Fix: validate byte count in file_message.py decode handlers - #2980
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janiversen merged 6 commits intoJul 24, 2026
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Adds bounds checking to ReadFileRecordRequest, WriteFileRecordRequest, and ReadFifoQueueResponse decode handlers, consistent with pymodbus-dev#2974 and pymodbus-dev#2977. Raises ModbusException instead of struct.error when byte_count exceeds actual payload length.
janiversen
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Jul 24, 2026
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Hi @janiversen, I have added three tests covering the new validation branches (test_read_file_record_request_decode_invalid_byte_count, test_write_file_record_request_decode_invalid_byte_count, test_read_fifo_queue_response_decode_invalid_count). All 16 CI checks are now passing with 100% coverage. Could you take another look when you get a chance? Thanks! |
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Thank you so much for your assistance :) |
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Adds bounds checking to three decode handlers in
pymodbus/pdu/file_message.py,consistent with the fixes applied in #2974 and #2977.
Changes:
ReadFileRecordRequest.decode: validatebyte_countagainstlen(data)before iteratingWriteFileRecordRequest.decode: validatebyte_countagainstlen(data)before loopingReadFifoQueueResponse.decode: validatecountagainstlen(data)before iteratingPreviously, an oversized
byte_countfield causedstruct.unpack()to raisestruct.error, which escaped theModbusException/ValueError/IndexErrorhandler in
DecodePDU.decode(). The fix raisesModbusExceptioninstead,matching the behaviour added in #2974 and #2977.
Related to security advisory GHSA-xxxx (private).