diff --git a/common/changes/@rushstack/package-deps-hash/fix-skip-windows-reserved-filenames_2026-05-17-19-30.json b/common/changes/@rushstack/package-deps-hash/fix-skip-windows-reserved-filenames_2026-05-17-19-30.json
new file mode 100644
index 00000000000..0fc5923aa12
--- /dev/null
+++ b/common/changes/@rushstack/package-deps-hash/fix-skip-windows-reserved-filenames_2026-05-17-19-30.json
@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "comment": "Skip untracked files whose basename is a Windows reserved device name (e.g. `nul`, `con`, `aux`, `com1`-`com9`, `lpt1`-`lpt9`) when computing repo state on Windows. `git hash-object` cannot open such paths and otherwise aborts the entire repo-state calculation.",
+      "type": "patch",
+      "packageName": "@rushstack/package-deps-hash"
+    }
+  ],
+  "packageName": "@rushstack/package-deps-hash",
+  "email": "sshaurya914@gmail.com"
+}
diff --git a/libraries/package-deps-hash/src/getRepoState.ts b/libraries/package-deps-hash/src/getRepoState.ts
index cdc489bf9b9..7f01cde1620 100644
--- a/libraries/package-deps-hash/src/getRepoState.ts
+++ b/libraries/package-deps-hash/src/getRepoState.ts
@@ -28,6 +28,29 @@ const STANDARD_GIT_OPTIONS: readonly string[] = [
   'maintenance.auto=false'
 ];
 
+// Windows reserved device names (case-insensitive). A file whose final path segment matches one
+// of these (with or without an extension) cannot be opened by name on Windows, so passing it to
+// `git hash-object` aborts the process. Such files are typically untracked artifacts left behind
+// by tooling (e.g. stray `nul` from a shell redirect).
+const WINDOWS_RESERVED_BASENAMES: ReadonlySet<string> = new Set([
+  'CON', 'PRN', 'AUX', 'NUL',
+  'COM1', 'COM2', 'COM3', 'COM4', 'COM5', 'COM6', 'COM7', 'COM8', 'COM9',
+  'LPT1', 'LPT2', 'LPT3', 'LPT4', 'LPT5', 'LPT6', 'LPT7', 'LPT8', 'LPT9'
+]);
+
+/**
+ * Returns `true` if `filePath`'s final path segment is a Windows reserved device name
+ * (with or without an extension), case-insensitively. Exported for tests.
+ * @internal
+ */
+export function isWindowsReservedPath(filePath: string): boolean {
+  const lastSlash: number = Math.max(filePath.lastIndexOf('/'), filePath.lastIndexOf('\\'));
+  const basename: string = lastSlash >= 0 ? filePath.slice(lastSlash + 1) : filePath;
+  const dot: number = basename.indexOf('.');
+  const stem: string = (dot >= 0 ? basename.slice(0, dot) : basename).toUpperCase();
+  return WINDOWS_RESERVED_BASENAMES.has(stem);
+}
+
 const OBJECTMODE_SUBMODULE: '160000' = '160000';
 const OBJECTMODE_SYMLINK: '120000' = '120000';
 const OBJECTMODE_FILE_NONEXECUTABLE: '100644' = '100644';
@@ -480,8 +503,15 @@ export async function getDetailedRepoStateAsync(
 
     const [{ files, symlinks }, locallyModified] = await Promise.all([statePromise, locallyModifiedPromise]);
 
+    const isWindows: boolean = process.platform === 'win32';
     for (const [filePath, exists] of locallyModified) {
       if (exists && !symlinks.has(filePath)) {
+        // Skip Windows reserved device names. `git hash-object` cannot open them and would abort
+        // the entire repo-state computation. These are almost always stray artifacts (e.g. a `nul`
+        // file produced by a misdirected shell redirect) rather than meaningful inputs.
+        if (isWindows && isWindowsReservedPath(filePath)) {
+          continue;
+        }
         yield filePath;
       } else {
         files.delete(filePath);
diff --git a/libraries/package-deps-hash/src/test/getRepoState.test.ts b/libraries/package-deps-hash/src/test/getRepoState.test.ts
index c1422367b0f..573657feb36 100644
--- a/libraries/package-deps-hash/src/test/getRepoState.test.ts
+++ b/libraries/package-deps-hash/src/test/getRepoState.test.ts
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation. All rights reserved. Licensed under the MIT license.
 // See LICENSE in the project root for license information.
 
-import { parseGitStatus, parseGitVersion } from '../getRepoState';
+import { isWindowsReservedPath, parseGitStatus, parseGitVersion } from '../getRepoState';
 
 describe(parseGitVersion.name, () => {
   it('Can parse valid git version responses', () => {
@@ -87,3 +87,32 @@ describe(parseGitStatus.name, () => {
     expect(result.get(files[2])).toEqual(true);
   });
 });
+
+describe(isWindowsReservedPath.name, () => {
+  it('detects bare reserved basenames', () => {
+    expect(isWindowsReservedPath('nul')).toBe(true);
+    expect(isWindowsReservedPath('NUL')).toBe(true);
+    expect(isWindowsReservedPath('Con')).toBe(true);
+    expect(isWindowsReservedPath('com1')).toBe(true);
+    expect(isWindowsReservedPath('LPT9')).toBe(true);
+  });
+
+  it('detects reserved basenames with an extension', () => {
+    expect(isWindowsReservedPath('nul.txt')).toBe(true);
+    expect(isWindowsReservedPath('aux.log.bak')).toBe(true);
+  });
+
+  it('matches the final segment of nested paths with either slash style', () => {
+    expect(isWindowsReservedPath('apps/admin/nul')).toBe(true);
+    expect(isWindowsReservedPath('apps\\admin\\nul')).toBe(true);
+    expect(isWindowsReservedPath('apps/admin/sub/CON.tmp')).toBe(true);
+  });
+
+  it('does not match non-reserved names', () => {
+    expect(isWindowsReservedPath('null')).toBe(false);
+    expect(isWindowsReservedPath('console.ts')).toBe(false);
+    expect(isWindowsReservedPath('com.ts')).toBe(false);
+    expect(isWindowsReservedPath('lpt10')).toBe(false);
+    expect(isWindowsReservedPath('packages/nul-suffix/index.ts')).toBe(false);
+  });
+});