CVE-2021-29434

Workarounds

For sites that cannot easily upgrade to a current supported version, the vulnerability can be patched by adding the following code to a wagtail_hooks.py module in any installed app:

from draftjs_exporter.dom import DOM
from wagtail.admin.rich_text.converters.html_to_contentstate import ExternalLinkElementHandler, PageLinkElementHandler
from wagtail.core import hooks
from wagtail.core.whitelist import check_url


def link_entity(props):
    id_ = props.get('id')
    link_props = {}

    if id_ is not None:
        link_props['linktype'] = 'page'
        link_props['id'] = id_
    else:
        link_props['href'] = check_url(props.get('url'))

    return DOM.create_element('a', link_props, props['children'])


@hooks.register('register_rich_text_features', order=1)
def register_link(features):
    features.register_converter_rule('contentstate', 'link', {
        'from_database_format': {
            'a[href]': ExternalLinkElementHandler('LINK'),
            'a[linktype="page"]': PageLinkElementHandler('LINK'),
        },
        'to_database_format': {
            'entity_decorators': {'LINK': link_entity}
        }
    })

Acknowledgements

Many thanks to Kevin Breen for reporting this issue.

For more information

If you have any questions or comments about this advisory:

• Visit Wagtail's support channels
• Email us at [email protected] (if you wish to send encrypted email, the public key ID is 0x6ba1e1a86e0f8ce8)

When saving the contents of a rich text field in the admin interface, Wagtail does not apply server-side checks to ensure that link URLs use a valid protocol. A malicious user with access to the admin interface could thus craft a POST request to publish content with javascript: URLs containing arbitrary code. The vulnerability is not exploitable by an ordinary site visitor without access to the Wagtail admin.

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2021-29434 has a CVSS score of 6.1 (High). The vector is network-reachable, high privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.12.4, 2.11.7); upgrading removes the vulnerable code path.

Kodem intelligence

Patched versions have been released as Wagtail 2.11.7 (for the LTS 2.11 branch) and Wagtail 2.12.4 (for the current 2.12 branch).

1. What is CVE-2021-29434? CVE-2021-29434 is a high-severity cross-site scripting (XSS) vulnerability in wagtail (pip), affecting versions >= 2.12, <= 2.12.3. It is fixed in 2.12.4, 2.11.7. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2021-29434? CVE-2021-29434 has a CVSS score of 6.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of wagtail are affected by CVE-2021-29434? wagtail (pip) versions >= 2.12, <= 2.12.3 is affected.
4. Is there a fix for CVE-2021-29434? Yes. CVE-2021-29434 is fixed in 2.12.4, 2.11.7. Upgrade to this version or later.
5. Is CVE-2021-29434 exploitable, and should I be worried? Whether CVE-2021-29434 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2021-29434 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2021-29434?
   • Upgrade wagtail to 2.12.4 or later
   • Upgrade wagtail to 2.11.7 or later