Phase: Implementation Strategy: Input Validation Assume all input is malicious. Use an "accept known good" input
validation strategy, i.e., use a whitelist of acceptable inputs that
strictly conform to specifications. Reject any input that does not
strictly conform to specifications, or transform it into something that
does. When performing input validation, consider all potentially relevant
properties, including length, type of input, the full range of
acceptable values, missing or extra inputs, syntax, consistency across
related fields, and conformance to business rules. As an example of
business rule logic, "boat" may be syntactically valid because it only
contains alphanumeric characters, but it is not valid if the input is
only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs
(i.e., do not rely on a blacklist). A blacklist is likely to miss at
least one undesirable input, especially if the code's environment
changes. This can give attackers enough room to bypass the intended
validation. However, blacklists can be useful for detecting potential
attacks or determining which inputs are so malformed that they should be
rejected outright. |
Phase: Implementation Strategy: Output Encoding While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict whitelist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88). |
Description
