CVE-2020-15118 Cross-Site Scripting in Wagtail

Medium 5.7 Published 20 Jul 2020 Updated 4 Aug 2024

Wagtail editors can inject HTML into form help text, leading to cross-site scripting and potential privilege escalation for site visitors.

Exploited in the wild: Not known
Login needed: An administrator
Attackable: Over the internet
Victim action needed: A user has to click or open something
Fix: Available

What is CVE-2020-15118?

CVE-2020-15118 is a medium-severity cross-site scripting vulnerability in wagtail, published on 20 Jul 2020. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.

Official description

In Wagtail before versions 2.7.4 and 2.9.3, when a form page type is made available to Wagtail editors through the `wagtail.contrib.forms` app, and the page template is built using Django's standard form rendering helpers such as form.as_p, any HTML tags used within a form field's help text will be rendered unescaped in the page. Allowing HTML within help text is an intentional design decision by Django; however, as a matter of policy Wagtail does not allow editors to insert arbitrary HTML by default, as this could potentially be used to carry out cross-site scripting attacks, including privilege escalation. This functionality should therefore not have been made available to editor-level users. The vulnerability is not exploitable by an ordinary site visitor without access to the Wagtail admin. Patched versions have been released as Wagtail 2.7.4 (for the LTS 2.7 branch) and Wagtail 2.9.3 (for the current 2.9 branch). In these versions, help text will be escaped to prevent the inclusion of HTML tags. Site owners who wish to re-enable the use of HTML within help text (and are willing to accept the risk of this being exploited by editors) may set WAGTAILFORMS_HELP_TEXT_ALLOW_HTML = True in their configuration settings. Site owners who are unable to upgrade to the new versions can secure their form page templates by rendering forms field-by-field as per Django's documentation, but omitting the |safe filter when outputting the help text.

Weakness: CWE-79

Which versions are affected by CVE-2020-15118?

5 open source packages ship an affected version, including wagtail. It affects 1 product.

Package	Affected	Fixed in
`wagtail` PyPI	All versions	`2.7.4`
`wagtail` PyPI	All versions	`2.7.4`
`wagtail` PyPI	From `2.7`	`2.7.4, 2.9.3`
`wagtail` PyPI	From `2.8rc1`	`2.9.3`
`wagtail` PyPI	From `2.8rc1`	`2.9.3`

Products include Torchbox Wagtail.

How do I fix CVE-2020-15118?

Upgrade wagtail to a fixed version for your release line: 2.7.4 or 2.9.3.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2020-15118 being exploited?

There is no known exploitation of CVE-2020-15118 in the wild and no public exploit code.

Sources

Also known as GHSA-2473-9hgq-j7xw, PYSEC-2020-154.