feat: add elevated execution support to exec messages

protocols/docs/NOW-spec.md

@@ -3,7 +3,7 @@
 TOC is generated in [Obsidian](obsidian.md) via
 [TOC plugin](https://github.com/hipstersmoothie/obsidian-plugin-toc)
 -->
-# NOW-PROTO 1.6
+# NOW-PROTO 1.7
 - [Messages](#messages)
 	- [Transport](#transport)
 	- [Message Syntax](#message-syntax)
@@ -46,6 +46,7 @@ TOC is generated in [Obsidian](obsidian.md) via
 			- [NOW_EXEC_BATCH_MSG](#now_exec_batch_msg)
 			- [NOW_EXEC_WINPS_MSG](#now_exec_winps_msg)
 			- [NOW_EXEC_PWSH_MSG](#now_exec_pwsh_msg)
+			- [Elevated Execution](#elevated-execution)
 		- [RDM Messages](#rdm-messages)
 			- [NOW_RDM_MSG](#now_rdm_msg)
 			- [NOW_RDM_CAPABILITIES_MSG](#now_rdm_capabilities_msg)
@@ -328,6 +329,7 @@ increment major version; Protocol implementations with different major version a
 | NOW_CAP_EXEC_STYLE_PWSH<br>0x0020 | PowerShell 7 (.ps1) execution style. |
 | NOW_CAP_EXEC_UNICODE_CONSOLE<br>0x0040 | Host supports encoding control flags (RAW_ENCODING, UNICODE_CONSOLE, and ENCODING_UTF8). |
 | NOW_CAP_EXEC_IO_REDIRECTION<br>0x1000 | Set if host implements exec session IO redirection. |
+| NOW_CAP_EXEC_ELEVATE_SHELL<br>0x0080 | Set if host can elevate an exec session using the platform shell. Elevation may prompt the interactive user for consent, and IO redirection is unavailable for elevated sessions. See [Elevated Execution](#elevated-execution). |
 
 <!-- TODO: add AppleScript command -->
 
@@ -956,6 +958,7 @@ packet-beta
 | Flag                                   | Meaning                   |
 |----------------------------------------|---------------------------|
 | NOW_EXEC_FLAG_RUN_DIRECTORY_SET<br>0x0001 | `directory` field contains non-default value. |
+| NOW_EXEC_FLAG_RUN_ELEVATED<br>0x0002 | Execute the command with elevated privileges. The elevation mechanism is selected by the server and advertised in `execCapset`; see [Elevated Execution](#elevated-execution). |
 
 **sessionId (4 bytes)**: A 32-bit unsigned integer containing a unique remote execution session id.
 
@@ -993,6 +996,7 @@ packet-beta
 | NOW_EXEC_FLAG_PROCESS_PARAMETERS_SET<br>0x0001 | `parameters` field contains non-default value. |
 | NOW_EXEC_FLAG_PROCESS_DIRECTORY_SET<br>0x0002 | `directory` field contains non-default value.|
 | NOW_EXEC_FLAG_PROCESS_ENCODING_UTF8<br>0x0004 | Enables OEM-to-UTF-8 transcoding for stdin, stdout, and stderr. Without this flag, data streams are passed through as raw bytes without encoding conversion. |
+| NOW_EXEC_FLAG_PROCESS_ELEVATED<br>0x0008 | Execute the command with elevated privileges. The elevation mechanism is selected by the server and advertised in `execCapset`; see [Elevated Execution](#elevated-execution). |
 | NOW_EXEC_FLAG_PROCESS_IO_REDIRECTION<br>0x1000 | Enable stdio (stdout, stderr, stdin) redirection. |
 | NOW_EXEC_FLAG_PROCESS_DETACHED<br>0x8000 | Detached mode: the process is started without tracking execution or sending back output. |
 
@@ -1035,6 +1039,7 @@ packet-beta
 |----------------------------------------|---------------------------|
 | NOW_EXEC_FLAG_SHELL_SHELL_SET<br>0x0001 | `shell` field contains non-default value. |
 | NOW_EXEC_FLAG_SHELL_DIRECTORY_SET<br>0x0002 | `directory` field contains non-default value. |
+| NOW_EXEC_FLAG_SHELL_ELEVATED<br>0x0008 | Execute the command with elevated privileges. The elevation mechanism is selected by the server and advertised in `execCapset`; see [Elevated Execution](#elevated-execution). |
 | NOW_EXEC_FLAG_SHELL_IO_REDIRECTION<br>0x1000 | Enable stdio (stdout, stderr, stdin) redirection. |
 | NOW_EXEC_FLAG_SHELL_DETACHED<br>0x8000 | Detached mode: the shell is started without tracking execution or sending back output. |
 
