CVE-2026-81913Network attack vectorHinoki check available

Open redirect via unchecked post-authentication rcURL

Published Sep 11, 2026 · Updated Sep 11, 2026

Open redirect in Concrete CMS 9.5.0 through 9.5.2 allows remote attackers to send users to external sites after authentication. The login and registration forwarding logic accepts the rcURL query parameter as an external destination without enforcing the intended allowlist. Exploitation requires a user to follow a crafted same-domain link and authenticate; registration is a second entry point only when enabled.

CVSS severity5.3
Medium
EPSS probability0.52%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Open redirect in Concrete CMS 9.5.0 through 9.5.2 allows remote attackers to send users to external sites after authentication. The login and registration forwarding logic accepts the rcURL query parameter as an external destination without enforcing the intended allowlist. Exploitation requires a user to follow a crafted same-domain link and authenticate; registration is a second entry point only when enabled.

The record

CVE
CVE-2026-81913
Published
Sep 11, 2026
Updated
Sep 11, 2026
Vendor
Concrete CMS
Product
Concrete CMS
Classifications
T1566.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 11, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=9.5.0 <=9.5.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Concrete CMS · Concrete CMSversion=9.5.0 <=9.5.2

Published CVSS scores

5.3Concrete CMS security teamCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1566.002Spearphishing Link

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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