Incorrect or incomplete emulation can introduce vulnerability.
In general, an emulation fidelity vulnerability exists when
a system must emulate another system or device,
that emulation is incorrect or incomplete, and
the system uses the emulated state information to make security decisions.
The defect might be some or all of the following:
Emulation that is too abstract. Many network-based intrusion detection systems passively watch traffic of other systems, trying to guess the state of end nodes in communications with one another based on communication fragments. Packet-based firewalls in certain configurations exhibit this same shortcoming. For both of these examples, complete emulation is not generally possible because many end-node policies that influence their state are not observable in the traffic.
The emulator is simply wrong (i.e., logic error) and does not emulate the original correctly.
The eumlation is correct, but it does not perform in realtime. That is, it cannot keep up with what it's emulating, resulting in a denial of service.
Hoglund, Greg & McGraw, Gary. Exploiting Software: How to Break Code. Boston, MA: Addison-Wesley, 2004.
Finlay, Ian. Vulnerability Note VU#548515: Multiple intrusion detection systems may be circumvented via %u encoding. http://www.kb.cert.org/vuls/id/548515 (2003).
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