Concrete CMS 9.5.0 and below is vulnerable to IDOR in surveys when sites are running concurrent public surveys and private surveys

published 2026-05-21 5 mo ago modified 2026-09-10 1 mo ago also GHSA-8c7c-h7px-267g , EUVD-2026-31359

cvss: 5.3; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 9%
public exploits: 0; none known

Concrete CMS 9.5.0 and below is vulnerable to IDOR in surveys. To be vulnerable, a site would have to be configured in such a way that both public and private surveys are present on the site. An unauthenticated attacker can vote in the restricted survey by submitting the restricted optionID through the public survey’s endpoint. The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 6.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Zer0daySec https://github.com/Zee99y for reporting

Patch / fix

fixed in 2

packagist concrete5/concrete5 9.5.1
concretecms concrete_cms 9.5.1

CISA SSVC

Exploitation: none
Automatable: yes
Technical impact: partial
Assessed: 5 mo ago (2026-05-22)

Exploit prediction

0.19% chance of exploitation in the next 30 days, higher than 9% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	4.0	6.3	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
CNA	4.0	6.3	CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/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
NVD	3.1	5.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
packagist	concrete5/concrete5	<9.5.1	9.5.1

Affected products

Concrete CMS Concrete CMS

Classification

Weakness

CWE-639 Authorization Bypass Through User-Controlled Key
CWE-565 Reliance on Cookies without Validation and Integrity Checking

References

documentation.concretecms.org /9-x/developers/introduction/version-history/951-release-notes
release-notes, web
nvd.nist.gov /vuln/detail/CVE-2026-8337
advisory
github.com /concretecms/concretecms
package

Sources

CVE List CVE-2026-8337
GitHub Advisory GHSA-8c7c-h7px-267g
NVD CVE-2026-8337

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Summary