CVE-2026-81900
CVE-2026-81900 is a Cross-site Scripting (XSS) vulnerability. O3 Security confirms whether CVE-2026-81900 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
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,…
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.
Detection & mitigation playbook
VulnerabilityDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for the affected component. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Remediation status
No patched version of the affected component has shipped for CVE-2026-81900 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-81900 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-81900. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-81900 in your dependencies?
O3 detects CVE-2026-81900 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.