feat(fetch): implement spec compliant integrity checks (nodejs#1613)

Author: KhafraDev

lib/fetch/index.js

@@ -13,7 +13,7 @@ const { Headers } = require('./headers')
 const { Request, makeRequest } = require('./request')
 const zlib = require('zlib')
 const {
-  matchRequestIntegrity,
+  bytesMatch,
   makePolicyContainer,
   clonePolicyContainer,
   requestBadPort,
@@ -725,7 +725,7 @@ async function mainFetch (fetchParams, recursive = false) {
     const processBody = (bytes) => {
       // 1. If bytes do not match request’s integrity metadata,
       // then run processBodyError and abort these steps. [SRI]
-      if (!matchRequestIntegrity(request, bytes)) {
+      if (!bytesMatch(bytes, request.integrity)) {
         processBodyError('integrity mismatch')
         return
       }

lib/fetch/util.js

@@ -5,10 +5,19 @@ const { performance } = require('perf_hooks')
 const { isBlobLike, toUSVString, ReadableStreamFrom } = require('../core/util')
 const assert = require('assert')
 const { isUint8Array } = require('util/types')
-const { createHash } = require('crypto')
 
 let File
 
+// https://nodejs.org/api/crypto.html#determining-if-crypto-support-is-unavailable
+/** @type {import('crypto')|undefined} */
+let crypto
+
+try {
+  crypto = require('crypto')
+} catch {
+
+}
+
 // https://fetch.spec.whatwg.org/#block-bad-port
 const badPorts = [
   '1', '7', '9', '11', '13', '15', '17', '19', '20', '21', '22', '23', '25', '37', '42', '43', '53', '69', '77', '79',
@@ -341,9 +350,114 @@ function determineRequestsReferrer (request) {
   return 'no-referrer'
 }
 
-function matchRequestIntegrity (request, bytes) {
-  const [algo, expectedHashValue] = request.integrity.split('-', 2)
-  return createHash(algo).update(bytes).digest('hex') === expectedHashValue
+/**
+ * @see https://w3c.github.io/webappsec-subresource-integrity/#does-response-match-metadatalist
+ * @param {Uint8Array} bytes
+ * @param {string} metadataList
+ */
+function bytesMatch (bytes, metadataList) {
+  // If node is not built with OpenSSL support, we cannot check
+  // a request's integrity, so allow it by default (the spec will
+  // allow requests if an invalid hash is given, as precedence).
+  /* istanbul ignore if: only if node is built with --without-ssl */
+  if (crypto === undefined) {
+    return true
+  }
+
+  // 1. Let parsedMetadata be the result of parsing metadataList.
+  const parsedMetadata = parseMetadata(metadataList)
+
+  // 2. If parsedMetadata is no metadata, return true.
+  if (parsedMetadata === 'no metadata') {
+    return true
+  }
+
+  // 3. If parsedMetadata is the empty set, return true.
+  if (parsedMetadata.length === 0) {
+    return true
+  }
+
+  // 4. Let metadata be the result of getting the strongest
+  //    metadata from parsedMetadata.
+  // Note: this will only work for SHA- algorithms and it's lazy *at best*.
+  const metadata = parsedMetadata.sort((c, d) => d.algo.localeCompare(c.algo))
+
+  // 5. For each item in metadata:
+  for (const item of metadata) {
+    // 1. Let algorithm be the alg component of item.
+    const algorithm = item.algo
+
+    // 2. Let expectedValue be the val component of item.
+    const expectedValue = item.hash
+
+    // 3. Let actualValue be the result of applying algorithm to bytes.
+    // Note: "applying algorithm to bytes" converts the result to base64
+    const actualValue = crypto.createHash(algorithm).update(bytes).digest('base64')
+
+    // 4. If actualValue is a case-sensitive match for expectedValue,
+    //    return true.
+    if (actualValue === expectedValue) {
+      return true
+    }
+  }
+
+  // 6. Return false.
+  return false
+}
+
+// https://w3c.github.io/webappsec-subresource-integrity/#grammardef-hash-with-options
+// hash-algo is defined in Content Security Policy 2 Section 4.2
+// base64-value is similary defined there
+// VCHAR is defined https://www.rfc-editor.org/rfc/rfc5234#appendix-B.1
+const parseHashWithOptions = /((?<algo>sha256|sha384|sha512)-(?<hash>[A-z0-9+/]{1}.*={1,2}))( +[\x21-\x7e]?)?/i
+
+/**
+ * @see https://w3c.github.io/webappsec-subresource-integrity/#parse-metadata
+ * @param {string} metadata
+ */
+function parseMetadata (metadata) {
+  // 1. Let result be the empty set.
+  /** @type {{ algo: string, hash: string }[]} */
+  const result = []
+
+  // 2. Let empty be equal to true.
+  let empty = true
+
+  const supportedHashes = crypto.getHashes()
+
+  // 3. For each token returned by splitting metadata on spaces:
+  for (const token of metadata.split(' ')) {
+    // 1. Set empty to false.
+    empty = false
+
+    // 2. Parse token as a hash-with-options.
+    const parsedToken = parseHashWithOptions.exec(token)
+
+    // 3. If token does not parse, continue to the next token.
+    if (parsedToken === null || parsedToken.groups === undefined) {
+      // Note: Chromium blocks the request at this point, but Firefox
+      // gives a warning that an invalid integrity was given. The
+      // correct behavior is to ignore these, and subsequently not
+      // check the integrity of the resource.
+      continue
+    }
+
+    // 4. Let algorithm be the hash-algo component of token.
+    const algorithm = parsedToken.groups.algo
+
+    // 5. If algorithm is a hash function recognized by the user
+    //    agent, add the parsed token to result.
+    if (supportedHashes.includes(algorithm.toLowerCase())) {
+      result.push(parsedToken.groups)
+    }
+  }
+
+  // 4. Return no metadata if empty is true, otherwise return result.
+  if (empty === true) {
+    return 'no metadata'
+  }
+
+  return result
 }
 
