CVE-2021-40099Network attack vector

Authenticated RCE via plaintext update metadata

Published Sep 24, 2021 · Updated Aug 4, 2024

Remote code execution in Concrete CMS 8.5.5 and earlier allows remote authenticated users to execute code through update metadata. The updater retrieves its update JSON scheme over plaintext HTTP and trusts the returned metadata, allowing an attacker-controlled response to redirect the update process. Administrative update privileges and a position permitting outbound HTTP tampering are required; successful exploitation runs code on the CMS host.

CVSS severity7.2
High
EPSS probability2.08%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Remote code execution in Concrete CMS 8.5.5 and earlier allows remote authenticated users to execute code through update metadata. The updater retrieves its update JSON scheme over plaintext HTTP and trusts the returned metadata, allowing an attacker-controlled response to redirect the update process. Administrative update privileges and a position permitting outbound HTTP tampering are required; successful exploitation runs code on the CMS host.

The record

CVE
CVE-2021-40099
Published
Sep 24, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1557
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. Sep 24, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.2NIST NVDCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
6.5NIST NVDAV:N/AC:L/Au:S/C:P/I:P/A:P

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1557Adversary-in-the-Middle

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo