaml: %v", err)
+		}
+
+		issues := validateSyncConfig(tmpDir)
+		if len(issues) != 0 {
+			t.Errorf("Expected no issues when remote matches allowed pattern, got: %v", issues)
+		}
+	})
 }
 
 func TestResolvedConfigRepoRoot(t *testing.T) {

internal/config/config.go

@@ -146,6 +146,7 @@ func Initialize() error {
 	// Federation configuration (optional Dolt remote)
 	v.SetDefault("federation.remote", "")      // e.g., dolthub://org/beads, gs://bucket/beads, s3://bucket/beads, az://account.blob.core.windows.net/container/beads
 	v.SetDefault("federation.sovereignty", "") // T1 | T2 | T3 | T4 (empty = no restriction)
+	v.SetDefault("federation.allowed-remote-patterns", []string{}) // glob patterns restricting allowed remote URLs (enterprise lockdown)
 
 	// Push configuration defaults
 	v.SetDefault("no-push", false)

internal/remotecache/cache.go

@@ -80,6 +80,9 @@ func (c *Cache) lockPath(remoteURL string) string {
 // DOLT_REMOTE_USER, DOLT_REMOTE_PASSWORD, or DoltHub credentials
 // configured via `dolt creds`.
 func (c *Cache) Ensure(ctx context.Context, remoteURL string) (string, error) {
+	if err := ValidateRemoteURL(remoteURL); err != nil {
+		return "", fmt.Errorf("invalid remote URL: %w", err)
+	}
 	if _, err := exec.LookPath("dolt"); err != nil {
 		return "", fmt.Errorf("dolt CLI not found (required for remote cache): %w", err)
 	}

internal/remotecache/url.go

@@ -3,6 +3,8 @@ package remotecache
 import (
 	"crypto/sha256"
 	"fmt"
+	"net/url"
+	"path"
 	"regexp"
 	"strings"
 )
@@ -21,8 +23,28 @@ var remoteSchemes = []string{
 	"git+https://",
 }
 
+// allowedSchemes is the set of recognized URL schemes for validation.
+var allowedSchemes = map[string]bool{
+	"dolthub":   true,
+	"gs":        true,
+	"s3":        true,
+	"az":        true,
+	"file":      true,
+	"https":     true,
+	"http":      true,
+	"ssh":       true,
+	"git+ssh":   true,
+	"git+https": true,
+}
+
 // gitSSHPattern matches SCP-style git remote URLs (user@host:path).
-var gitSSHPattern = regexp.MustCompile(`^[a-zA-Z0-9._-]+@[a-zA-Z0-9][a-zA-Z0-9._-]*:.+$`)
+// The path portion excludes control characters (0x00-0x1f, 0x7f).
+var gitSSHPattern = regexp.MustCompile(`^[a-zA-Z0-9._-]+@[a-zA-Z0-9][a-zA-Z0-9._-]*:[^\x00-\x1f\x7f]+$`)
+
+// validRemoteNameRegex matches valid remote names: starts with a letter,
+// contains only alphanumeric characters, hyphens, and underscores.
+// Aligned with peer-name validation in credentials.go.
+var validRemoteNameRegex = regexp.MustCompile(`^[a-zA-Z][a-zA-Z0-9_-]*$`)
 
 // IsRemoteURL returns true if s looks like a dolt remote URL rather than
 // a local filesystem path. Recognized schemes: dolthub://, https://, http://,
@@ -37,6 +59,169 @@ func IsRemoteURL(s string) bool {
 	return gitSSHPattern.MatchString(s)
 }
 