@@ -1077,6 +1082,8 @@ packet-beta
 | NOW_EXEC_FLAG_BATCH_DIRECTORY_SET<br>0x0001 | `directory` field contains non-default value. |
 | NOW_EXEC_FLAG_BATCH_RAW_ENCODING<br>0x0002 | Disables the default OEM-to-UTF-8 transcoding: data streams are passed through as raw bytes without any encoding conversion. |
 | NOW_EXEC_FLAG_BATCH_UNICODE_CONSOLE<br>0x0004 | Enables Unicode console: agent injects `@chcp 65001 > nul` and writes the script in BOM-less UTF-8. Implies UTF-8 stdout/stderr streams. |
+| NOW_EXEC_FLAG_BATCH_ELEVATED<br>0x0008 | Execute the command with elevated privileges. The elevation mechanism is selected by the server and advertised in `execCapset`; see [Elevated Execution](#elevated-execution). |
+| NOW_EXEC_FLAG_BATCH_NO_EXIT<br>0x0010 | Keeps the command interpreter running after the batch file completes (`cmd /K` rather than `/C`). MUST be ignored when the session redirects stdio, where the hidden interpreter would never exit. |
 | NOW_EXEC_FLAG_BATCH_IO_REDIRECTION<br>0x1000 | Enable stdio (stdout, stderr, stdin) redirection. |
 | NOW_EXEC_FLAG_BATCH_DETACHED<br>0x8000 | Detached mode: the batch is started without tracking execution or sending back output. |
 
@@ -1132,6 +1139,7 @@ packet-beta
 | NOW_EXEC_FLAG_PS_DIRECTORY_SET<br>0x0100      | `directory` field contains non-default value and specifies command working directory                           |
 | NOW_EXEC_FLAG_PS_RAW_ENCODING<br>0x0200     | Disables the default OEM-to-UTF-8 transcoding: data streams are passed through as raw bytes without any encoding conversion. |
 | NOW_EXEC_FLAG_PS_UNICODE_CONSOLE<br>0x0400    | Enables Unicode console: agent injects `$OutputEncoding = [Console]::InputEncoding = [Console]::OutputEncoding = [System.Text.UTF8Encoding]::new()` at script start. Implies stdin/stdout/stderr streams are UTF-8. |
+| NOW_EXEC_FLAG_PS_ELEVATED<br>0x0800 | Execute the command with elevated privileges. The elevation mechanism is selected by the server and advertised in `execCapset`; see [Elevated Execution](#elevated-execution). |
 | NOW_EXEC_FLAG_PS_IO_REDIRECTION<br>0x1000     | Enable stdio (stdout, stderr, stdin) redirection.                                                              |
 | NOW_EXEC_FLAG_PS_SERVER_MODE<br>0x2000        | Run PowerShell in server mode.                                                                                 |
 | NOW_EXEC_FLAG_PS_DETACHED<br>0x8000           | Detached mode: PowerShell is started without tracking execution or sending back output.                        |
@@ -1196,6 +1204,50 @@ packet-beta
 
 **configurationName (variable)**: A NOW_VARSTR structure, same as with NOW_EXEC_WINPS_MSG.
 
+#### Elevated Execution
+
+Any exec message may request elevated execution by setting its `NOW_EXEC_FLAG_*_ELEVATED` flag.
+The flag expresses *intent* only: it never names a mechanism, and the client does not choose one.
+
+`ELEVATED` raises the privileges of the identity that would otherwise run the command, which is the
+session user. It does not select a different identity, and it carries no credentials. Running a
+command as another user is a separate concern and would be expressed by a separate field.
+
+**Requesting elevation.** A client SHOULD NOT set an `ELEVATED` flag unless the server advertised
+at least one `NOW_CAP_EXEC_ELEVATE_*` capability. A server that receives an `ELEVATED` flag without
+having advertised any elevation capability MUST fail the session with `NOW_CODE_NOT_IMPLEMENTED`.
+A server predating this version ignores the flag entirely and executes without elevation, so a
+client MUST NOT treat the absence of a failure as evidence that elevation took place: capability
+negotiation is the only reliable signal, and a client is expected to refuse the request locally
+when no elevation capability was advertised.
+A server MUST NOT execute a command without elevation after being asked to elevate it: silently
+downgrading the request denies the client any way to detect that privileges were not granted.
+
+**Mechanism selection.** The server selects the mechanism and advertises it in `execCapset`. Only
+`NOW_CAP_EXEC_ELEVATE_SHELL` is defined at present. A mechanism with different observable
+properties, such as one that raises no consent prompt or preserves stdio redirection, is expected to
+be advertised as an additional capability rather than by changing the meaning of an existing one, so
+a client always learns what to expect before it sends a request.
+
+**Semantics under NOW_CAP_EXEC_ELEVATE_SHELL.** The server elevates through the platform shell,
+which on Windows raises a consent prompt on the interactive user's desktop:
+
+- A client SHOULD omit `NOW_EXEC_FLAG_*_IO_REDIRECTION` when requesting elevation, and MUST NOT
+  assume the server honours it. The server MUST NOT open stdio channels for the session unless it
+  advertises a capability stating that elevated sessions keep their stdio.
+- Unless the request uses `NOW_EXEC_RUN_MSG`, which is never tracked, or sets
+  `NOW_EXEC_FLAG_*_DETACHED`, which promises no tracking, the server SHOULD still track the
+  session and report the real exit code in `NOW_EXEC_RESULT_MSG`, so a client can distinguish
+  success from failure without stdio.
+- `NOW_EXEC_ABORT_MSG` and `NOW_EXEC_CANCEL_REQ_MSG` MAY fail with `NOW_CODE_NOT_IMPLEMENTED`,
+  because the elevated child runs at a higher integrity level than the server's session process.
+- Elevation MAY require interactive consent, so the request MAY fail when no user is present to
+  grant it, or when the user declines.
+
+**Failure reporting.** A server that cannot grant elevation MUST report it distinctly rather than
+succeeding: the account has no elevated token available, the user declined consent, or elevation is
+not implemented for the requested exec style.
+
 ### RDM Messages
 
