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Concrete CMS EUVDEUVD-2026-76245

| CVE-2026-81913 MEDIUM
URL Redirection to Untrusted Site (Open Redirect) (CWE-601)
2026-09-11 ConcreteCMS GHSA-jwgj-v3j4-f3wg
5.3
CVSS 4.0 · Vendor: ConcreteCMS
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Severity by source

Vendor (ConcreteCMS) PRIMARY
5.3 MEDIUM
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/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
vuln.today AI
4.3 MEDIUM

Network-reachable, no privileges required, but user must click crafted link and authenticate; redirect itself has low integrity impact only.

3.1 AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (ConcreteCMS).

CVSS VectorVendor: ConcreteCMS

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
P
Scope
X

Lifecycle Timeline

1
Analysis Generated
Sep 11, 2026 - 20:02 vuln.today

DescriptionCVE.org

Concrete CMS versions 9.5.0 through 9.5.2 are vulnerable to Open Redirect via the rcURL parameter. An attacker can craft a single link on the site's own domain that sends a user to an arbitrary external site immediately after authentication, facilitating phishing and credential theft. The same handling is present in the registration flow, giving a second entry point on sites with registration enabled. Concrete CMS versions prior to 9.5.0 do not include the rcURL parameter or this allowlist and are not affected. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 5.3 with vector CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Michal M. for reporting.

AnalysisAI

Open redirect in Concrete CMS 9.5.0-9.5.2 allows an unauthenticated attacker to craft a legitimate-looking URL on the victim site that silently forwards an authenticated user to an arbitrary external domain immediately after login or registration. The vulnerability targets the newly introduced rcURL parameter in the authentication and registration flows, making it uniquely scoped to the 9.5.x minor release line. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Recon
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Vulnerability AssessmentAI

Exploitation Exploitation requires that the target site is running Concrete CMS version 9.5.0, 9.5.1, or 9.5.2 - versions outside this range are not vulnerable. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The vendor-assigned CVSS 4.0 score of 5.3 (AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N) accurately reflects the moderate severity of this class of vulnerability. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario Full exploit scenario with step-by-step reproduction available after sign-in.
Remediation Upgrade to Concrete CMS version 9.5.3, which resolves the allowlist bypass in the `rcURL` parameter handling per the 9.5.3 release notes (https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes). … Detailed patch versions, workarounds, and compensating controls in full report.

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EUVD-2026-76245 vulnerability details – vuln.today

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