+// ValidateRemoteURL performs strict security validation on a remote URL.
+// It rejects URLs containing control characters (including null bytes),
+// validates structural correctness per scheme, and rejects leading dashes
+// that could be interpreted as CLI flags.
+//
+// This is a security boundary — all remote URLs should pass through this
+// before reaching exec.Command arguments or SQL parameters.
+func ValidateRemoteURL(rawURL string) error {
+	if rawURL == "" {
+		return fmt.Errorf("remote URL cannot be empty")
+	}
+
+	// Reject control characters (null bytes, newlines, tabs, etc.)
+	for i, c := range rawURL {
+		if c < 0x20 || c == 0x7f {
+			return fmt.Errorf("remote URL contains control character at position %d (0x%02x)", i, c)
+		}
+	}
+
+	// Reject leading dash (CLI flag injection via exec.Command arguments)
+	if strings.HasPrefix(rawURL, "-") {
+		return fmt.Errorf("remote URL must not start with a dash")
+	}
+
+	// SCP-style URLs (user@host:path) are validated separately
+	if gitSSHPattern.MatchString(rawURL) {
+		return validateSCPURL(rawURL)
+	}
+
+	// Parse as standard URL
+	return validateSchemeURL(rawURL)
+}
+
+// validateSchemeURL validates a scheme-based URL (https://, dolthub://, etc.)
+func validateSchemeURL(rawURL string) error {
+	// net/url doesn't understand git+ssh:// etc., so we normalize first
+	normalizedURL := rawURL
+	scheme := ""
+	if idx := strings.Index(rawURL, "://"); idx > 0 {
+		scheme = rawURL[:idx]
+		// For net/url parsing, replace git+ssh with a parseable scheme
+		if strings.HasPrefix(scheme, "git+") {
+			normalizedURL = rawURL[len(scheme)+3:] // strip scheme://
+			normalizedURL = "placeholder://" + normalizedURL
+		}
+	}
+
+	if scheme == "" {
+		return fmt.Errorf("remote URL has no scheme (expected one of: %s)", strings.Join(sortedSchemes(), ", "))
+	}
+
+	if !allowedSchemes[scheme] {
+		return fmt.Errorf("remote URL scheme %q is not allowed (expected one of: %s)", scheme, strings.Join(sortedSchemes(), ", "))
+	}
+
+	parsed, err := url.Parse(normalizedURL)
+	if err != nil {
+		return fmt.Errorf("remote URL is malformed: %w", err)
+	}
+
+	// Scheme-specific structural validation
+	switch scheme {
+	case "dolthub":
+		// dolthub://org/repo — requires org and repo
+		p := strings.TrimPrefix(parsed.Path, "/")
+		host := parsed.Host
+		combined := host
+		if p != "" {
+			combined = host + "/" + p
+		}
+		parts := strings.Split(combined, "/")
+		if len(parts) < 2 || parts[0] == "" || parts[1] == "" {
+			return fmt.Errorf("dolthub:// URL must have org/repo format (e.g., dolthub://myorg/myrepo)")
+		}
+	case "https", "http", "git+https":
+		if parsed.Host == "" {
+			return fmt.Errorf("%s:// URL must include a hostname", scheme)
+		}
+	case "ssh", "git+ssh":
+		if parsed.Host == "" {
+			return fmt.Errorf("%s:// URL must include a hostname", scheme)
+		}
+	case "s3", "gs":
+		// s3://bucket/path, gs://bucket/path — host is the bucket
+		if parsed.Host == "" {
+			return fmt.Errorf("%s:// URL must include a bucket name", scheme)
+		}
+	case "az":
+		// az://account.blob.core.windows.net/container/path
+		if parsed.Host == "" {
+			return fmt.Errorf("az:// URL must include a storage account hostname")
+		}
+	case "file":
+		// file:// is allowed with any path
+	}
+
+	return nil
+}
+
+// validateSCPURL validates an SCP-style URL (user@host:path)
+func validateSCPURL(rawURL string) error {
+	// Already matched gitSSHPattern, so structure is valid.
+	// Extract host and verify no control chars (already checked above).
+	atIdx := strings.Index(rawURL, "@")
+	colonIdx := strings.Index(rawURL[atIdx:], ":")
+	if atIdx < 0 || colonIdx < 0 {
+		return fmt.Errorf("SCP-style URL must be in user@host:path format")
+	}
+	return nil
+}
+
+// ValidateRemoteName checks that a remote name is safe for use as a Dolt
+// remote identifier. Names must start with a letter and contain only
+// alphanumeric characters, hyphens, and underscores. Max 64 characters.
+func ValidateRemoteName(name string) error {
+	if name == "" {
+		return fmt.Errorf("remote name cannot be empty")
+	}
+	if len(name) > 64 {
+		return fmt.Errorf("remote name too long (max 64 characters)")
+	}
+	if strings.HasPrefix(name, "-") {
+		return fmt.Errorf("remote name must not start with a dash")
+	}
+	if !validRemoteNameRegex.MatchString(name) {
+		return fmt.Errorf("remote name must start with a letter and contain only alphanumeric characters, hyphens, and underscores")
+	}
+	return nil
+}
+
+// MatchesRemotePattern checks whether a URL matches a glob-style pattern.
+// Patterns use path.Match semantics (e.g., "dolthub://myorg/*").
+func MatchesRemotePattern(rawURL, pattern string) bool {
+	matched, err := path.Match(pattern, rawURL)
+	if err != nil {
+		return false
+	}
+	return matched
+}
+
+// ValidateRemoteURLWithPatterns validates a URL and optionally checks it
+// against an allowlist of glob patterns. If patterns is empty, only
+// structural validation is performed.
+func ValidateRemoteURLWithPatterns(rawURL string, patterns []string) error {
+	if err := ValidateRemoteURL(rawURL); err != nil {
+		return err
+	}
+	if len(patterns) == 0 {
+		return nil
+	}
+	for _, p := range patterns {
+		if MatchesRemotePattern(rawURL, p) {
+			return nil
+		}
+	}
+	return fmt.Errorf("remote URL %q does not match any allowed pattern", rawURL)
+}
+
+func sortedSchemes() []string {
+	// Return in a consistent display order
+	return []string{"dolthub", "https", "http", "ssh", "git+ssh", "git+https", "s3", "gs", "az", "file"}
+}
+
 // CacheKey returns a filesystem-safe identifier for a remote URL.
 // It uses the first 16 hex characters (64 bits) of the SHA-256 hash.
 // Birthday-bound collision risk is negligible for a local cache: 50% at