october/system security advisory

CVE-2026-27937: October CMS: Reflected XSS via DataTable Form Widget

CVE-2026-27937 is a low-severity reflected XSS vulnerability in the PHP package october/system (CVSS 3.1), published 21 April 2026. No fixed release exists yet: the newest version, 1.1.12, is affected. It can be exploited without an account.

low 3.1 affects newest 1.1.12 published 2026-04-21 · updated 2026-10-26

Affected versions: < 3.7.16
>= 4.0.0, < 4.1.16
Fixed in: no fix yet
Newest release: 1.1.12
Severity: Low · CVSS 3.1
Type: Reflected cross-site scripting (XSS)
CWE-79
Exploited in the wild: Not on the CISA KEV list
checked 2026-11-04

Is your october/system version affected?

Run composer show october/system in your project, then enter the version. We check it against this and every other known october/system advisory.

Who can exploit CVE-2026-27937

Access: No account. Anyone who can send a request to an app that uses the affected code.
Interaction: A user also has to do something, such as open a link or a page the attacker prepared.
Conditions: It only works under specific conditions the attacker does not fully control (CVSS rates the attack as high complexity).

CVSS vector (scored by GitHub): CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N

Your app is only exposed if it uses the affected part of october/system. The advisory below says which part that is. If you are not sure, upgrade anyway: it costs less than finding out.

How to fix CVE-2026-27937 in october/system

Find the installed version: composer show october/system. If you never required it yourself, composer why october/system shows which package pulls it in.
There is no fixed release yet. Read the advisory below for a workaround, and avoid or switch off the affected feature until a fix ships.
Check back on the october/system page. It updates daily from Packagist.
Run composer audit. It reads the same advisory data and should no longer list CVE-2026-27937.
Commit composer.lock and deploy it. On the server, run composer install --no-dev from the lock file, not composer update.

If you cannot upgrade yet

General hardening for reflected XSS issues while the upgrade waits. None of it replaces the fix.

Escape output in your own templates and add a Content-Security-Policy that blocks inline scripts.
Limit who can save the content the advisory names (for example rich text, SVG or form fields).
If your app does not use the affected feature, note that in your audit, but still plan the upgrade.

The CVE-2026-27937 advisory

October is a Content Management System (CMS) and web platform. Prior to 3.7.16 and 4.1.16, a reflected Cross-Site Scripting (XSS) vulnerability was identified in the backend DataTable widget where a query parameter was rendered without proper output escaping. This vulnerability is fixed in 3.7.16 and 4.1.16.

Description from the CVE record, published by GitHub (the CVE Numbering Authority), via the NVD entry for CVE-2026-27937. Advisory title: “October CMS: Reflected XSS via DataTable Form Widget”.

References

GitHub advisory GHSA-jj38-h5w5-mvpf github.com

Other october/system advisories

low CVE-2026-49400: October CMS: PHP Object Injection via Backend Widget Session Storage 2026-09-14
low CVE-2026-46696: October CMS: Safe Mode Sandbox Bypass via Session Store and Forwarded Builder Calls 2026-09-14
low CVE-2026-29179: October CMS: Editor Sub-Permission Bypass for Asset and Blueprint File Operations 2026-04-21
medium CVE-2026-26067: October CMS has Safe Mode Bypass via CSS Preprocessor Compilers 2026-04-21
medium CVE-2026-24907: October CMS has Stored XSS in Event Log Mail Preview 2026-04-14
medium CVE-2026-24906: October CMS has Stored XSS in Backend Editor Markup Classes 2026-04-14

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Where this data comes from

Affected and fixed versions: the Packagist security advisories API (GitHub Advisory Database and FriendsOfPHP), the same data composer audit uses. Synced 2026-11-03.
Description, score, weakness and references: NIST National Vulnerability Database (NVD), checked 2026-11-04. This product uses data from the NVD API but is not endorsed or certified by the NVD.
Exploited-in-the-wild status: the CISA Known Exploited Vulnerabilities catalog, checked 2026-11-04.
Compiled by Daniel Lasek at Laskyr from the sources above. The summary, “who can exploit it”, “how to fix it” and hardening sections are our plain-English reading of the record and are generated from it. The quoted description is the record's own text. Spot an error? Tell us.