diff --git a/onnxruntime/core/providers/cpu/math/matmul_helper.h b/onnxruntime/core/providers/cpu/math/matmul_helper.h
index 9da7509eea2c6..41739dd6abbef 100644
--- a/onnxruntime/core/providers/cpu/math/matmul_helper.h
+++ b/onnxruntime/core/providers/cpu/math/matmul_helper.h
@@ -168,6 +168,10 @@ class MatMulComputeHelper {
       if (num_output_dims == 0) {
         // for left and right being both vector, output is scalar thus no shape
         ORT_RETURN_IF_NOT(M_ == 1 && N_ == 1, "M_ == 1 && N_ == 1 was false");
+        // Both inputs are 1D vectors: left(K) dot right(K) => scalar.
+        // Validate K dimensions match to prevent out-of-bounds reads.
+        ORT_RETURN_IF_NOT(K_ == right_shape[0],
+                          "MatMul dimension mismatch");
       } else {
         if (left_num_dims == 1) {
           ORT_RETURN_IF_NOT(num_dims_with_pad - 1 == num_output_dims, "num_dims_with_pad - 1 != num_output_dims");
diff --git a/onnxruntime/test/providers/cpu/math/matmul_integer_test.cc b/onnxruntime/test/providers/cpu/math/matmul_integer_test.cc
index 3562d8b009002..6f03f875673d0 100644
--- a/onnxruntime/test/providers/cpu/math/matmul_integer_test.cc
+++ b/onnxruntime/test/providers/cpu/math/matmul_integer_test.cc
@@ -504,5 +504,43 @@ TEST(MatmulIntegerOpTest, SharedPrepackedWeights) {
 }
 #endif
 
+// Regression test: 1D×1D inputs with mismatched K dimensions must fail
+// instead of causing an out-of-bounds read in the MLAS backend.
+TEST(MatmulIntegerOpTest, MatMulInteger_1D_DimensionMismatch) {
+  OpTester test("MatMulInteger", 10);
+  // Omit shape info so ONNX shape inference won't reject 1D inputs at graph build time.
+  test.AddShapeToTensorData(false);
+  // A is [5] (K=5), B is [1] (K=1) — vector×vector K dimensions don't match.
+  test.AddInput<uint8_t>("T1", {5}, {11, 7, 3, 10, 6});
+  test.AddInput<uint8_t>("T2", {1}, {1});
+  test.AddInput<uint8_t>("a_zero_point", {}, {0});
+  test.AddInput<uint8_t>("b_zero_point", {}, {0});
+  test.AddOutput<int32_t>("T3", {}, {0});
+
+  // Restrict to CPU — other EPs may not support 1D quantized inputs.
+  std::vector<std::unique_ptr<IExecutionProvider>> cpu_only;
+  cpu_only.push_back(DefaultCpuExecutionProvider());
+  test.Run(OpTester::ExpectResult::kExpectFailure, "MatMul dimension mismatch",
+           {}, nullptr, &cpu_only);
+}
+
+// Valid 1D×1D dot product: both vectors have the same K, producing scalar output.
+TEST(MatmulIntegerOpTest, MatMulInteger_1D_Valid) {
+  OpTester test("MatMulInteger", 10);
+  // Omit shape info so ONNX shape inference won't reject 1D inputs at graph build time.
+  test.AddShapeToTensorData(false);
+  // A=[2,3], B=[4,5] => scalar dot = 2*4 + 3*5 = 23
+  test.AddInput<uint8_t>("T1", {2}, {2, 3});
+  test.AddInput<uint8_t>("T2", {2}, {4, 5});
+  test.AddInput<uint8_t>("a_zero_point", {}, {0});
+  test.AddInput<uint8_t>("b_zero_point", {}, {0});
+  test.AddOutput<int32_t>("T3", {}, {23});
+
+  // Restrict to CPU — other EPs may not support 1D quantized inputs.
+  std::vector<std::unique_ptr<IExecutionProvider>> cpu_only;
+  cpu_only.push_back(DefaultCpuExecutionProvider());
+  test.Run(OpTester::ExpectResult::kExpectSuccess, "", {}, nullptr, &cpu_only);
+}
+
 }  // namespace test
 }  // namespace onnxruntime