 // https://w3c.github.io/webappsec-upgrade-insecure-requests/#upgrade-request
@@ -501,7 +615,6 @@ module.exports = {
   toUSVString,
   tryUpgradeRequestToAPotentiallyTrustworthyURL,
   coarsenedSharedCurrentTime,
-  matchRequestIntegrity,
   determineRequestsReferrer,
   makePolicyContainer,
   clonePolicyContainer,
@@ -528,5 +641,6 @@ module.exports = {
   isValidHeaderValue,
   hasOwn,
   isErrorLike,
-  fullyReadBody
+  fullyReadBody,
+  bytesMatch
 }

test/fetch/integrity.js

@@ -2,9 +2,12 @@
 
 const { test } = require('tap')
 const { createServer } = require('http')
-const { createHash } = require('crypto')
+const { createHash, getHashes } = require('crypto')
 const { gzipSync } = require('zlib')
 const { fetch, setGlobalDispatcher, Agent } = require('../..')
+const { once } = require('events')
+
+const supportedHashes = getHashes()
 
 setGlobalDispatcher(new Agent({
   keepAliveTimeout: 1,
@@ -44,7 +47,7 @@ test('request with wrong integrity checksum', (t) => {
     fetch(`http://localhost:${server.address().port}`, {
       integrity: `sha256-${hash}`
     }).then(response => {
-      t.fail('fetch did not fail')
+      t.pass('request did not fail')
     }).catch((err) => {
       t.equal(err.cause.message, 'integrity mismatch')
     }).finally(() => {
@@ -72,3 +75,76 @@ test('request with integrity checksum on encoded body', (t) => {
     t.end()
   })
 })
+
+test('request with a totally incorrect integrity', async (t) => {
+  const server = createServer((req, res) => {
+    res.end()
+  }).listen(0)
+
+  t.teardown(server.close.bind(server))
+  await once(server, 'listening')
+
+  await t.resolves(fetch(`http://localhost:${server.address().port}`, {
+    integrity: 'what-integrityisthis'
+  }))
+})
+
+test('request with mixed in/valid integrities', async (t) => {
+  const body = 'Hello world!'
+  const hash = createHash('sha256').update(body).digest('base64')
+
+  const server = createServer((req, res) => {
+    res.end(body)
+  }).listen(0)
+
+  t.teardown(server.close.bind(server))
+  await once(server, 'listening')
+
+  await t.resolves(fetch(`http://localhost:${server.address().port}`, {
+    integrity: `invalid-integrity sha256-${hash}`
+  }))
+})
+
+test('request with sha384 hash', { skip: !supportedHashes.includes('sha384') }, async (t) => {
+  const body = 'Hello world!'
+  const hash = createHash('sha384').update(body).digest('base64')
+
+  const server = createServer((req, res) => {
+    res.end(body)
+  }).listen(0)
+
+  t.teardown(server.close.bind(server))
+  await once(server, 'listening')
+
+  // request should succeed
+  await t.resolves(fetch(`http://localhost:${server.address().port}`, {
+    integrity: `sha384-${hash}`
+  }))
+
+  // request should fail
+  await t.rejects(fetch(`http://localhost:${server.address().port}`, {
+    integrity: 'sha384-ypeBEsobvcr6wjGzmiPcTaeG7/gUfE5yuYB3ha/uSLs='
+  }))
+})
+
+test('request with sha512 hash', { skip: !supportedHashes.includes('sha512') }, async (t) => {
+  const body = 'Hello world!'
+  const hash = createHash('sha512').update(body).digest('base64')
+
+  const server = createServer((req, res) => {
+    res.end(body)
+  }).listen(0)
+
+  t.teardown(server.close.bind(server))
+  await once(server, 'listening')
+
+  // request should succeed
+  await t.resolves(fetch(`http://localhost:${server.address().port}`, {
+    integrity: `sha512-${hash}`
+  }))
+
+  // request should fail
+  await t.rejects(fetch(`http://localhost:${server.address().port}`, {
+    integrity: 'sha512-ypeBEsobvcr6wjGzmiPcTaeG7/gUfE5yuYB3ha/uSLs='
+  }))
+})