CVE-2026-27599: ci4-cms-erp/ci4ms: System Settings (Mail Settings) Full Platform Compromise & Full Account Takeover for All-Roles & Privilege-Escalation via Stored DOM XSS

Should you act?

Normal patch cycle

No exploitation signal; fix it in your next routine update if you are affected. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.4%, percentile 36: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 36% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Needs an account (high (admin)). Exposure depends on who can log in.
• Only applies if your dependency tree includes ci4-cms-erp/ci4ms (Composer (PHP)) <= 0.28.6.0, fixed in 0.31.0.0. Check your lockfile, including transitive dependencies.

What it is

CI4MS is a CodeIgniter 4-based CMS skeleton that delivers a production-ready, modular architecture with RBAC authorization and theme support. Prior to version 0.31.0.0, the application fails to properly sanitize user-controlled input within System Settings – Mail Settings. Several configuration fields, including Mail Server, Mail Port, Email Address, Email Password, Mail Protocol, and TLS settings, accept attacker-controlled input that is stored server-side and later rendered without proper output encoding. This issue has been patched in version 0.31.0.0.

From the GitHub advisory

Summary Vulnerability: Stored DOM XSS via System Settings – Mail Settings (Same-Page Attribute Breakout & Persistent Payload Injection) - Stored Cross-Site Scripting via Unsanitized Mail Settings Configuration Fields

Description The application fails to properly sanitize user-controlled input within System Settings – Mail Settings. Several configuration fields, including Mail Server, Mail Port, Email Address, Email Password, Mail Protocol, and TLS settings, accept attacker-controlled input that is stored server-side and later rendered without proper output encoding.

Unlike public-facing XSS that executes on landing pages, this vulnerability executes immediately on the same settings page. The injected payload breaks out of the HTML attribute context and is interpreted by the browser when rendered, resulting in same-page DOM-based XSS.

This represents different functionality and a separate vulnerability from landing-page injection.

Example Affected Fields - Mail Server: test - Mail Port: 465 - Email Address: simple@gmail.com - Email Password: (any input) - Mail Protocol: SMTP - Domain: simple@domain.com

Weakness type: CWE-79.

Product: ci4-cms-erp/ci4ms (Composer (PHP)) · Assigned by: GitHub_M · Published: 2026-03-30

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: high (admin)
• User interaction: none
• Scope: unchanged

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 poc, automatable no, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.42% probability of exploitation activity in the next 30 days; percentile 36.

Timeline

• 2026-03-30 — CVE record published by GitHub_M
• 2026-03-30 — GitHub-reviewed advisory GHSA-66m2-v9v9-95c3 published (critical)
• 2026-04-02 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-66m2-v9v9-95c3 github.com
2. CVE.org record CVE-2026-27599 cve.org
3. NVD entry CVE-2026-27599 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. mega.nz mega.nz

Critical Composer (PHP) advisories · Today’s Security Digest