fix: block SystemRoot/WINDIR in workspace .env and harden reg.exe path resolution [AI-assisted] (#74454)

* fix: address issue

* fix: address PR review feedback

* Add changelog entry for PR #74454

---------

Co-authored-by: Devin Robison <drobison@nvidia.com>

src/infra/dotenv.test.ts

@@ -228,8 +228,10 @@ describe("loadDotEnv", () => {
             "HTTP_PROXY=http://evil-proxy:8080",
             "HOMEBREW_BREW_FILE=./evil-brew/bin/brew",
             "HOMEBREW_PREFIX=./evil-brew",
+            "SystemRoot=.\\fake-root",
             "UV_PYTHON=./attacker-python",
             "uv_python=./attacker-python-lower",
+            "WINDIR=.\\fake-windir",
           ].join("\n"),
         );
         await writeEnvFile(path.join(stateDir, ".env"), "BAR=from-global\n");
@@ -245,8 +247,10 @@ describe("loadDotEnv", () => {
         delete process.env.HTTP_PROXY;
         delete process.env.HOMEBREW_BREW_FILE;
         delete process.env.HOMEBREW_PREFIX;
+        delete process.env.SystemRoot;
         delete process.env.UV_PYTHON;
         delete process.env.uv_python;
+        delete process.env.WINDIR;
 
         loadDotEnv({ quiet: true });
 
@@ -262,8 +266,10 @@ describe("loadDotEnv", () => {
         expect(process.env.HTTP_PROXY).toBeUndefined();
         expect(process.env.HOMEBREW_BREW_FILE).toBeUndefined();
         expect(process.env.HOMEBREW_PREFIX).toBeUndefined();
+        expect(process.env.SystemRoot).toBeUndefined();
         expect(process.env.UV_PYTHON).toBeUndefined();
         expect(process.env.uv_python).toBeUndefined();
+        expect(process.env.WINDIR).toBeUndefined();
       });
     });
   });

src/infra/windows-install-roots.test.ts

@@ -171,25 +171,25 @@ describe("getWindowsProgramFilesRoots", () => {
 });
 
 describe("locateWindowsRegExe", () => {
-  it("prefers SystemRoot and WINDIR candidates over arbitrary drive scans", () => {
-    expect(
-      _private.getWindowsRegExeCandidates({
-        SystemRoot: "D:\\Windows",
-        WINDIR: "E:\\Windows",
-      }),
-    ).toEqual([
-      "D:\\Windows\\System32\\reg.exe",
-      "E:\\Windows\\System32\\reg.exe",
-      "C:\\Windows\\System32\\reg.exe",
-    ]);
+  it("uses the fixed Windows system reg.exe candidate", () => {
+    expect(_private.getWindowsRegExeCandidates()).toEqual(["C:\\Windows\\System32\\reg.exe"]);
   });
 
-  it("dedupes equivalent roots case-insensitively", () => {
-    expect(
-      _private.getWindowsRegExeCandidates({
-        SystemRoot: "D:\\Windows\\",
-        windir: "d:\\windows",
-      }),
-    ).toEqual(["D:\\Windows\\System32\\reg.exe", "C:\\Windows\\System32\\reg.exe"]);
+  it("does not resolve readable reg.exe files from env-derived roots", () => {
+    _resetWindowsInstallRootsForTests({
+      isReadableFile: (filePath) => filePath === "D:\\Windows\\System32\\reg.exe",
+    });
+
+    const originalEnv = process.env;
+    try {
+      process.env = {
+        ...originalEnv,
+        SystemRoot: "D:\\Windows",
+        WINDIR: "E:\\Windows",
+      };
+      expect(_private.locateWindowsRegExe()).toBeNull();
+    } finally {
+      process.env = originalEnv;
+    }
   });
 });

src/infra/windows-install-roots.ts

@@ -92,29 +92,12 @@ function getEnvValueCaseInsensitive(
   return actualKey ? env[actualKey] : undefined;
 }
 
-function getWindowsRegExeCandidates(env: Record<string, string | undefined>): readonly string[] {
-  const seen = new Set<string>();
-  const candidates: string[] = [];
-  for (const root of [
-    normalizeWindowsInstallRoot(getEnvValueCaseInsensitive(env, "SystemRoot")),
-    normalizeWindowsInstallRoot(getEnvValueCaseInsensitive(env, "WINDIR")),
-    DEFAULT_WINDOWS_SYSTEM_ROOT,
-  ]) {
-    if (!root) {
-      continue;
-    }
-    const key = normalizeLowercaseStringOrEmpty(root);
-    if (seen.has(key)) {
-      continue;
-    }
-    seen.add(key);
-    candidates.push(path.win32.join(root, "System32", "reg.exe"));
-  }
-  return candidates;
+function getWindowsRegExeCandidates(): readonly string[] {
+  return [path.win32.join(DEFAULT_WINDOWS_SYSTEM_ROOT, "System32", "reg.exe")];
 }
 
-function locateWindowsRegExe(env: Record<string, string | undefined> = process.env): string | null {
-  for (const candidate of getWindowsRegExeCandidates(env)) {
+function locateWindowsRegExe(): string | null {
+  for (const candidate of getWindowsRegExeCandidates()) {
     if (isReadableFileFn(candidate)) {
       return candidate;
     }
@@ -151,7 +134,7 @@ function runRegQuery(
 }
 
 function defaultQueryRegistryValue(key: string, valueName: string): string | null {
-  const regExe = locateWindowsRegExe(process.env);
+  const regExe = locateWindowsRegExe();
   if (!regExe) {
     return null;
   }