399
Strategy = Input Validation
Developers should anticipate that macro symbols will be injected/removed/manipulated in the
input vectors of their product. Use an appropriate combination of denylists and allowlists to
ensure only valid, expected and appropriate input is processed by the system.
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.
Observed Examples
Reference Description
CVE-2002-0770 Server trusts client to expand macros, allows macro characters to be
expanded to trigger resultant information exposure.
https://www.cve.org/CVERecord?id=CVE-2002-0770
CVE-2008-2018 Attacker can obtain sensitive information from a database by using a comment
containing a macro, which inserts the data during expansion.
https://www.cve.org/CVERecord?id=CVE-2008-2018
MemberOf Relationships
This MemberOf relationships table shows additional CWE Catgeories and Views that reference this
weakness as a member. This information is often useful in understanding where a weakness fits
within the context of external information sources.
CWE Version 4.14
CWE-153: Improper Neutralization of Substitution Characters
CWE-153: Improper Neutralization of Substitution Characters