[Security] Prevent absolute path bypass in sanitizeRelativePath

packages/cli-kit/src/public/node/path.test.ts

@@ -1,5 +1,5 @@
-import {relativizePath, normalizePath, cwd, sniffForPath, commonParentDirectory} from './path.js'
-import {describe, test, expect} from 'vitest'
+import {relativizePath, normalizePath, cwd, sniffForPath, commonParentDirectory, sanitizeRelativePath} from './path.js'
+import {describe, test, expect, vi} from 'vitest'
 
 describe('relativize', () => {
   test('relativizes the path', () => {
@@ -93,3 +93,27 @@ describe('sniffForPath', () => {
     expect(path).toStrictEqual('/path/to/project')
   })
 })
+
+describe('sanitizeRelativePath', () => {
+  test('returns the path if it is relative and has no traversal', () => {
+    // Given
+    const path = 'some/path'
+    const warn = vi.fn()
+
+    // When
+    const got = sanitizeRelativePath(path, warn)
+
+    // Then
+    expect(got).toBe('some/path')
+    expect(warn).not.toHaveBeenCalled()
+  })
+
+  test('strips traversal and absolute path segments and warns', () => {
+    const warn = vi.fn()
+    expect(sanitizeRelativePath('some/../path', warn)).toBe('path')
+    expect(sanitizeRelativePath('/etc/passwd', warn)).toBe('etc/passwd')
+    expect(sanitizeRelativePath('\\some\\path', warn)).toBe('some/path')
+    expect(sanitizeRelativePath('C:\\Windows', warn)).toBe('Windows')
+    expect(warn).toHaveBeenCalledTimes(4)
+  })
+})

packages/cli-kit/src/public/node/path.ts

@@ -217,20 +217,26 @@ export function sniffForJson(argv = process.argv): boolean {
  * @returns The sanitized path (may be an empty string if all segments were traversal).
  */
 export function sanitizeRelativePath(input: string, warn: (msg: string) => void): string {
-  const segments = input.replace(/\\/g, '/').split('/')
+  const normalized = input.replace(/\\/g, '/')
+  const segments = normalized.split('/')
   const stack: string[] = []
   let stripped = false
+
+  if (normalized.startsWith('/') || /^[a-zA-Z]:/.test(normalized)) {
+    stripped = true
+  }
+
   for (const seg of segments) {
     if (seg === '..') {
       stripped = true
       stack.pop()
-    } else if (seg !== '.') {
+    } else if (seg !== '.' && seg !== '' && !/^[a-zA-Z]:$/.test(seg)) {
       stack.push(seg)
     }
   }
   const result = stack.join('/')
   if (stripped) {
-    warn(`Warning: path '${input}' contains '..' traversal — sanitized to '${result || '.'}'\n`)
+    warn(`Warning: path '${input}' is insecure (contains '..' or is absolute) — sanitized to '${result || '.'}'\n`)
   }
   return result
 }