290
with "sinks" (destinations where the data interacts with external components, a lower layer such
as the OS, etc.)
Effectiveness = High
Potential Mitigations
Phase: Implementation
Strategy = Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use
a list 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. This 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, denylists 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
Use and specify an output encoding that can be handled by the downstream component that
is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an
encoding is not specified, a downstream component may choose a different encoding, either
by assuming a default encoding or automatically inferring which encoding is being used, which
can be erroneous. When the encodings are inconsistent, the downstream component might
treat some character or byte sequences as special, even if they are not special in the original
encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks;
they even might be able to bypass protection mechanisms that assume the original encoding is
also being used by the downstream component.
Phase: Implementation
Strategy = Input Validation
Inputs should be decoded and canonicalized to the application's current internal representation
before being validated (CWE-180). Make sure that the application does not decode the same
input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by
introducing dangerous inputs after they have been checked.
Demonstrative Examples
Example 1:
The following web application code attempts to read an integer value from a request object. If the
parseInt call fails, then the input is logged with an error message indicating what happened.
Example Language: Java (Bad)
String val = request.getParameter("val");
try {
int value = Integer.parseInt(val);
}
catch (NumberFormatException) {
log.info("Failed to parse val = " + val);
}
...
CWE Version 4.14
CWE-117: Improper Output Neutralization for Logs
CWE-117: Improper Output Neutralization for Logs