Package Instance

Craft CMS vulnerable to potential authenticated Remote Code Execution via Twig SSTI
For this to work, users must have administrator access to the Craft Control Panel, and [allowAdminChanges](https://craftcms.com/docs/5.x/reference/config/general.html#allowadminchanges) must be enabled for this to work, which is against Craft CMS' recommendations for any non-dev environment.

https://craftcms.com/knowledge-base/securing-craft#set-allowAdminChanges-to-false-in-production

Alternatively, a non-administrator account with allowAdminChanges disabled can be used, provided access to the System Messages utility is available.

It is possible to craft a malicious payload using the Twig `map` filter in text fields that accept Twig input under Settings in the Craft control panel or using the System Messages utility, which could lead to a RCE.

Users should update to the patched versions (5.8.21 and 4.16.17) to mitigate the issue.

References:

https://github.com/craftcms/cms/commit/d82680f4a05f9576883bb83c3f6243d33ca73ebe

https://github.com/craftcms/cms/blob/5.x/CHANGELOG.md#5821---2025-12-04

Craft CMS Vulnerable to Authenticated RCE via "craft.app.fs.write()" in Twig Templates
An authenticated administrator can achieve Remote Code Execution (RCE) by injecting a Server-Side Template Injection (SSTI) payload into Twig template fields (e.g., Email Templates). By calling the `craft.app.fs.write()` method, an attacker can write a malicious PHP script to a web-accessible directory and subsequently access it via the browser to execute arbitrary system commands.

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Craft CMS Vulnerable to SSRF in GraphQL Asset Mutation via Alternative IP Notation
The `saveAsset` GraphQL mutation uses `filter_var(..., FILTER_VALIDATE_IP)` to block a specific list of IP addresses. However, alternative IP notations (hexadecimal, mixed) are not recognized by this function, allowing attackers to bypass the blocklist and access cloud metadata services.

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Craft CMS vulnerable to potential information disclosure via unchecked asset relocation
Authenticated users on a Craft installation could potentially expose sensitive assets via their user profile photo via maliciously crafted requests.

Users should update to the patched versions (5.8.21 and 4.16.17) to mitigate the issue.

 Resources:

https://github.com/craftcms/cms/commit/4bcb0db554e273b66ce3b75263a13414c2368fc9

https://github.com/craftcms/cms/commit/4bcb0db554e273b66ce3b75263a13414c2368fc9

CraftCMS vulnerable to reflective XSS via incomplete return URL sanitization
The fix for CVE-2025-35939 in `craftcms/cms` introduced a `strip_tags()` call in `src/web/User.php` to sanitize return URLs before they are stored in the session. However, `strip_tags()` only removes HTML tags (angle brackets) -- it does not inspect or filter URL schemes. Payloads like `javascript:alert(document.cookie)` contain no HTML tags and pass through `strip_tags()` completely unmodified, enabling reflected XSS when the return URL is rendered in an `href` attribute.

Craft CMS has a potential information disclosure vulnerability in preview tokens
Craft CMS has a CSRF issue in the preview token endpoint at `/actions/preview/create-token`.  The endpoint accepts an attacker-supplied `previewToken`.

Because the action does not require POST and does not enforce a CSRF token, an attacker can force a logged-in victim editor to mint a preview token chosen by the attacker.

That token can then be used by the attacker (without authentication) to access previewed/unpublished content tied to the victim’s authorized preview scope.

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Craft CMS vulnerable to potential authenticated Remote Code Execution via malicious attached Behavior
This was reported as a vulnerability in Yii framework on August 7th (https://github.com/yiisoft/yii2/security/advisories/GHSA-gcmh-9pjj-7fp4). The Yii framework team denies responsibility for this (placing the onus on application developers) and hence has not (and seemingly will not) provide a fix at the framework level. Hence, I am reporting this to Craft as I found it to affect the latest (`5.6.0`) version of Craft CMS.

Leveraging a legitimate but maliciously crafted Yii `Behavior` class, it’s possible to trigger Remote Code Execution (RCE) via Reflection when the tainted `Behavior` is attached to a Yii `Component`, and an event is also fired on the tainted `Component`.

Craft CMS Vulnerable to Stored XSS via User Group Name in User Permissions Page
A stored XSS vulnerability exists in the User Permissions page. The User Group name is rendered without proper HTML escaping in the permissions section, allowing an attacker to execute arbitrary JavaScript when another user views or edits a user's permissions.

> [!NOTE]
> This is a separate vulnerability from the previously reported "[Stored XSS via User Group Name in User Settings Page](https://github.com/craftcms/cms/security/advisories/GHSA-2423-8xxj-wc3g)" and "[Multiple Stored XSS in User Group Edit Page](https://github.com/craftcms/cms/security/advisories/GHSA-vx7g-xw92-g4xj)". This affects a different sink: the individual user's permissions page.

Craft CMS Vulnerable to Stored XSS in Number Prefix & Suffix Fields
A stored XSS vulnerability exists in the Number field type settings. The Prefix and Suffix fields are rendered using the `|md|raw` Twig filter without proper escaping, allowing script execution when the Number field is displayed on users' profiles.

Craft CMS: GraphQL Asset Mutation Privilege Escalation
Type: Privilege Escalation (CWE-269)
Affected: Craft CMS 5.x (likely affects 4.x and 3.x as well)
Location: `src/gql/resolvers/mutations/Asset.php lines 57-107`