Distrust publicly trusted SHA-1 certs

net/cert/cert_verify_proc.cc

Index: net/cert/cert_verify_proc.cc
diff --git a/net/cert/cert_verify_proc.cc b/net/cert/cert_verify_proc.cc
index c2c5930c305abd0a79d9eaf0767f7e659675cb3a..4d6584768dbc2e8be6f12b7038fd0cbf5674b22b 100644
--- a/net/cert/cert_verify_proc.cc
+++ b/net/cert/cert_verify_proc.cc
@@ -41,6 +41,7 @@
 #elif defined(OS_MACOSX)
 #include "net/cert/cert_verify_proc_mac.h"
 #elif defined(OS_WIN)
+#include "base/win/windows_version.h"
 #include "net/cert/cert_verify_proc_win.h"
 #else
 #error Implement certificate verification.
@@ -357,6 +358,17 @@ struct HashToArrayComparator {
   }
 };
 
+bool AreSHA1IntermediatesAllowed() {
+#if defined(OS_WIN)
+  // TODO(rsleevi): Remove this once https://crbug.com/588789 is resolved
+  // for Windows 7/2008 users.
+  // Note: This must be kept in sync with cert_verify_proc_unittest.
+  return base::win::GetVersion() >= base::win::VERSION_WIN8;
+#else
+  return false;
+#endif
+};
+
 }  // namespace
 
 // static
@@ -473,8 +485,21 @@ int CertVerifyProc::Verify(X509Certificate* cert,
   // TODO(mattm): apply the SHA-1 deprecation check to all certs unless
   // CertVerifier::VERIFY_ENABLE_SHA1_LOCAL_ANCHORS flag is present.
   if (verify_result->has_md5 ||
-      (verify_result->has_sha1_leaf && verify_result->is_issued_by_known_root &&
-       IsPastSHA1DeprecationDate(*cert))) {
+      // Current SHA-1 behaviour:
+      // - Reject all publicly trusted SHA-1
+      // - ... unless it's in the intermediate and SHA-1 intermediates are
+      //   allowed for that platform. See https://crbug.com/588789
+      (!base::FeatureList::IsEnabled(kSHA1LegacyMode) &&
+       (verify_result->is_issued_by_known_root &&
+        (verify_result->has_sha1_leaf ||
+         (verify_result->has_sha1 && !AreSHA1IntermediatesAllowed())))) ||
+      // Legacy SHA-1 behaviour:
+      // - Reject all publicly trusted SHA-1 leaf certs issued after
+      //   2016-01-01.
+      (base::FeatureList::IsEnabled(kSHA1LegacyMode) &&
+       (verify_result->has_sha1_leaf &&
+        verify_result->is_issued_by_known_root &&
+        IsPastSHA1DeprecationDate(*cert)))) {
     verify_result->cert_status |= CERT_STATUS_WEAK_SIGNATURE_ALGORITHM;
     // Avoid replacing a more serious error, such as an OS/library failure,
     // by ensuring that if verification failed, it failed with a certificate
@@ -747,4 +772,8 @@ bool CertVerifyProc::HasTooLongValidity(const X509Certificate& cert) {
   return false;
 }
 
+// static
+const base::Feature CertVerifyProc::kSHA1LegacyMode{
+    "SHA1LegacyMode", base::FEATURE_DISABLED_BY_DEFAULT};
+
 }  // namespace net