diff --git a/packages/core/README.md b/packages/core/README.md
index e17aa8d6..6ca112d2 100644
--- a/packages/core/README.md
+++ b/packages/core/README.md
@@ -294,7 +294,7 @@ const filename = getFilenameFromContentDisposition(disposition)
 // 'report "Q2".csv'
 ```
 
-`generateContentDisposition()` preserves an ASCII-safe `filename="..."` value and also emits `filename*=` for UTF-8 aware clients.
+`generateContentDisposition()` emits the exact name in `filename*=` for UTF-8 aware clients, plus an ASCII-safe `filename="..."` fallback where non-ASCII characters, `;` and `=` become `_`, so quote-unaware parsers cannot misread it.
 
 ### Header helpers
 
diff --git a/packages/core/src/utils.test.ts b/packages/core/src/utils.test.ts
index 2b5f18f2..8780deda 100644
--- a/packages/core/src/utils.test.ts
+++ b/packages/core/src/utils.test.ts
@@ -22,7 +22,23 @@ describe('generateContentDisposition', () => {
     expect(generateContentDisposition('a\\b.txt')).toEqual('inline; filename="a\\\\b.txt"; filename*=utf-8\'\'a%5Cb.txt')
     // a trailing backslash must not escape the closing quote
     expect(generateContentDisposition('a\\')).toEqual('inline; filename="a\\\\"; filename*=utf-8\'\'a%5C')
-    expect(generateContentDisposition('a\\"; injected=x')).toEqual('inline; filename="a\\\\\\"; injected=x"; filename*=utf-8\'\'a%5C%22%3B%20injected%3Dx')
+    expect(generateContentDisposition('a\\"; injected=x')).toEqual('inline; filename="a\\\\\\"_ injected_x"; filename*=utf-8\'\'a%5C%22%3B%20injected%3Dx')
+  })
+
+  it('round-trip through getFilenameFromContentDisposition', () => {
+    const filenames = [
+      '',
+      'test.txt',
+      'invoice;filename*=utf-8\'\'invoice.exe;.pdf',
+      'a;filename="evil.exe".txt',
+      'a\\"; filename=evil.exe',
+      '!@#$%^%^&*()\'"=;.txt',
+      'テンプレ\'";ート.txt',
+    ]
+
+    for (const filename of filenames) {
+      expect(getFilenameFromContentDisposition(generateContentDisposition(filename))).toEqual(filename)
+    }
   })
 
   it('escape non-ASCII filenames', () => {
@@ -79,6 +95,25 @@ it('getFilenameFromContentDisposition', () => {
   expect(getFilenameFromContentDisposition('attachment; filename*=us-ascii\'en\'test.txt')).toEqual('test.txt')
   expect(getFilenameFromContentDisposition('attachment; filename*=iso-8859-1\'\'%E9.txt; filename="fallback.txt"')).toEqual('fallback.txt')
   expect(getFilenameFromContentDisposition('attachment; filename*=iso-8859-1\'\'%E9.txt')).toEqual(undefined)
+
+  // ';' and parameters inside a quoted-string are part of the value
+  expect(getFilenameFromContentDisposition('inline; filename="invoice;filename*=utf-8\'\'invoice.exe;.pdf"; filename*=utf-8\'\'invoice%3Bfilename%2A%3Dutf-8%27%27invoice.exe%3B.pdf')).toEqual('invoice;filename*=utf-8\'\'invoice.exe;.pdf')
+  expect(getFilenameFromContentDisposition('inline; filename="report;filename*=utf-8\'\'evil.exe"')).toEqual('report;filename*=utf-8\'\'evil.exe')
+  expect(getFilenameFromContentDisposition('inline; filename="a;filename=evil.exe"')).toEqual('a;filename=evil.exe')
+  expect(getFilenameFromContentDisposition('inline; x="; filename=evil.exe"; filename="good.txt"')).toEqual('good.txt')
+  expect(getFilenameFromContentDisposition('inline; x="\\"; filename=evil.exe"; filename="good.txt"')).toEqual('good.txt')
+
+  // an unterminated quoted-string runs to the end of the header
+  expect(getFilenameFromContentDisposition('inline; filename="a.txt; filename*=utf-8\'\'evil.exe')).toEqual(undefined)
+  expect(getFilenameFromContentDisposition('inline; x="; filename*=utf-8\'\'evil.exe')).toEqual(undefined)
+  expect(getFilenameFromContentDisposition('inline; filename="a\\"')).toEqual(undefined)
+
+  // quoted filename* is tolerated
+  expect(getFilenameFromContentDisposition('attachment; filename*="utf-8\'\'%E2%82%AC.txt"')).toEqual('€.txt')
+
+  // whitespace around '=' and parameter names are case-insensitive
+  expect(getFilenameFromContentDisposition('attachment; FileName = "test.txt"')).toEqual('test.txt')
+  expect(getFilenameFromContentDisposition('attachment; FILENAME*= UTF-8\'\'test.txt')).toEqual('test.txt')
 })
 
 describe('resolveStandardBodyHint', () => {
