diff --git a/tensorflow/security/fuzzing/BUILD b/tensorflow/security/fuzzing/BUILD
index 93c03286b6c9fb..2f560bc3c6b711 100644
--- a/tensorflow/security/fuzzing/BUILD
+++ b/tensorflow/security/fuzzing/BUILD
@@ -26,3 +26,42 @@ tf_fuzz_target(
         "//tensorflow/core/platform:status",
     ],
 )
+
+tf_fuzz_target(
+    name = "consume_non_whitespace_fuzz",
+    srcs = ["consume_non_whitespace_fuzz.cc"],
+    deps = [
+        "//tensorflow/core/platform:str_util",
+        "//tensorflow/core/platform:stringpiece",
+    ],
+)
+
+tf_fuzz_target(
+    name = "consume_leading_digits_fuzz",
+    srcs = ["consume_leading_digits_fuzz.cc"],
+    deps = [
+        "//tensorflow/core/platform:str_util",
+        "//tensorflow/core/platform:stringpiece",
+    ],
+)
+
+tf_fuzz_target(
+    name = "arg_def_case_fuzz",
+    srcs = ["arg_def_case_fuzz.cc"],
+    tags = [
+        "notap",  # TODO(b/160990158): ArgDefCase invariant is broken
+    ],
+    deps = [
+        "//tensorflow/core/platform:str_util",
+        "//tensorflow/core/platform:stringpiece",
+    ],
+)
+
+tf_fuzz_target(
+    name = "string_replace_fuzz",
+    srcs = ["string_replace_fuzz.cc"],
+    deps = [
+        "//tensorflow/core/platform:str_util",
+        "//tensorflow/core/platform:stringpiece",
+    ],
+)
diff --git a/tensorflow/security/fuzzing/arg_def_case_fuzz.cc b/tensorflow/security/fuzzing/arg_def_case_fuzz.cc
new file mode 100644
index 00000000000000..975a1efa164002
--- /dev/null
+++ b/tensorflow/security/fuzzing/arg_def_case_fuzz.cc
@@ -0,0 +1,44 @@
+/* Copyright 2020 The TensorFlow Authors. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
+#include <cstdint>
+#include <cstdlib>
+
+#include "tensorflow/core/platform/str_util.h"
+#include "tensorflow/core/platform/stringpiece.h"
+
+// This is a fuzzer for tensorflow::str_util::ArgDefCase
+
+namespace {
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  uint8_t *byte_data = const_cast<uint8_t *>(data);
+  char *char_data = reinterpret_cast<char *>(byte_data);
+
+  tensorflow::StringPiece sp(char_data, size);
+
+  tensorflow::str_util::ArgDefCase(sp);
+  for (const auto &c : sp) {
+    const bool is_letter = 'a' <= c && c <= 'z';
+    const bool is_digit = '0' <= c && c <= '9';
+    if (!is_letter && !is_digit) {
+      printf("Got '%c'\n", c);
+      assert(c == '_');
+    }
+  }
+
+  return 0;
+}
+
+}  // namespace
diff --git a/tensorflow/security/fuzzing/consume_leading_digits_fuzz.cc b/tensorflow/security/fuzzing/consume_leading_digits_fuzz.cc
new file mode 100644
index 00000000000000..d49bc1f21106e8
--- /dev/null
+++ b/tensorflow/security/fuzzing/consume_leading_digits_fuzz.cc
@@ -0,0 +1,41 @@
+/* Copyright 2020 The TensorFlow Authors. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
+#include <cstdint>
+#include <cstdlib>
+
+#include "tensorflow/core/platform/str_util.h"
+#include "tensorflow/core/platform/stringpiece.h"
+
+// This is a fuzzer for tensorflow::str_util::ConsumeLeadingDigits
+
+namespace {
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  uint8_t *byte_data = const_cast<uint8_t *>(data);
+  char *char_data = reinterpret_cast<char *>(byte_data);
+
+  tensorflow::StringPiece sp(char_data, size);
+  tensorflow::uint64 val;
+
+  const bool leading_digits =
+      tensorflow::str_util::ConsumeLeadingDigits(&sp, &val);
+  if (leading_digits) {
+    assert(val >= 0);
+  }
+
+  return 0;
+}
+
+}  // namespace
diff --git a/tensorflow/security/fuzzing/consume_non_whitespace_fuzz.cc b/tensorflow/security/fuzzing/consume_non_whitespace_fuzz.cc
new file mode 100644
index 00000000000000..6d2b5b929b8a68
--- /dev/null
+++ b/tensorflow/security/fuzzing/consume_non_whitespace_fuzz.cc
@@ -0,0 +1,51 @@
+/* Copyright 2020 The TensorFlow Authors. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
+#include <cstdint>
+#include <cstdlib>
+
+#include "tensorflow/core/platform/str_util.h"
+#include "tensorflow/core/platform/stringpiece.h"
+
+// This is a fuzzer for tensorflow::str_util::ConsumeNonWhitespace
+
+namespace {
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  uint8_t *byte_data = const_cast<uint8_t *>(data);
+  char *char_data = reinterpret_cast<char *>(byte_data);
+
+  tensorflow::StringPiece sp(char_data, size);
+  tensorflow::StringPiece spe;
+
+  while (!sp.empty()) {
+    const size_t initial_size = sp.size();
+    (void)initial_size;  // "use" initial_size even if assert is disabled
+
+    const bool leading_whitespace =
+        tensorflow::str_util::ConsumeNonWhitespace(&sp, &spe);
+
+    if (leading_whitespace) {
+      assert(!spe.empty());
+    }
+    assert(initial_size == (sp.size() + spe.size()));
+
+    tensorflow::str_util::RemoveLeadingWhitespace(&sp);
+    assert(initial_size > sp.size());
+  }
+
+  return 0;
+}
+
+}  // namespace
diff --git a/tensorflow/security/fuzzing/string_replace_fuzz.cc b/tensorflow/security/fuzzing/string_replace_fuzz.cc
new file mode 100644
index 00000000000000..fe43b9b78aa3d8
--- /dev/null
+++ b/tensorflow/security/fuzzing/string_replace_fuzz.cc
@@ -0,0 +1,48 @@
+/* Copyright 2020 The TensorFlow Authors. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+==============================================================================*/
+#include <fuzzer/FuzzedDataProvider.h>
+
+#include <cstdint>
+#include <cstdlib>
+
+#include "tensorflow/core/platform/str_util.h"
+#include "tensorflow/core/platform/stringpiece.h"
+
+// This is a fuzzer for tensorflow::str_util::StringReplace
+
+namespace {
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+  FuzzedDataProvider fuzzed_data(data, size);
+
+  if (size < 1) return 0;
+
+  bool all_flag = fuzzed_data.ConsumeBool();
+
+  std::string s = fuzzed_data.ConsumeRandomLengthString(10);
+  std::string oldsub = fuzzed_data.ConsumeRandomLengthString(5);
+  std::string newsub = fuzzed_data.ConsumeRemainingBytesAsString();
+
+  tensorflow::StringPiece sp(s);
+  tensorflow::StringPiece oldsubp(oldsub);
+  tensorflow::StringPiece newsubp(newsub);
+
+  std::string subbed =
+      tensorflow::str_util::StringReplace(sp, oldsubp, newsubp, all_flag);
+
+  return 0;
+}
+
+}  // namespace