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This rule complements rule SER12-J. Prevent deserialization of untrusted classes. Whereas SER12-J requires the programmer to ensure the absence of classes that might perform dangerous operations by validating data before deserializing it, SER13-J requires that all serializable classes refrain, by default, from performing dangerous operations during deserialization. SER12-J and SER13-J both guard against the same class of deserialization vulnerabilities. Theoretically, a given system is secure against this class of vulnerabilities if either (1) all deployed code on that system follows SER12-J or (2) all deployed code on that system follows SER13-J. However, because much existing code violates both of these rules, the CERT Coding Standard takes the "belt and suspenders" approach and requires compliant code to follow both rules.
For the purposes of complying compliance with SER13-J, it is permitted to assume that, if an ObjectInputStream contains a whitelist, then control will pass to the readObject or readResolve method () or readResolve() method of a class C only if C is on the whitelist. In other words, class C does a class does not need to check that it appears on the whitelist; it only needs to check that a whitelist exists. This eliminates the need to perform a redundant check against the whitelist, and it enables compatibility with a greater range of whitelist implementations.
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