GHSA-7mpf-4465-7fc2: XSS
Impact
Backend\Widgets\Lists::evalImageTypeValue() interpolated the resolved image URL into a single-quoted src attribute without escaping it. Where a list column of type image rendered an attacker-influenced value, that value could break out of the attribute and inject arbitrary attributes — including event handlers — into the backend list, executing in the session of whichever backend user viewed it.
Winter core ships no image list column, so a default installation is unaffected. Exploitation requires a plugin that renders attacker-influenced values through one.
The supported image sources are plugins, themes, the Media Library, the uploads directory, and Attach\File models; an arbitrary external URL is not among them. ImageResizer::filterGetUrl() returns the value it was given when it cannot resolve an image, however, so an unsupported value reached the attribute verbatim rather than being rejected.
As with previous issues of this kind the severity is limited: an attacker must already be able to store the value, and a backend user must then open the affected list. Note that validating a stored URL was not necessarily sufficient — a payload can survive filtervar($url, FILTERVALIDATEURL), since / is valid both in a URL path and after a quoted HTML attribute value.
Patches
evalImageTypeValue() now escapes the image URL, along with the width and height taken from the column configuration, before interpolating them into the tag.
This security issue has been fixed as of v1.2.14 (commit 0941c9816181095fe35d58e78e6d0c4a49238967).
Workarounds
Apply the commit above to modules/backend/widgets/Lists.php manually if you are unable to upgrade to v1.2.14.
References
- https://github.com/wintercms/winter/security/advisories/GHSA-43w4-4j3c-jx29 - https://github.com/wintercms/winter/commit/0941c9816181095fe35d58e78e6d0c4a49238967
Credit to Seungyeon Park (@sy460129) for reporting the issue.
For more information
If you have any questions or comments about this advisory: - Email us at hello@wintercms.com
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
composer/winter/wn-backend-moduleto a version that resolves this vulnerability.Fixed in 1.2.14 - Upgrade
Upgrade
wintercms/winterto a version that resolves this vulnerability.Fixed in v1.2.14Patch 0941c9816181095fe35d58e78e6d0c4a49238967 - Configuration
Apply commit 0941c9816181095fe35d58e78e6d0c4a49238967 manually to modules/backend/widgets/Lists.php if you are unable to upgrade to v1.2.14, ensuring evalImageTypeValue() escapes the image URL (and width/height from the column configuration) before building the <img> tag.
modules/backend/widgets/Lists.php (Backend\Widgets\Lists::evalImageTypeValue) escape resolved image URL before interpolating into single-quoted src attribute = escaped
Event History
Frequently Asked Questions
Are default Winter CMS installations affected?
No. Winter core ships no image list column, so a default installation is unaffected. Exposure requires a plugin that renders attacker-influenced values in a backend list column of type image.
What must an attacker be able to do to exploit this?
They must already be able to store a value that is rendered through an affected image list column, and a backend user must view the resulting list. The injected attributes can then execute in the viewing backend user's session.
Can an arbitrary external image URL trigger the issue?
Arbitrary external URLs are not supported image sources. However, if an unsupported value reaches the image attribute, ImageResizer::filterGetUrl() returns it verbatim when it cannot resolve it rather than rejecting it.
How can I determine whether my deployment is exposed?
Review installed plugins for backend list columns configured with type image, then identify whether values displayed by those columns can be influenced by untrusted users. Relevant image sources include plugins, themes, the Media Library, the uploads directory, and Attach\File models.