critical CVSS 9.9

CVE-2026-27591·PHP vulnerability

Winter is a free, open-source content management system (CMS) based on the Laravel PHP framework. Prior to 1.0.477, 1.1.12, and 1.2.12, Winter CMS allowed authenticated backend users to escalate their accounts level of access to the system by modifying the roles / permissions assigned to their account through specially crafted requests to the backend while logged in. To actively exploit this security issue, an attacker would need access to the Backend with a user account with any level of access. This vulnerability is fixed in 1.0.477, 1.1.12, and 1.2.12.

Severity
critical
Software
PHP
Fixed in
1.2.12
Published
2026-03-11

Affected versions

From: 1.2.0

Until: 1.2.12

Fixed in: 1.2.12

How to fix this CVE

Winter CMS users must immediately upgrade to version 1.2.12 or later to patch a critical privilege escalation vulnerability affecting the backend. Authenticated users with any level of backend access can exploit this flaw to illegally elevate their permissions by sending specially crafted requests. Review and audit all user accounts post-upgrade, especially those with elevated privileges, to ensure no unauthorized access modifications occurred.

sudo dnf check-update php && sudo dnf upgrade php

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST/PUT requests to backend endpoints containing role_id, permission_id, or role/permission modification parameters from authenticated sessions; look for rapid successive requests modifying account permissions or unexpected elevation of non-admin accounts to admin status in audit logs

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Implement a WAF rule to restrict POST/PUT requests to backend permission/role endpoints (`/backend/auth/roles`, `/backend/auth/permissions`) to only requests originating from whitelisted administrative IP ranges and requiring additional CSRF/token validation beyond standard session cookies

How to check if you are affected

  1. Run `php -v` to check the currently installed PHP version and confirm Winter CMS version via your application's version file or administration dashboard
  2. Verify Winter CMS installation by checking the `/config/app.php` or `composer.json` file to confirm the exact installed version is below 1.2.12
  3. Examine backend access logs (typically in `storage/logs/`) for unusual role or permission modification requests, particularly POST/PUT requests to permission or role endpoints from unexpected IP addresses or user accounts
  4. After upgrading to 1.2.12, confirm the patch by running `php -v` again and validating the Winter CMS version in the admin panel shows the updated release number

FAQ

What is CVE-2026-27591?

CVE-2026-27591 is a critical privilege escalation vulnerability in Winter CMS that allows authenticated backend users to arbitrarily modify their own role and permission assignments through manipulated backend requests, effectively granting themselves elevated system access without authorization.

Is CVE-2026-27591 being actively exploited?

As of the latest intelligence, CVE-2026-27591 is not listed in the CISA Known Exploited Vulnerabilities catalog and no public exploits are currently available, though the low barrier to exploitation makes immediate patching critical.

What versions of Winter CMS are affected by CVE-2026-27591?

Winter CMS versions 1.2.0 through 1.2.11 are vulnerable; versions 1.0.477, 1.1.12, and 1.2.12 or later contain the security patch.

How do I check if my server is vulnerable to CVE-2026-27591?

Navigate to the Winter CMS admin dashboard and check Settings > About to view your installation version. If it shows 1.2.0–1.2.11, your system is vulnerable and requires immediate upgrade to 1.2.12 or newer.

Does Defensia detect CVE-2026-27591?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If PHP with Winter CMS is installed on a monitored server, CVE-2026-27591 will appear in your dashboard with remediation steps.

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References

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