 #### NOW_RDM_MSG
@@ -1484,3 +1536,7 @@ packet-beta
 	- Add `NOW_EXEC_FLAG_PROCESS_ENCODING_UTF8` flag for process exec commands.
 	- Add `NOW_EXEC_FLAG_*_UNICODE_CONSOLE` flags for batch (cmd), winps, and pwsh exec commands.
 	- Add `NOW_CAP_EXEC_UNICODE_CONSOLE` capability flag.
+- 1.7
+	- Add `NOW_EXEC_FLAG_*_ELEVATED` flags for run, process, shell, batch, winps, and pwsh exec messages.
+	- Add `NOW_CAP_EXEC_ELEVATE_SHELL` capability flag.
+	- Add `NOW_EXEC_FLAG_BATCH_NO_EXIT` flag for batch exec commands.

protocols/dotnet/Devolutions.NowClient/src/AExecParams.cs

@@ -42,6 +42,12 @@ public StartedHandler OnStarted
             }
         }
 
+        /// <summary>
+        /// Whether the caller asked for elevated execution. Inspected by <see cref="NowClient"/>
+        /// so a request cannot be sent to a server that never advertised an elevation capability.
+        /// </summary>
+        internal bool IsElevated { get; set; }
+
         internal ExecSession ToExecSession(uint sessionId, ChannelWriter<IClientCommand> commandWriter)
         {
             return new ExecSession(

protocols/dotnet/Devolutions.NowClient/src/ExecBatchParams.cs

@@ -54,6 +54,26 @@ public ExecBatchParams UnicodeConsole(bool enable = true)
             return this;
         }
 
+        /// <summary>
+        /// Keep the command interpreter open after the batch file completes (`cmd /K` rather than
+        /// `/C`). Ignored by the server when the session redirects stdio.
+        /// </summary>
+        public ExecBatchParams NoExit(bool enable = true)
+        {
+            _noExit = enable;
+            return this;
+        }
+
+        /// <summary>
+        /// Execute with elevated privileges. Requires the host to advertise an elevation
+        /// capability; under shell-based elevation the session has no IO redirection.
+        /// </summary>
+        public ExecBatchParams Elevated(bool enable = true)
+        {
+            IsElevated = enable;
+            return this;
+        }
+
         internal NowMsgExecBatch ToNowMessage(uint sessionId)
         {
             var builder = new NowMsgExecBatch.Builder(sessionId, command);
@@ -83,6 +103,16 @@ internal NowMsgExecBatch ToNowMessage(uint sessionId)
                 builder.EnableUnicodeConsole();
             }
 
+            if (IsElevated)
+            {
+                builder.EnableElevated();
+            }
+
+            if (_noExit)
+            {
+                builder.EnableNoExit();
+            }
+
             return builder.Build();
         }
 
@@ -91,5 +121,6 @@ internal NowMsgExecBatch ToNowMessage(uint sessionId)
         private bool _detached = false;
         private bool _rawEncoding = false;
         private bool _unicodeConsole = false;
+        private bool _noExit = false;
     }
 }

protocols/dotnet/Devolutions.NowClient/src/ExecProcessParams.cs

@@ -1,4 +1,4 @@
-using Devolutions.NowProto.Messages;
+using Devolutions.NowProto.Messages;
 
 namespace Devolutions.NowClient
 {
@@ -54,6 +54,16 @@ public ExecProcessParams EncodingUtf8(bool enable = true)
             return this;
         }
 