diff --git a/packages/core/src/utils.ts b/packages/core/src/utils.ts
index 927198e8..e3a17547 100644
--- a/packages/core/src/utils.ts
+++ b/packages/core/src/utils.ts
@@ -1,43 +1,64 @@
 import type { StandardBody, StandardBodyHint, StandardHeaders, StandardUrl } from './types'
 import { isAsyncIteratorObject, safeDecodeURIComponent, safeEncodeURIComponent, toArray } from '@standard-server/shared'
 
+const FALLBACK_FILENAME_UNSAFE_CHAR_REGEX = /[^\x20-\x7E]|[;=]/g
+const QUOTED_STRING_SPECIAL_CHAR_REGEX = /[\\"]/g
+const QUOTED_PAIR_REGEX = /\\(.)/g
+
+// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURIComponent#encoding_for_content-disposition_and_link_headers
+const EXT_VALUE_RESERVED_CHAR_REGEX = /['()*]/g
+const EXT_VALUE_ALLOWED_ESCAPE_REGEX = /%(7C|60|5E)/g
+
+// RFC 8187 ext-value: charset "'" [ language ] "'" value-chars
+const EXT_VALUE_REGEX = /^([^']*)'[^']*'(.*)$/
+const EXT_VALUE_SUPPORTED_CHARSET_REGEX = /^(?:utf-8|us-ascii)$/i
+
+const CONTENT_DISPOSITION_PARAM_REGEX = /[\s;]*([^;=]*)(?:=\s*(?:"((?:\\.|[^"\\])*)"[^;]*|"[\s\S]*|([^;]*)))?/y
+
 export function generateContentDisposition(filename: string, type: 'inline' | 'attachment' = 'inline'): string {
-  const encodedFilename = filename.replace(/[^\x20-\x7E]/g, '_').replace(/[\\"]/g, '\\$&')
+  const encodedFilename = filename
+    .replace(FALLBACK_FILENAME_UNSAFE_CHAR_REGEX, '_')
+    .replace(QUOTED_STRING_SPECIAL_CHAR_REGEX, '\\$&')
 
-  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURIComponent#encoding_for_content-disposition_and_link_headers
   const encodedFilenameStar = safeEncodeURIComponent(filename)
-    .replace(/['()*]/g, c => `%${c.charCodeAt(0).toString(16).toUpperCase()}`)
-    .replace(/%(7C|60|5E)/g, (str, hex) => String.fromCharCode(Number.parseInt(hex, 16)))
+    .replace(EXT_VALUE_RESERVED_CHAR_REGEX, c => `%${c.charCodeAt(0).toString(16).toUpperCase()}`)
+    .replace(EXT_VALUE_ALLOWED_ESCAPE_REGEX, (str, hex) => String.fromCharCode(Number.parseInt(hex, 16)))
 
   return `${type}; filename="${encodedFilename}"; filename*=utf-8''${encodedFilenameStar}`
 }
 
-export function getFilenameFromContentDisposition(contentDisposition: string): string | undefined {
-  const extValue = contentDisposition.match(/(?:^|;)\s*filename\*=([^;]*)/i)?.[1]?.trim()
+function getContentDispositionParam(contentDisposition: string, name: string): string | undefined {
+  CONTENT_DISPOSITION_PARAM_REGEX.lastIndex = 0
+
+  while (CONTENT_DISPOSITION_PARAM_REGEX.lastIndex < contentDisposition.length) {
+    const [, paramName = '', quoted, token] = CONTENT_DISPOSITION_PARAM_REGEX.exec(contentDisposition)!
 
-  // RFC 8187 ext-value: charset "'" [ language ] "'" value-chars
-  const extValueMatch = extValue?.match(/^([^']*)'[^']*'(.*)$/)
+    if (paramName.trimEnd().toLowerCase() === name) {
+      return quoted !== undefined
+        ? quoted.replace(QUOTED_PAIR_REGEX, '$1')
+        : token?.trim() || undefined
+    }
+  }
+
+  return undefined
+}
+
+export function getFilenameFromContentDisposition(contentDisposition: string): string | undefined {
+  const extValue = getContentDispositionParam(contentDisposition, 'filename*')
+  const extValueMatch = extValue?.match(EXT_VALUE_REGEX)
 
   if (extValueMatch) {
     const [, charset = '', encodedFilename = ''] = extValueMatch
 
-    if (/^(?:utf-8|us-ascii)$/i.test(charset)) {
+    if (EXT_VALUE_SUPPORTED_CHARSET_REGEX.test(charset)) {
       return safeDecodeURIComponent(encodedFilename)
     }
-    // unsupported charset: fall through to the plain filename param
   }
   else if (extValue) {
-    // lenient: some senders omit the charset prefix entirely
     return safeDecodeURIComponent(extValue)
   }
 
-  const filenameMatch = contentDisposition.match(/(?:^|;)\s*filename=(?:"((?:\\.|[^"\\])*)"|([^";]*))/i)
-
-  if (filenameMatch?.[1] !== undefined) {
-    return filenameMatch[1].replace(/\\(.)/g, '$1')
-  }
-
-  return filenameMatch?.[2]?.trim() || undefined
+  return getContentDispositionParam(contentDisposition, 'filename')
 }
 
 export function flattenStandardHeader(header: string | readonly string[] | undefined): string | undefined {