Affected: pallets jinja

Jinja is an extensible templating engine. Special placeholders in the template allow writing code similar to Python syntax. It is possible to inject arbitrary HTML attributes into the rendered HTML template, potentially leading to Cross-Site Scripting (XSS). The Jinja `xmlattr` filter can be abused to inject arbitrary HTML attribute keys and values, bypassing the auto escaping mechanism and potentially leading to XSS. It may also be possible to bypass attribute validation checks if they are blacklist-based.

Affected: PyPI: jinja2

The `xmlattr` filter in affected versions of Jinja accepts keys containing spaces. XML/HTML attributes cannot contain spaces, as each would then be interpreted as a separate attribute. If an application accepts keys (as opposed to only values) as user input, and renders these in pages that other users see as well, an attacker could use this to inject other attributes and perform XSS. Note that accepting keys as user input is not common or a particularly intended use case of the `xmlattr` filter, and an application doing so should already be verifying what keys are provided regardless of this fix.

Affected: PyPI: jinja2

The `xmlattr` filter in affected versions of Jinja accepts keys containing spaces. XML/HTML attributes cannot contain spaces, as each would then be interpreted as a separate attribute. If an application accepts keys (as opposed to only values) as user input, and renders these in pages that other users see as well, an attacker could use this to inject other attributes and perform XSS. Note that accepting keys as user input is not common or a particularly intended use case of the `xmlattr` filter, and an application doing so should already be verifying what keys are provided regardless of this fix.