Security Digest · Vulnerability record
CVE-2026-27591: Winter vulnerable to privilege escalation by authenticated backend users
Winter is a free, open-source content management system (CMS) based on the Laravel PHP framework.
CVSS 10.0 Critical EPSS 0.9% · p58
Should you act?
Critical, preconditions apply
Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.9%, percentile 58: FIRST’s model estimates a 0.9% chance of exploitation activity in the next 30 days, higher than 58% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Needs an account (low (any account)). Exposure depends on who can log in.
- Only applies if your dependency tree includes
winter/wn-backend-module(Composer (PHP)) >= 1.2.0, < 1.2.12, fixed in 1.2.12;winter/wn-backend-module(Composer (PHP)) >= 1.1.0, < 1.1.12, fixed in 1.1.12;winter/wn-backend-module(Composer (PHP)) < 1.0.477, fixed in 1.0.477. Check your lockfile, including transitive dependencies.
What it is
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.
From the GitHub advisory
Impact Affected versions of 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.
The Winter CMS maintainers strongly recommend that all Winter CMS sites that have any reliance on the roles & permissions system to update immediately. Security fixes have been backported to all major versions of Winter (1.0, 1.1, and 1.2).
Patches Multiple fixes and defence in depth has been applied to prevent current and future privilege escalation attacks at the lowest level possible.
This security issue has been fixed as of https://wintercms.com/releases/v1.0.477, https://wintercms.com/releases/v1.1.12, https://wintercms.com/releases/v1.2.12.
Weakness type: CWE-284, CWE-639, CWE-915.
Product: winter/wn-backend-module (Composer (PHP)) · Assigned by: GitHub_M · Published: 2026-03-11
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| Composer (PHP) | winter/wn-backend-module | >= 1.2.0, < 1.2.12 | 1.2.12 |
| Composer (PHP) | winter/wn-backend-module | >= 1.1.0, < 1.1.12 | 1.1.12 |
| Composer (PHP) | winter/wn-backend-module | < 1.0.477 | 1.0.477 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| wintercms | winter | >= 1.2.0, < 1.2.12, >= 1.1.0, < 1.1.12, < 1.0.477 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_M | 3.1 | 10 Critical | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H |
| GitHub | 3.1 | 9.9 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: low (any account)
- User interaction: none
- Scope: changed (can affect other components)
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none, automatable no, technical impact total.
- FIRST EPSS (model of 2026-10-21): 0.86% probability of exploitation activity in the next 30 days; percentile 58.
Timeline
- — CVE record published by GitHub_M
- — CVE record last updated
- — GitHub-reviewed advisory GHSA-pgpf-m8m4-6cg6 published (critical)
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-pgpf-m8m4-6cg6 github.com
- CVE.org record CVE-2026-27591 cve.org
- NVD entry CVE-2026-27591 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- wintercms.com wintercms.com
- wintercms.com wintercms.com
- wintercms.com wintercms.com
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