1 files changed, 9 insertions, 0 deletions
diff --git a/security/nss/fuzz/mpi_expmod_target.cc b/security/nss/fuzz/mpi_expmod_target.cc
index ed31da354..b9be5854f 100644
--- a/security/nss/fuzz/mpi_expmod_target.cc
+++ b/security/nss/fuzz/mpi_expmod_target.cc
@@ -19,6 +19,15 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
   auto modulus = get_modulus(data, size, ctx);
   // Compare with OpenSSL exp mod
   m1 = &std::get<1>(modulus);
+  // The exponent b (B) can get really big. Make it smaller if necessary.
+  if (MP_USED(&b) > 100) {
+    size_t shift = (MP_USED(&b) - 100) * MP_DIGIT_BIT;
+    mp_div_2d(&b, shift, &b, nullptr);
+    BN_rshift(B, B, shift);
+  }
+  check_equal(A, &a, max_size);
+  check_equal(B, &b, max_size);
+  check_equal(std::get<0>(modulus), m1, 3 * max_size);
   assert(mp_exptmod(&a, &b, m1, &c) == MP_OKAY);
   (void)BN_mod_exp(C, A, B, std::get<0>(modulus), ctx);
   check_equal(C, &c, 2 * max_size);