typo3/cms-core security advisory

CVE-2026-19418: TYPO3-CORE-SA-2026-021: Broken Access Control in Backend and Install Tool

CVE-2026-19418 is a high-severity missing authorization vulnerability in the PHP package typo3/cms-core (CVSS 7.3), published 11 August 2026. It is fixed in 13.4.34 and 14.3.6, one per release line; earlier versions on each line are affected. Exploiting it needs a low-privilege user account.

high 7.3 published 2026-08-11 · updated 2026-10-23

Affected versions: >= 13.0.0, < 13.4.34
>= 14.0.0, < 14.3.6
Fixed in: 13.4.34, 14.3.6
Newest release: 14.3.10
Severity: High · CVSS 7.3
Type: Missing authorization check
CWE-346, CWE-352
Exploited in the wild: Not on the CISA KEV list
checked 2026-11-04

Is your typo3/cms-core version affected?

Run composer show typo3/cms-core in your project, then enter the version. We check it against this and every other known typo3/cms-core advisory.

Who can exploit CVE-2026-19418

Access: A normal, low-privilege user account in the app.
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: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Your app is only exposed if it uses the affected part of typo3/cms-core. 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-2026-19418 in typo3/cms-core

Find the installed version: composer show typo3/cms-core. If you never required it yourself, composer why typo3/cms-core shows which package pulls it in.
Update it: composer update typo3/cms-core --with-all-dependencies. You need the fixed version for your release line (13.4.34 and 14.3.6).
If Composer will not go that high, your composer.json constraint is holding it back. Widen it (for example "typo3/cms-core": "^14.3.6" if you can take that version), or upgrade the package that requires it.
Run composer audit. It reads the same advisory data and should no longer list CVE-2026-19418.
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 missing authorization issues while the upgrade waits. None of it replaces the fix.

Remove accounts you do not need and review what each role can do.
Put the admin area behind a VPN, IP allow-list or extra login until you upgrade.
If your app does not use the affected feature, note that in your audit, but still plan the upgrade.

The CVE-2026-19418 advisory

The referrer enforcement introduced with TYPO3-CORE-SA-2020-006 (CVE-2020-11069) became ineffective in TYPO3 v13.0, where TYPO3 CMS started serving the backend and Install Tool applications from the site's main entry script instead of the dedicated typo3/ directory. Whether a request originated from the backend or Install Tool itself was determined by comparing the referrer against the directory of the entry script, which since then is the site root. As a consequence, requests originating from any script running on one of the TYPO3 instance's own domains, such as a frontend page, were accepted by backend routes and Install Tool endpoints. Attackers able to execute JavaScript on one of those domains, for instance by exploiting a cross-site scripting vulnerability, could invoke these endpoints via Fetch/XHR with the privileges of an authenticated victim's user session. This issue affects TYPO3 CMS versions 13.0.0-13.4.33 and 14.0.0-14.3.5.

Description from the CVE record, via the NVD entry for CVE-2026-19418. Advisory title: “TYPO3-CORE-SA-2026-021: Broken Access Control in Backend and Install Tool”.

References

Other typo3/cms-core advisories

high CVE-2026-11607: TYPO3-CORE-SA-2026-019: Broken Access Control in Form Framework 2026-06-09
medium CVE-2026-49740: TYPO3-CORE-SA-2026-018: Insecure Deserialization in Core API 2026-06-09
high CVE-2026-49741: TYPO3-CORE-SA-2026-017: Privilege Escalation & SQL Injection in Form Framework 2026-06-09
low CVE-2026-49738: TYPO3-CORE-SA-2026-016: Broken Access Control in File Abstraction Layer 2026-06-09
medium CVE-2026-47352: TYPO3-CORE-SA-2026-015: Broken Access Control in Backend API 2026-06-09
medium CVE-2026-47351: TYPO3-CORE-SA-2026-014: Broken Access Control in Clipboard 2026-06-09

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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.