COMMON WEAKNESS ENUMERATIONDraft

CWE-692

Incomplete Denylist to Cross-Site Scripting

The product uses a denylist-based protection mechanism to defend against XSS attacks, but the denylist is incomplete, allowing XSS variants to succeed.

Abstraction

Compound

Structure

Chain

Likelihood of Exploit

Medium

Understand the problem

What is the problem?

The product uses a denylist-based protection mechanism to defend against XSS attacks, but the denylist is incomplete, allowing XSS variants to succeed.

Extended description

While XSS might seem simple to prevent, web browsers vary so widely in how they parse web pages, that a denylist cannot keep track of all the variations. The "XSS Cheat Sheet" [REF-714] contains a large number of attacks that are intended to bypass incomplete denylists.

Root cause

How and when does the problem arise?

Lifecycle phase

Implementation

Risk

What does successful exploitation lead to?

Execute Unauthorized Code or Commands

Affected security scopes: Confidentiality, Integrity, Availability

Defence

How is it prevented and fixed?

  • Follow secure coding guidelines for input handling and boundary checking.
  • Enforce strict security reviews and automated static analysis (SAST) checks.