CVE-2026-8139 Concrete CMS 9.5.0 and below is vulnerable to Stored XSS via external-link page cvName

What is CVE-2026-8139?

CVE-2026-8139 is a low-severity cross-site scripting vulnerability in Concretecms Concrete Cms, published on 21 May 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.

Official description

Concrete CMS 9.5.0 and below is vulnerable to Stored XSS via external-link page cvName because updateCollectionAliasExternal bypasses being sanitized. The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 2.0 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N.  Thanks Yonatan Drori (Tenzai) for reporting.

Weakness: CWE-79

Which versions are affected by CVE-2026-8139?

2 open source packages ship an affected version, including concrete5/concrete5. It affects 1 product.

Products include Concretecms Concrete Cms.

How do I fix CVE-2026-8139?

Upgrade concrete5/concrete5 to 9.5.1 or later.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2026-8139 being exploited?

There is no known exploitation of CVE-2026-8139 in the wild and no public exploit code.

Other vulnerabilities in Concretecms Concrete Cms

• CVE-2023-48648 Concrete CMS allows unauthorized access because directories can be created with insecure permissions Critical 9.8
• CVE-2022-21829 Code injection in concrete CMS Critical 9.8
• CVE-2021-22958 Server-Side Request Forgery vulnerability in concrete5 Critical 9.8
• CVE-2021-40098 Path traversal in n/a Critical 9.8
• CVE-2026-8134 Concrete CMS Vulnerable to Relative Path Traversal Critical 9.4

All Concretecms Concrete Cms vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-pcrh-gj77-j4mw.