fix: reduce Windows 8.3-short-name detection false-positives (#23066)

Author: harshmathurx

packages/vite/src/node/server/middlewares/__tests__/static.spec.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test } from 'vitest'
-import { isFileInTargetPath } from '../static'
+import { isFileInTargetPath, looksLikeWindowsShortNamePath } from '../static'
 
 describe('isFileInTargetPath', () => {
   const cases = {
@@ -27,3 +27,38 @@ describe('isFileInTargetPath', () => {
     }
   }
 })
+
+describe('looksLikeWindowsShortNamePath', () => {
+  const shortNamePaths = [
+    // classic 8.3 short names
+    'C:/PROGRA~1/x',
+    'C:/PROGRA~1',
+    'C:/LONGFI~1.TXT',
+    'C:/MICROS~2/foo',
+    // short-name-looking directory ancestor, not just the basename
+    'C:/foo/DOCUME~1/bar.js',
+  ]
+  const legitimateTildePaths = [
+    // real-world case from the reported issue: `~` not followed by a digit
+    'C:/project/dist/0~rslib-runtime.js',
+    // ancestor directory containing a tilde that isn't short-name shaped
+    'C:/Users/foo~bar/project/index.js',
+    // tilde-prefixed name with no short-name-style prefix/digit suffix
+    'C:/Users/foo/~backup/index.js',
+    // prefix longer than the 6 characters a short name can have
+    'C:/project/confirmations~2/index.js',
+    // no tilde at all
+    'C:/Users/foo/project/index.js',
+  ]
+
+  for (const filePath of shortNamePaths) {
+    test(`looksLikeWindowsShortNamePath("${filePath}") is true`, () => {
+      expect(looksLikeWindowsShortNamePath(filePath)).toBe(true)
+    })
+  }
+  for (const filePath of legitimateTildePaths) {
+    test(`looksLikeWindowsShortNamePath("${filePath}") is false`, () => {
+      expect(looksLikeWindowsShortNamePath(filePath)).toBe(false)
+    })
+  }
+})

packages/vite/src/node/server/middlewares/static.ts

@@ -287,6 +287,24 @@ export function isFileInTargetPath(
 }
 
 const windowsDriveRE = /^[A-Z]:/i
+// A Windows 8.3 "short name" segment looks like `NAME~1` or `NAME~1.EXT`: at
+// most 6 non-`~`/`.` characters, a `~`, then digits, within a single path
+// segment. Matching only this shape (rather than any `~`) still blocks the
+// short-name aliasing bypass while allowing filenames that merely contain a
+// tilde, e.g. `0~rslib-runtime.js`.
+const windowsShortNameSegmentRE = /^[^~.]{1,6}~\d+(?:\.[^~.]{0,3})?$/
+
+/**
+ * Warning: parameters are not validated, only works with normalized absolute paths
+ */
+export function looksLikeWindowsShortNamePath(filePath: string): boolean {
+  return (
+    filePath.includes('~') &&
+    filePath
+      .split('/')
+      .some((segment) => windowsShortNameSegmentRE.test(segment))
+  )
+}
 
 /**
  * Warning: parameters are not validated, only works with normalized absolute paths
@@ -299,9 +317,12 @@ export function isFileLoadingAllowed(
 
   if (!fs.strict) return true
 
-  if (isWindows && filePath.includes('~')) {
-    // `~` is used for Windows 8.3 short names, which can be used to bypass the check.
-    // While is it valid to have files with `~` in the path, we disallow it to be safe.
+  if (isWindows && looksLikeWindowsShortNamePath(filePath)) {
+    // Windows 8.3 short names (e.g. `PROGRA~1`) can alias a different long
+    // path and can be used to bypass the check.
+    // While it is valid to have files named similar to automatically generated
+    // short names, it is unlikely that a user would create them, so we
+    // disallow them to be safe.
     return false
   }