From 3447575417b35b2c92878aea58fa89d95df95957 Mon Sep 17 00:00:00 2001
From: Justin Spahr-Summers <justin@anthropic.com>
Date: Tue, 5 Nov 2024 11:56:15 +0000
Subject: [PATCH 1/2] Inherit environment variables deemed safe by default

---
 src/client/stdio.ts | 61 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 54 insertions(+), 7 deletions(-)

diff --git a/src/client/stdio.ts b/src/client/stdio.ts
index 98f5b77f..9f1301d4 100644
--- a/src/client/stdio.ts
+++ b/src/client/stdio.ts
@@ -1,4 +1,5 @@
 import { ChildProcess, spawn } from "node:child_process";
+import process from "node:process";
 import { ReadBuffer, serializeMessage } from "../shared/stdio.js";
 import { JSONRPCMessage } from "../types.js";
 import { Transport } from "../shared/transport.js";
@@ -17,11 +18,61 @@ export type StdioServerParameters = {
   /**
    * The environment to use when spawning the process.
    *
-   * The environment is NOT inherited from the parent process by default.
+   * If not specified, the result of getDefaultEnvironment() will be used.
    */
-  env?: object;
+  env?: Record<string, string>;
 };
 
+/**
+ * Environment variables to inherit by default, if an environment is not explicitly given.
+ */
+export const DEFAULT_INHERITED_ENV_VARS =
+  process.platform === "win32"
+    ? [
+        "ALLUSERSPROFILE",
+        "APPDATA",
+        "HOMEDRIVE",
+        "HOMEPATH",
+        "LOCALAPPDATA",
+        "NUMBER_OF_PROCESSORS",
+        "OS",
+        "PATH",
+        "PATHEXT",
+        "PROCESSOR_ARCHITECTURE",
+        "SYSTEMDRIVE",
+        "SYSTEMROOT",
+        "TEMP",
+        "TMP",
+        "USERNAME",
+        "USERPROFILE",
+        "WINDIR",
+      ]
+    : /* list inspired by the default env inheritance of sudo */
+      ["HOME", "LOGNAME", "PATH", "SHELL", "TERM", "USER"];
+
+/**
+ * Returns a default environment object including only environment variables deemed safe to inherit.
+ */
+export function getDefaultEnvironment(): Record<string, string> {
+  const env: Record<string, string> = {};
+
+  for (const key of DEFAULT_INHERITED_ENV_VARS) {
+    const value = process.env[key];
+    if (value === undefined) {
+      continue;
+    }
+
+    if (value.startsWith("()")) {
+      // Skip functions, which are a security risk.
+      continue;
+    }
+
+    env[key] = value;
+  }
+
+  return env;
+}
+
 /**
  * Client transport for stdio: this will connect to a server by spawning a process and communicating with it over stdin/stdout.
  *
@@ -56,11 +107,7 @@ export class StdioClientTransport implements Transport {
         this._serverParams.command,
         this._serverParams.args ?? [],
         {
-          // The parent process may have sensitive secrets in its env, so don't inherit it automatically.
-          env:
-            this._serverParams.env === undefined
-              ? {}
-              : { ...this._serverParams.env },
+          env: this._serverParams.env ?? getDefaultEnvironment(),
           stdio: ["pipe", "pipe", "inherit"],
           signal: this._abortController.signal,
         },

From 08b89404a38977f7e3878f1bee9498831addc884 Mon Sep 17 00:00:00 2001
From: Justin Spahr-Summers <justin@anthropic.com>
Date: Tue, 5 Nov 2024 12:10:24 +0000
Subject: [PATCH 2/2] Trim Windows list down based on review

---
 src/client/stdio.ts | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/src/client/stdio.ts b/src/client/stdio.ts
index 9f1301d4..93b2550e 100644
--- a/src/client/stdio.ts
+++ b/src/client/stdio.ts
@@ -29,23 +29,17 @@ export type StdioServerParameters = {
 export const DEFAULT_INHERITED_ENV_VARS =
   process.platform === "win32"
     ? [
-        "ALLUSERSPROFILE",
         "APPDATA",
         "HOMEDRIVE",
         "HOMEPATH",
         "LOCALAPPDATA",
-        "NUMBER_OF_PROCESSORS",
-        "OS",
         "PATH",
-        "PATHEXT",
         "PROCESSOR_ARCHITECTURE",
         "SYSTEMDRIVE",
         "SYSTEMROOT",
         "TEMP",
-        "TMP",
         "USERNAME",
         "USERPROFILE",
-        "WINDIR",
       ]
     : /* list inspired by the default env inheritance of sudo */
       ["HOME", "LOGNAME", "PATH", "SHELL", "TERM", "USER"];