GHSA-p2ch-c2c3-4xm5: CSRF
Impact
Affected versions of Winter CMS allow a backend AJAX handler to be invoked by a plain top-level GET navigation with no CSRF token. Backend\Classes\Controller::actionExists() accepted any public method on a controller as a page action, so handler-shaped names were never reserved from URL dispatch: an authenticated and authorized request to /backend/system/eventlogs/indexonEmptyLog reached the handler of the same name and truncated the system event log. Backend paths are routed through Route::any, and CSRF validation is skipped for HEAD, GET and OPTIONS requests.
The default SameSite=Lax session cookie is sent on top-level cross-site navigation, so a link on an attacker-controlled page is sufficient — no form, no script and no token. Handler arguments are taken from URL path segments, so the attacker also chooses the target record. Affected handlers across the backend, cms and system modules cover log truncation, resetting settings to their defaults, altering backend user state, and deleting CMS templates. None of them disclose data to the attacker or write attacker-controlled content, so the impact is destructive and state-changing rather than confidential.
To actively exploit this issue, an attacker would need no account of their own, but would need an authenticated backend user holding the relevant permission to follow an attacker-supplied link. The permissions guarding the affected handlers, system.accesslogs included, are by default assigned only to the built-in Developer role.
Patches
Page-action dispatch is now restricted to all-lowercase method names, which reserves handler-shaped names (onFoo, indexonFoo) from being reached by URL. AJAX dispatch is unchanged: handlers continue to work over POST with the X-WINTER-REQUEST-HANDLER header exactly as before, and need no changes.
IMPORTANT: This fix includes a breaking change to backend action routing. A public controller method used as a page action must now be named in lowercase — comingsoon() rather than comingSoon() — and dashed URLs are normalised to snakecase, so /coming-soon now resolves to comingsoon() instead of comingSoon(). Plugins with a camelCase page action should rename the method and its view file to match; the published URL does not need to change. Core is unaffected, and a survey of the plugin ecosystem found the change affects only a small number of plugins.
This security issue has been fixed in v1.2.14.
Workarounds
If you cannot upgrade, apply https://github.com/wintercms/winter/commit/353b23804dee2acf49fca996c72637040446824f manually.
As an interim mitigation, set 'samesite' => 'strict' in config/session.php. A strict session cookie is not sent on cross-site top-level navigation, which prevents the victim's session accompanying an attacker's link. Review this against any single sign-on or inbound-link flows into your backend first, as it also affects legitimate cross-site entry.
References
Credit to Awwader (@NRAwwad) 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 353b23804dee2acf49fca996c72637040446824f - Configuration
Set 'same_site' => 'strict' in config/session.php as an interim mitigation if you cannot upgrade to v1.2.14.
Winter CMS session configuration 'same_site' in config/session.php = 'strict' - Configuration
Update affected backend public controller page-action methods to all-lowercase names (e.g., coming_soon() instead of comingSoon()). Dashed URLs are normalised to snake_case (e.g., /coming-soon resolves to coming_soon() ).
Winter CMS backend page-action routing public controller method naming for page actions = all-lowercase (e.g., coming_soon() not comingSoon())
Event History
Frequently Asked Questions
Who can be targeted by this issue?
An attacker must cause an authenticated and authorized Winter CMS backend user to follow a top-level cross-site link. The default SameSite=Lax session cookie is sent with that navigation, so no form, script, or CSRF token is needed.
Is a default configuration affected?
Yes. The default SameSite=Lax session-cookie behavior permits the cross-site top-level GET navigation used in this attack, and backend routes accept GET requests while skipping CSRF validation for GET, HEAD, and OPTIONS.
What actions can an attacker trigger?
Affected handlers in the backend, cms, and system modules can truncate event logs, reset settings to defaults, alter backend-user state, and delete CMS templates. URL path segments supply handler arguments, allowing the attacker to select the target record where applicable.
Does exploitation expose data or allow content injection?
No. The described affected handlers do not disclose data to the attacker and do not write attacker-controlled content; the impact is destructive or state-changing.
How can I tell whether a request was exploited?
The data does not provide a definitive detection method. Review backend state for unexpected event-log truncation, settings resets, backend-user changes, or CMS template deletions.