426
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
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 allowlist (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).
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-2000-0116 Extra "<" in front of SCRIPT tag bypasses XSS prevention.
https://www.cve.org/CVERecord?id=CVE-2000-0116
CVE-2001-1157 Extra "<" in front of SCRIPT tag.
https://www.cve.org/CVERecord?id=CVE-2001-1157
CVE-2002-2086 "<script" - probably a cleansing error
https://www.cve.org/CVERecord?id=CVE-2002-2086
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.
Nature Type ID Name Page
MemberOf 722 OWASP Top Ten 2004 Category A1 - Unvalidated Input 711 2334
MemberOf 992 SFP Secondary Cluster: Faulty Input Transformation 888 2416
MemberOf 1407 Comprehensive Categorization: Improper Neutralization 1400 2532
Taxonomy Mappings
Mapped Taxonomy Name Node ID Fit Mapped Node Name
PLOVER Extra Special Element
CWE-168: Improper Handling of Inconsistent Special Elements
Weakness ID : 168
CWE Version 4.14
CWE-168: Improper Handling of Inconsistent Special Elements
CWE-168: Improper Handling of Inconsistent Special Elements