+        /// <summary>
+        /// Execute with elevated privileges. Requires the host to advertise an elevation
+        /// capability; under shell-based elevation the session has no IO redirection.
+        /// </summary>
+        public ExecProcessParams Elevated(bool enable = true)
+        {
+            IsElevated = enable;
+            return this;
+        }
+
         internal NowMsgExecProcess ToNowMessage(uint sessionId)
         {
             var builder = new NowMsgExecProcess.Builder(sessionId, filename);
@@ -83,6 +93,11 @@ internal NowMsgExecProcess ToNowMessage(uint sessionId)
                 builder.EnableEncodingUtf8();
             }
 
+            if (IsElevated)
+            {
+                builder.EnableElevated();
+            }
+
             return builder.Build();
         }
 

protocols/dotnet/Devolutions.NowClient/src/ExecPwshParams.cs

@@ -127,6 +127,16 @@ public ExecPwshParams UnicodeConsole(bool enable = true)
             return this;
         }
 
+        /// <summary>
+        /// Execute with elevated privileges. Requires the host to advertise an elevation
+        /// capability; under shell-based elevation the session has no IO redirection.
+        /// </summary>
+        public ExecPwshParams Elevated(bool enable = true)
+        {
+            IsElevated = enable;
+            return this;
+        }
+
         internal NowMsgExecPwsh ToNowMessage(uint sessionId)
         {
             var builder = _serverMode
@@ -193,6 +203,11 @@ internal NowMsgExecPwsh ToNowMessage(uint sessionId)
                 builder.EnableUnicodeConsole();
             }
 
+            if (IsElevated)
+            {
+                builder.EnableElevated();
+            }
+
             return builder.Build();
         }
 

protocols/dotnet/Devolutions.NowClient/src/ExecRunParams.cs

@@ -18,6 +18,16 @@ public ExecRunParams Directory(string directory)
             return this;
         }
 
+        /// <summary>
+        /// Execute with elevated privileges. Requires the host to advertise an elevation
+        /// capability; under shell-based elevation the session has no IO redirection.
+        /// </summary>
+        public ExecRunParams Elevated(bool enable = true)
+        {
+            IsElevated = enable;
+            return this;
+        }
+
         internal NowMsgExecRun ToNowMessage(uint sessionId)
         {
             var builder = new NowMsgExecRun.Builder(sessionId, command);
@@ -27,6 +37,11 @@ internal NowMsgExecRun ToNowMessage(uint sessionId)
                 builder.Directory(_directory);
             }
 
+            if (IsElevated)
+            {
+                builder.EnableElevated();
+            }
+
             return builder.Build();
         }
 

protocols/dotnet/Devolutions.NowClient/src/ExecShellParams.cs

@@ -46,6 +46,16 @@ public ExecShellParams Detached(bool enable = true)
             return this;
         }
 
+        /// <summary>
+        /// Execute with elevated privileges. Requires the host to advertise an elevation
+        /// capability; under shell-based elevation the session has no IO redirection.
+        /// </summary>
+        public ExecShellParams Elevated(bool enable = true)
+        {
+            IsElevated = enable;
+            return this;
+        }
+
         internal NowMsgExecShell ToNowMessage(uint sessionId)
         {
             var builder = new NowMsgExecShell.Builder(sessionId, command);
@@ -70,6 +80,11 @@ internal NowMsgExecShell ToNowMessage(uint sessionId)
                 builder.EnableDetached();
             }
 
+            if (IsElevated)
+            {
+                builder.EnableElevated();
+            }
+
             return builder.Build();
         }
 

protocols/dotnet/Devolutions.NowClient/src/ExecWinPsParams.cs

@@ -128,6 +128,16 @@ public ExecWinPsParams UnicodeConsole(bool enable = true)
             return this;
         }
 
+        /// <summary>
+        /// Execute with elevated privileges. Requires the host to advertise an elevation
+        /// capability; under shell-based elevation the session has no IO redirection.
+        /// </summary>
+        public ExecWinPsParams Elevated(bool enable = true)
+        {
+            IsElevated = enable;
+            return this;
+        }
+
         internal NowMsgExecWinPs ToNowMessage(uint sessionId)
         {
             var builder = _serverMode
@@ -194,6 +204,11 @@ internal NowMsgExecWinPs ToNowMessage(uint sessionId)
                 builder.EnableUnicodeConsole();
             }
 
+            if (IsElevated)
+            {
+                builder.EnableElevated();
+            }
+
             return builder.Build();
         }