1 files changed, 9 insertions, 1 deletions

diff --git a/src/lib/libcrypto/bn/bn_mont.c b/src/lib/libcrypto/bn/bn_mont.c
index e92ceae5f4..314d683782 100644
--- a/src/lib/libcrypto/bn/bn_mont.c
+++ b/src/lib/libcrypto/bn/bn_mont.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_mont.c,v 1.50 2023/03/07 06:19:44 jsing Exp $ */
+/* $OpenBSD: bn_mont.c,v 1.51 2023/03/07 06:28:36 jsing Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -435,6 +435,14 @@ bn_mod_mul_montgomery(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
         if (mctx->N.top <= 1 || a->top != mctx->N.top || b->top != mctx->N.top)
                 return bn_mod_mul_montgomery_simple(r, a, b, mctx, ctx);
 
+        /*
+         * Legacy bn_mul_mont() performs stack based allocation, without
+         * size limitation. Allowing a large size results in the stack
+         * being blown.
+         */
+        if (mctx->N.top > (8 * 1024 / sizeof(BN_ULONG)))
+                return bn_montgomery_multiply(r, a, b, mctx, ctx);
+
         if (!bn_wexpand(r, mctx->N.top))
                 return 0;