1 files changed, 51 insertions, 0 deletions
diff --git a/src/Agent.Windows/Security/ExecutablePolicy.cs b/src/Agent.Windows/Security/ExecutablePolicy.cs
new file mode 100644
index 0000000..3d20bfa
--- /dev/null
+++ b/src/Agent.Windows/Security/ExecutablePolicy.cs
@@ -0,0 +1,51 @@
+using System.Security.Cryptography;
+
+namespace Agent.Windows.Security;
+
+public sealed record ExecutableApproval(string Path, string Sha256);
+public sealed record VerifiedExecutable(string CanonicalPath, string Sha256);
+
+public sealed class ExecutablePolicy(IEnumerable<ExecutableApproval> approvals, bool allowShell)
+{
+    private readonly IReadOnlyDictionary<string, string> _approvals = approvals.ToDictionary(
+        approval => CanonicalPath.Resolve(approval.Path), approval => NormalizeHash(approval.Sha256), StringComparer.OrdinalIgnoreCase);
+
+    public VerifiedExecutable Verify(string executable)
+    {
+        string canonical = CanonicalPath.Resolve(executable);
+        if (!allowShell && IsShell(canonical)) throw new SandboxPolicyException("process.shell_denied", "Shell execution is disabled.");
+        if (!_approvals.TryGetValue(canonical, out string? approvedHash)) throw new SandboxPolicyException("process.path_denied", "Executable path is not approved.");
+        using FileStream stream = new(canonical, FileMode.Open, FileAccess.Read, FileShare.Read);
+        string actualHash = Convert.ToHexString(SHA256.HashData(stream));
+        if (!CryptographicOperations.FixedTimeEquals(Convert.FromHexString(approvedHash), Convert.FromHexString(actualHash)))
+            throw new SandboxPolicyException("process.hash_denied", "Executable SHA-256 does not match its approval.");
+        return new(canonical, actualHash);
+    }
+
+    public static string? ManagedEntryPoint(string executable, IReadOnlyList<string> arguments)
+    {
+        if (!Path.GetFileName(executable).Equals("dotnet.exe", StringComparison.OrdinalIgnoreCase) || arguments.Count == 0) return null;
+        if (arguments[0].Equals("exec", StringComparison.OrdinalIgnoreCase))
+        {
+            if (arguments.Count < 2 || arguments[1].StartsWith("-", StringComparison.Ordinal))
+                throw new SandboxPolicyException("process.managed_entry_invalid", "dotnet exec requires an explicit managed entry assembly as its next argument.");
+            return arguments[1];
+        }
+        return arguments[0].EndsWith(".dll", StringComparison.OrdinalIgnoreCase) ? arguments[0] : null;
+    }
+
+    public static string ComputeSha256(string executable)
+    {
+        using FileStream stream = new(CanonicalPath.Resolve(executable), FileMode.Open, FileAccess.Read, FileShare.Read);
+        return Convert.ToHexString(SHA256.HashData(stream));
+    }
+
+    private static bool IsShell(string path) => Path.GetFileName(path) is string name &&
+        (name.Equals("cmd.exe", StringComparison.OrdinalIgnoreCase) || name.Equals("powershell.exe", StringComparison.OrdinalIgnoreCase) || name.Equals("pwsh.exe", StringComparison.OrdinalIgnoreCase));
+    private static string NormalizeHash(string hash)
+    {
+        string normalized = hash.Replace("-", string.Empty, StringComparison.Ordinal).Trim().ToUpperInvariant();
+        if (normalized.Length != 64 || !normalized.All(Uri.IsHexDigit)) throw new ArgumentException("SHA-256 approval must contain 64 hexadecimal characters.", nameof(hash));
+        return normalized;
+    }
+}