Final answer:
The property in the Bell-LaPadula model that says a subject may not read information at a higher security level than they possess is called the Simple Security Rule.
Step-by-step explanation:
The property in the Bell-LaPadula model that says a subject may not read information at a higher security level than they possess is called the Simple Security Rule. This rule ensures that information flows downwards in security levels, known as the 'no read up' principle.
It helps to prevent unauthorized access and maintain confidentiality. For example, if a subject has a security level of 'Secret', they cannot read information classified as 'Top Secret'.