october/system security advisory

CVE-2026-26067: October CMS has Safe Mode Bypass via CSS Preprocessor Compilers

CVE-2026-26067 is a medium-severity information disclosure vulnerability in the PHP package october/system (CVSS 4.9), published 21 April 2026. No fixed release exists yet: the newest version, 1.1.12, is affected. Exploiting it needs an admin-level account.

medium 4.9 affects newest 1.1.12 published 2026-04-21 · updated 2026-10-26

Affected versions: < 3.7.14
>= 4.0.0, < 4.1.10
Fixed in: no fix yet
Newest release: 1.1.12
Severity: Medium · CVSS 4.9
Type: Information disclosure
CWE-184, CWE-863
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-2026-26067

Access: A high-privilege account in the app, such as an admin.

CVSS vector (scored by GitHub): CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/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-2026-26067 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-2026-26067.
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 information disclosure issues while the upgrade waits. None of it replaces the fix.

Make sure APP_DEBUG (or your framework's debug mode) is off in production and error pages show no stack traces.
If your app does not use the affected feature, note that in your audit, but still plan the upgrade.

The CVE-2026-26067 advisory

October is a Content Management System (CMS) and web platform. Prior to 3.7.14 and 4.1.10, a server-side information disclosure vulnerability was identified in the handling of CSS preprocessor files. Backend users with Editor permissions could craft .less, .sass, or .scss files that leverage the compiler's import functionality to read arbitrary files from the server. This worked even with cms.safe_mode enabled. This vulnerability is fixed in 3.7.14 and 4.1.10.

Description from the CVE record, published by GitHub (the CVE Numbering Authority), via the NVD entry for CVE-2026-26067. Advisory title: “October CMS has Safe Mode Bypass via CSS Preprocessor Compilers”.

References

GitHub advisory GHSA-3888-q23f-x7qh 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
low CVE-2026-27937: October CMS: Reflected XSS via DataTable Form Widget 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.