CVE-2026-34559: CI4MS: Blogs Tags Full Account Takeover for All-Roles & Privilege-Escalation via Stored DOM XSS

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.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.4%, percentile 32: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 32% of all scored CVEs (low). 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 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 when creating or editing blog tags. An attacker can inject a malicious JavaScript payload into the tag name field, which is then stored server-side. This stored payload is later rendered unsafely across public tag pages and administrative interfaces without proper output encoding, leading to stored cross-site scripting (XSS). This issue has been patched in version 0.31.0.0.

From the GitHub advisory

Summary Vulnerability: Stored DOM XSS via Blog Tag Name (Persistent Payload Injection) - Stored Cross-Site Scripting via Unsanitized Blog Tag Name in Blog Management

Description The application fails to properly sanitize user-controlled input when creating or editing blog tags. An attacker can inject a malicious JavaScript payload into the tag name field, which is then stored server-side.

This stored payload is later rendered unsafely across public tag pages and administrative interfaces without proper output encoding, leading to stored cross-site scripting (XSS).

Affected Functionality - Blog tag creation functionality - Blog tag editing functionality - Blog tag storage and retrieval logic

Attack Scenario - An attacker creates or edits a blog tag name to include a malicious XSS payload. - The application stores this value without sanitization or encoding. - The payload persists and executes whenever the tag name is rendered in affected views.

Weakness type: CWE-79.

Product: ci4-cms-erp/ci4ms (Composer (PHP)) · Assigned by: GitHub_M · Published: 2026-04-01

Affected and fixed versions

Severity scores

• 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 poc, automatable no, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.39% probability of exploitation activity in the next 30 days; percentile 32.

Timeline

• 2026-04-01 — CVE record published by GitHub_M
• 2026-04-01 — GitHub-reviewed advisory GHSA-4333-387x-w245 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-4333-387x-w245 github.com
2. CVE.org record CVE-2026-34559 cve.org
3. NVD entry CVE-2026-34559 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

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