Machine-written summary
Summary written by Claude Haiku from the source advisory. Not reviewed by a person.
Concrete CMS versions 9.5.0 and below (Packagist concrete5/concrete5, affected before 9.5.1) contain an insecure deserialization flaw in the ExpressEntryList block controller. An attacker who already holds an administrator account with permission to add blocks to an area can use the REST API to bypass the existing protection and store a malicious serialized payload, which runs when an administrator views or edits that block, potentially giving full control of the server. Upgrade to version 9.5.1 or later.
Not analysed yet
We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.
Severity and exploitation
| Score | Rating | CVSS | Vector | Source |
|---|---|---|---|---|
| 8.9 | High | 4.0 | CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H | CNA (ConcreteCMS) |
- CISA KEV Not listed.
- EPSS 0.0047, the 41st percentile, on 11 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.
Timeline
- 31 Oct 2026, 14:01 UTC First seen by agentprime
- 31 Oct 2026, 14:01 UTC Confirmed by OSV