CVE-2026-81900
Low
No strong exploitation signal.
CVSS base
6.1
MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
EPSS — probability of exploitation (30 days)
0.1%
4.1th percentile
CISA KEV
Not listed
Weakness / dates
CWE-79
Published 2026-09-14 · modified 2026-09-16
CVSS breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
| Attack Vector | N | Network |
| Attack Complexity | L | Low |
| Privileges Required | N | None |
| User Interaction | R | Required |
| Scope | C | Changed |
| Confidentiality | L | Low |
| Integrity | L | Low |
| Availability | N | None |
Timeline
- 2026-09-14 — Published (NVD)
- 2026-09-16 — Last modified (NVD)
Description
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.