XSS protection mechanism only checks for sequences
with an alphabetical character following a (<), so a non-alphabetical
or null character (%00) following a < may be processed.
Developers should anticipate that null characters or null bytes will
be injected/removed/manipulated in the input vectors of their software
system. Use an appropriate combination of black lists and white lists to
ensure only valid, expected and appropriate input is processed by the
system.
Architecture and Design
Assume all input is malicious. Use a standard input validation
mechanism to validate all input for length, type, syntax, and business
rules before accepting the data to be displayed or stored. Use an
"accept known good" validation strategy.
Use and specify a strong output encoding (such as ISO 8859-1 or UTF
8).
Do not rely exclusively on blacklist validation to detect malicious
input or to encode output. There are too many variants to encode a
character; you're likely to miss some variants.
Inputs should be decoded and canonicalized to the application's
current internal representation before being validated. Make sure that
your application does not decode the same input twice. Such errors could
be used to bypass whitelist schemes by introducing dangerous inputs
after they have been checked.
Description
