CVE-2026-81900Concrete CMS before 9.5.3 is vulnerable to Stored XSS in the YouTube block (vWidth/vHeight)
Updated under an hour ago ()
Does this affect you?
It affects Concrete CMS and 1 other product. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
Do this next
Free account, 1 product
Concrete CMS before 9.5.3 applied only trim() to the YouTube block's stored width and height values and printed them into iframe HTML attributes without escaping or integer casting, resulting in stored cross-site scripting. A user with edit_block permission could inject an event handler that executed script for visitors rendering the page, acting with administrative privileges where the victim was an administrator. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 7.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks sh4d0byss for reporting.
- CVSS
- 7.3 HIGH (v4.0, CNA)CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- Weakness (CWE)
- CWE-79
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- ConcreteCMS
- NVD analysis
- Analyzed
- Record last updated
- Sep 15, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Concrete CMS Concrete CMS concrete_cms:concrete_cms (from the name) | from 5.0.0 through 9.5.2 | CNA record |
concretecms concrete_cms concretecms:concrete_cms | before 9.5.3 | NVD |
References
- https://documentation.concretecms.org/developers/introduction/version-history/953-release-notesrelease-notes, broken-link
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.