Malicious Data and Computer Security

Traditionally, computer security has focused on containing the effects of malicious users or malicious programs. However, as programs become more complex, an additional threat arises: malicious data. This threat arises because apparently benign programs can be made malicious, or subverted, by introduction of an attacker’s data—data that is interpreted as instructions by the program to perform activities that the computer’s operator would find undesirable. A variety of software features, some intentional and some unwitting, combine to create a software environment that is highly vulnerable to malicious data. This paper catalogs those features, discusses their effects, and examines potential countermeasures. In general, the outlook is depressing: as the economic incentives increase, these vulnerabilities are likely to be exploited more frequently; yet effective countermeasures are costly and complex.