CAPEC-247 - Cross-Site Scripting with Masking through Invalid Characters in Identifiers

The attacker inserts invalid characters in identifiers to bypass application filtering of input. Filters may not scan beyond invalid characters but during later stages of processing content that follows these invalid characters may still be processed. This allows the attacker to sneak prohibited commands past filters and perform normally prohibited operations. Invalid characters may include null, carriage return, line feed or tab in an identifier. Successful bypassing of the filter can result in a XSS attack, resulting in the disclosure of web cookies or possibly other results.

Severity

Likelihood

Confidentiality

Integrity

Availability

The target must fail to remove invalid characters from input and fail to adequately scan beyond these characters.

No special resources are required.

Design: Use libraries and templates that minimize unfiltered input.

Implementation: Normalize, filter and white list any input that will be included in any subsequent web pages or back end operations.

Implementation: The victim should configure the browser to minimize active content from untrusted sources.