CVE-2026-18110
A public proof of concept exists; no exploitation attested.
- Published2026-09-15
- Fixed in9.5.3
- WeaknessCWE-862
Am I affected?
Debian, Ubuntu or Red Hat sometimes backport a fix without changing the upstream version number: such a version reads « to verify », never « affected ».With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.
Description
Concrete CMS 9 (9.0.0 through 9.5.2) does not perform an authorization check on the user selector autocomplete endpoint (/ccm/system/user/autocomplete), which backs the "Preview as User" panel and other user-selector components. The endpoint validates only a CSRF-style access token that is bound to the selector's display options rather than to the caller's identity or permissions, and that token is issued to anonymous visitors because the selector renders without an authorization check. Because an empty query resolves to a match-all filter, an unauthenticated attacker can submit an empty search and paginate the results to enumerate every backend account, disclosing the internal user ID, username, and email address of all administrative users, including the super-administrator (user ID 1). No password hashes or session material are disclosed The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 8.7 with vector CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N. Thanks thirtythree and YesWeHack for reporting.
Timeline
dates in UTC- 2026-09-1517:17CVE publishedNVD
Observed activity
isMalicious corpus · updated 2026-10-25 15:37 UTCBlock these indicators
- Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-18110?format=txt
- CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-18110?format=csv
- TAXII collection of exploited CVEs
- The EDL and CSV take an API key on the Pro plan.
Versions per branch
NVD| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 9.x | ≥ 9.0.0, < 9.5.3 | 9.5.3 | NVD |
as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.
Fix
- Update Concretecms concrete cms to 9.5.3
Detection
read 2026-10-25 00:28 UTC- Nuclei template
- none so far ProjectDiscovery
- Exploit-DB
- no entry Exploit-DB
Sources
- CISA-ADPSSVC decisionnone2026-09-22
- OpenCVESSVC decisionnone—
- CNACVSS 4.08.7read 2026-10-23
- NVDCVSS 3.17.5read 2026-10-23
- CNAweakness (CWE)CWE-862read 2026-10-23
- FIRST EPSSEPSS score1.6 %2026-10-25
- PoC-in-GitHubproof of concept1read 2026-10-25
Technical details
- CVSS v3 Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- CVSS 4.0 vector
- CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- Published
- 2026-09-15
- Last Modified
- 2026-09-22
- NVD status
- Analyzed
Frequently asked questions
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