diff --git a/cpp/src/gandiva/gdv_function_stubs.cc b/cpp/src/gandiva/gdv_function_stubs.cc
index 6b3e9935b017..c9d9e5d5ca58 100644
--- a/cpp/src/gandiva/gdv_function_stubs.cc
+++ b/cpp/src/gandiva/gdv_function_stubs.cc
@@ -28,6 +28,7 @@
 #include "arrow/util/base64.h"
 #include "arrow/util/bit_util.h"
 #include "arrow/util/double_conversion_internal.h"
+#include "arrow/util/int_util_overflow.h"
 #include "arrow/util/value_parsing.h"
 
 #include "gandiva/encrypt_utils.h"
@@ -663,8 +664,14 @@ const char* mask_utf8_utf8_utf8_utf8(int64_t context, const char* data, int32_t
     return nullptr;
   }
 
-  int32_t max_length =
-      std::max(upper_length, std::max(lower_length, num_length)) * data_len;
+  int32_t max_length;
+  if (ARROW_PREDICT_FALSE(arrow::internal::MultiplyWithOverflow(
+          std::max(upper_length, std::max(lower_length, num_length)), data_len,
+          &max_length))) {
+    gdv_fn_context_set_error_msg(context, "Could not allocate memory for output string");
+    *out_len = 0;
+    return nullptr;
+  }
   char* out = reinterpret_cast<char*>(gdv_fn_context_arena_malloc(context, max_length));
   if (out == nullptr) {
     gdv_fn_context_set_error_msg(context, "Could not allocate memory for output string");
diff --git a/cpp/src/gandiva/gdv_function_stubs_test.cc b/cpp/src/gandiva/gdv_function_stubs_test.cc
index c0197eb815c8..a85370fdc7fb 100644
--- a/cpp/src/gandiva/gdv_function_stubs_test.cc
+++ b/cpp/src/gandiva/gdv_function_stubs_test.cc
@@ -805,7 +805,7 @@ TEST(TestGdvFnStubs, TestInitCap) {
   EXPECT_EQ(std::string(out_str, out_len), "{Õhp,Pqśv}Ń+");
   EXPECT_FALSE(ctx.has_error());
 
-  out_str = gdv_fn_initcap_utf8(ctx_ptr, "sɦasasdsɦsd\"sdsdɦ", 19, &out_len);
+  out_str = gdv_fn_initcap_utf8(ctx_ptr, "sɦasasdsɦsd\"sdsdɦ", 20, &out_len);
   EXPECT_EQ(std::string(out_str, out_len), "Sɦasasdsɦsd\"Sdsdɦ");
   EXPECT_FALSE(ctx.has_error());
 
@@ -1188,6 +1188,44 @@ TEST(TestGdvFnStubs, TestMaskTruncatedUtf8NoOverread) {
   EXPECT_TRUE(ctx.has_error());
 }
 
+TEST(TestGdvFnStubs, TestMaskOutputLengthOverflow) {
+  gandiva::ExecutionContext ctx;
+  auto ctx_ptr = reinterpret_cast<int64_t>(&ctx);
+  int32_t out_len = -1;
+  const std::string data(65536, 'A');
+  const std::string replacement(65536, 'X');
+  auto result = mask_utf8_utf8_utf8_utf8(
+      ctx_ptr, data.data(), static_cast<int32_t>(data.size()), replacement.data(),
+      static_cast<int32_t>(replacement.size()), "x", 1, "n", 1, &out_len);
+  EXPECT_EQ(result, nullptr);
+  EXPECT_EQ(out_len, 0);
+  EXPECT_TRUE(ctx.has_error());
+}
+
+TEST(TestGdvFnStubs, TestCaseConversionTruncatedUtf8) {
+  const std::string inputs[] = {"a\xc2\xa2", "a\xe2\x82\xac", "a\xf0\x9f\x98\x80"};
+  for (auto convert : {gdv_fn_lower_utf8, gdv_fn_upper_utf8, gdv_fn_initcap_utf8}) {
+    for (const auto& input : inputs) {
+      const auto full_len = static_cast<int32_t>(input.size());
+      for (int32_t len = 2; len < full_len; ++len) {
+        gandiva::ExecutionContext ctx;
+        auto ctx_ptr = reinterpret_cast<int64_t>(&ctx);
+        int32_t out_len = -1;
+        // Bytes beyond len complete the glyph, but are outside the input slice.
+        convert(ctx_ptr, input.data(), len, &out_len);
+        EXPECT_EQ(out_len, 0);
+        EXPECT_TRUE(ctx.has_error());
+      }
+      gandiva::ExecutionContext ctx;
+      auto ctx_ptr = reinterpret_cast<int64_t>(&ctx);
+      int32_t out_len = -1;
+      convert(ctx_ptr, input.data(), full_len, &out_len);
+      EXPECT_GT(out_len, 0);
+      EXPECT_FALSE(ctx.has_error());
+    }
+  }
+}
+
 TEST(TestGdvFnStubs, TestTranslate) {
   gandiva::ExecutionContext ctx;
   int64_t ctx_ptr = reinterpret_cast<int64_t>(&ctx);
diff --git a/cpp/src/gandiva/gdv_string_function_stubs.cc b/cpp/src/gandiva/gdv_string_function_stubs.cc
index 55f5f13ac312..fc18bc0fac01 100644
--- a/cpp/src/gandiva/gdv_string_function_stubs.cc
+++ b/cpp/src/gandiva/gdv_string_function_stubs.cc
@@ -289,6 +289,14 @@ const char* gdv_fn_lower_utf8(int64_t context, const char* data, int32_t data_le
     }
 
     // Control reaches here when we encounter a multibyte character
+    // Ensure the multibyte sequence fits within the buffer to avoid
+    // reading past data_len (truncated trailing multibyte sequence).
+    if (char_len > data_len - i) {
+      gdv_fn_set_error_for_invalid_utf8(context, data[i]);
+      *out_len = 0;
+      return "";
+    }
+
     const auto* in_char = (const uint8_t*)(data + i);
 
     // Decode the multibyte character
@@ -366,6 +374,14 @@ const char* gdv_fn_upper_utf8(int64_t context, const char* data, int32_t data_le
     }
 
     // Control reaches here when we encounter a multibyte character
+    // Ensure the multibyte sequence fits within the buffer to avoid
+    // reading past data_len (truncated trailing multibyte sequence).
+    if (char_len > data_len - i) {
+      gdv_fn_set_error_for_invalid_utf8(context, data[i]);
+      *out_len = 0;
+      return "";
+    }
+
     const auto* in_char = (const uint8_t*)(data + i);
 
     // Decode the multibyte character
@@ -584,6 +600,14 @@ const char* gdv_fn_initcap_utf8(int64_t context, const char* data, int32_t data_
     char_len = gdv_fn_utf8_char_length(data[i]);
 
     // Control reaches here when we encounter a multibyte character
+    // Ensure the multibyte sequence fits within the buffer to avoid
+    // reading past data_len (truncated trailing multibyte sequence).
+    if (char_len > data_len - i) {
+      gdv_fn_set_error_for_invalid_utf8(context, data[i]);
+      *out_len = 0;
+      return "";
+    }
+
     const auto* in_char = (const uint8_t*)(data + i);
 
     // Decode the multibyte character