From 98831c25d4609f7018217504cf2d6748cf0404cf Mon Sep 17 00:00:00 2001
From: jordan <jordan@wolfssl.com>
Date: Fri, 8 May 2026 15:26:57 -0500
Subject: [PATCH] wolfmath: check mpSz in wc_export_int.

---
 tests/api/test_wolfmath.c | 8 ++++++++
 wolfcrypt/src/wolfmath.c  | 8 ++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/tests/api/test_wolfmath.c b/tests/api/test_wolfmath.c
index 4c86856dd4..1e4b622727 100644
--- a/tests/api/test_wolfmath.c
+++ b/tests/api/test_wolfmath.c
@@ -193,6 +193,14 @@ int test_wc_export_int(void)
     ExpectIntEQ(wc_export_int(&mp, buf, &len, 0, WC_TYPE_HEX_STR), 0);
     /* hex version of 1234 is 04D2 and should be 4 digits + 1 null */
     ExpectIntEQ(len, 5);
+    mp_clear(&mp);
+
+    /* test mp_int too large for export buf */
+    len = sizeof(buf);
+    ExpectIntEQ(mp_init(&mp), MP_OKAY);
+    ExpectIntEQ(mp_set_bit(&mp, 257), 0);
+    ExpectIntEQ(wc_export_int(&mp, buf, &len, 0, WC_TYPE_UNSIGNED_BIN),
+        WC_NO_ERR_TRACE(BUFFER_E));
 
     mp_clear(&mp);
 #endif
diff --git a/wolfcrypt/src/wolfmath.c b/wolfcrypt/src/wolfmath.c
index 20258001b9..60cd6b965d 100644
--- a/wolfcrypt/src/wolfmath.c
+++ b/wolfcrypt/src/wolfmath.c
@@ -253,14 +253,18 @@ int wc_export_int(mp_int* mp, byte* buf, word32* len, word32 keySz,
     else {
         /* for WC_TYPE_UNSIGNED_BIN keySz is used to zero pad.
          * The key size is always returned as the size */
+        word32 mpSz = 0;
         if (*len < keySz) {
             *len = keySz;
             return BUFFER_E;
         }
         *len = keySz;
+        mpSz = (word32)mp_unsigned_bin_size(mp);
+        if (mpSz > keySz) {
+            return BUFFER_E;
+        }
         XMEMSET(buf, 0, *len);
-        err = mp_to_unsigned_bin(mp, buf +
-            (keySz - (word32)mp_unsigned_bin_size(mp)));
+        err = mp_to_unsigned_bin(mp, buf + (keySz - mpSz));
     }
 
     return err;