Improper Neutralization of Alternate XSS Syntax
The product does not neutralize or incorrectly neutralizes user-controlled input for alternate script syntax.
The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.
Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.
In the following example, an XSS neutralization method intends to replace script tags in user-supplied input with a safe equivalent:
The code only works when the "script" tag is in all lower-case, forming an incomplete denylist (CWE-184). Equivalent tags such as "SCRIPT" or "ScRiPt" will not be neutralized by this method, allowing an XSS attack.
Weaknesses in this category are related to the A03 category "Injection" in the OWASP Top Ten 2021.
This category identifies Software Fault Patterns (SFPs) within the Tainted Input to Command cluster (SFP24).
This view (slice) covers all the elements in CWE.
This view (slice) lists weaknesses that can be introduced during implementation.