EUVD-2026-55971
GHSA-4f2f-jr2m-j7p4
Severity by source
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
AC:H because exploitation requires a separate XSS vulnerability as a prerequisite; PR:N because the attacker needs no TYPO3 credentials; S:C because frontend-scope JavaScript crosses into the backend administrative scope.
Primary rating from Vendor (TYPO3).
CVSS VectorVendor: TYPO3
Lifecycle Timeline
3DescriptionCVE.org
The referrer enforcement introduced with TYPO3-CORE-SA-2020-006 https://news.typo3.com/security/advisory/typo3-core-sa-2020-006 ( CVE-2020-11069 https://www.cve.org/CVERecord ) 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.
AnalysisAI
Broken referrer enforcement in TYPO3 CMS backend and Install Tool allows an attacker with JavaScript execution capability on any of the site's own domains to invoke privileged backend routes and Install Tool endpoints using an authenticated victim's session. The regression was introduced in TYPO3 13.0.0 when both the backend and Install Tool were moved to serve from the site root entry point rather than the dedicated /typo3/ subdirectory, causing the ReferrerEnforcer to accept any same-origin Referer header as legitimate backend traffic. Affected versions are TYPO3 CMS 13.0.0-13.4.33 and 14.0.0-14.3.5; no public exploit code has been identified at time of analysis.
Technical ContextAI
The root cause is classified as CWE-346 (Origin Validation Error). Prior to TYPO3 13.0.0, the backend and Install Tool were served from the dedicated /typo3/ subdirectory, so the ReferrerEnforcer correctly validated that Referer headers pointed into that directory. Starting in v13.0.0, both applications were unified under the site's main entry script, moving the effective base path to the site root (e.g., https://example.org/). The existing CoreReferrerEnforcer compared the Referer against the request host root, meaning any script on the same domain - including frontend pages - would pass the check. The fix, visible in commit ae0abd329d52285fe6e92804c3608820ad45e872, introduces a backend-specific TYPO3\CMS\Backend\Http\Security\ReferrerEnforcer subclass that resolves the actual backend entry point URI via BackendEntryPointResolver and enforces that Referer headers must start with that URI, not merely the host root. Affected CPE: cpe:2.3:a:typo3:typo3_cms covering versions 13.0.0-13.4.33 and 14.0.0-14.3.5.
RemediationAI
Upgrade TYPO3 CMS to version 13.4.34 (for the 13.x branch) or 14.3.6 (for the 14.x branch), as documented in the vendor advisory at https://typo3.org/security/advisory/typo3-core-sa-2026-021 and confirmed by EUVD-2026-55971. The underlying fix is available in GitHub commits ae0abd329d52285fe6e92804c3608820ad45e872, a0e8ee06a40e959b9e7b06a4b1cb19d3a0d3dcf7, and 4a75e862c589c85d795d7c65dcdc835f8f413efc. For installations that cannot be patched immediately, the most targeted compensating control is auditing and remediating all XSS vulnerabilities in frontend components, since this vulnerability's attack path has XSS as a hard prerequisite; eliminating the XSS vector closes the attack chain without touching the referrer logic. As an architectural mitigation with meaningful trade-offs, hosting the TYPO3 backend on a separate subdomain or domain from the public frontend would break the same-origin requirement entirely, but this requires significant infrastructure changes and may affect SSO or session sharing configurations.
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Same weakness CWE-346 – Origin Validation Error
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External POC / Exploit Code
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