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[modbus] Fix buffer overflow in modbus (#14719)

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Co-authored-by: J. Nick Koston <nick@home-assistant.io>
This commit is contained in:
Adam DeMuri
2026-03-11 22:00:26 -10:00
committed by GitHub
co-authored by J. Nick Koston
parent f8a22b87b8
commit 8a5f008aee
2 changed files with 65 additions and 6 deletions
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esphome/components/modbus/modbus.cpp
+6 -6
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@@ -125,13 +125,17 @@ bool Modbus::parse_modbus_byte_(uint8_t byte) {
// Byte 0: modbus address (match all)
if (at == 0)
return true;
uint8_t address = raw[0];
uint8_t function_code = raw[1];
// Byte 1: function code
if (at == 1)
return true;
// Byte 2: Size (with modbus rtu function code 4/3)
// See also https://en.wikipedia.org/wiki/Modbus
if (at == 2)
return true;
uint8_t address = raw[0];
uint8_t function_code = raw[1];
uint8_t data_len = raw[2];
uint8_t data_offset = 3;
@@ -146,10 +150,6 @@ bool Modbus::parse_modbus_byte_(uint8_t byte) {
// chance that this is a complete message ... admittedly there is a small chance is
// isn't but that is quite small given the purpose of the CRC in the first place
// Fewer than 2 bytes can't calc CRC
if (at < 2)
return true;
data_len = at - 2;
data_offset = 1;