From 2f7270cf8f6f069191920f81503466361e42515b Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Sun, 18 Jan 2026 18:36:32 -1000
Subject: [PATCH] [uart] Replace unsafe sprintf with buf_append_printf in
 debugger (#13288)

---
 esphome/components/uart/uart_debugger.cpp | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/esphome/components/uart/uart_debugger.cpp b/esphome/components/uart/uart_debugger.cpp
index b51a57d68e..5490154d01 100644
--- a/esphome/components/uart/uart_debugger.cpp
+++ b/esphome/components/uart/uart_debugger.cpp
@@ -107,7 +107,7 @@ void UARTDebug::log_hex(UARTDirection direction, std::vector<uint8_t> bytes, uin
     if (i > 0) {
       res += separator;
     }
-    sprintf(buf, "%02X", bytes[i]);
+    buf_append_printf(buf, sizeof(buf), 0, "%02X", bytes[i]);
     res += buf;
   }
   ESP_LOGD(TAG, "%s", res.c_str());
@@ -147,7 +147,7 @@ void UARTDebug::log_string(UARTDirection direction, std::vector<uint8_t> bytes)
     } else if (bytes[i] == 92) {
       res += "\\\\";
     } else if (bytes[i] < 32 || bytes[i] > 127) {
-      sprintf(buf, "\\x%02X", bytes[i]);
+      buf_append_printf(buf, sizeof(buf), 0, "\\x%02X", bytes[i]);
       res += buf;
     } else {
       res += bytes[i];
@@ -166,11 +166,13 @@ void UARTDebug::log_int(UARTDirection direction, std::vector<uint8_t> bytes, uin
   } else {
     res += ">>> ";
   }
+  char buf[4];  // max 3 digits for uint8_t (255) + null
   for (size_t i = 0; i < len; i++) {
     if (i > 0) {
       res += separator;
     }
-    res += to_string(bytes[i]);
+    buf_append_printf(buf, sizeof(buf), 0, "%u", bytes[i]);
+    res += buf;
   }
   ESP_LOGD(TAG, "%s", res.c_str());
   delay(10);
@@ -189,7 +191,7 @@ void UARTDebug::log_binary(UARTDirection direction, std::vector<uint8_t> bytes,
     if (i > 0) {
       res += separator;
     }
-    sprintf(buf, "0b" BYTE_TO_BINARY_PATTERN " (0x%02X)", BYTE_TO_BINARY(bytes[i]), bytes[i]);
+    buf_append_printf(buf, sizeof(buf), 0, "0b" BYTE_TO_BINARY_PATTERN " (0x%02X)", BYTE_TO_BINARY(bytes[i]), bytes[i]);
     res += buf;
   }
   ESP_LOGD(TAG, "%s", res.c_str());