CVE-2026-18424

Analyzed Analyzed - Analysis Complete

Server-Side Request Forgery in Concrete CMS via DNS Pinning Bypass

Publication date: 2026-09-15

Last updated on: 2026-09-21

Assigner: ConcreteCMS

Description

Concrete CMS 9.0.0 to 9.5.2 is vulnerable to Server-Side Request Forgery iremote file import via cross-port reuse of a host's validated DNS pin. When multiple remote URLs share the same host, only the first `ValidatedRemoteUrl` is retained and reused for every later URL with that host. A low-privileged authenticated user permitted to import files could therefore supply a DNS-rebinding host that resolved to a public address during validation and to a private or loopback address during the unpinned download, causing the server to fetch internal-only resources such as loopback services, internal admin panels, or cloud metadata endpoints and to save the responses into the file manager. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 2.1 with vector CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N. Thanks Ahmad Wicaksono (sonix03) for reporting.

CVSS Scores

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Meta Information

Published

2026-09-15

Last Modified

2026-09-21

Generated

2026-10-06

AI Q&A

2026-09-16

EPSS Evaluated

2026-10-04

NVD

CVE-2026-18424

EUVD

EUVD-2026-79503

Affected Vendors & Products

Vendor	Product	Version / Range
concretecms	concrete_cms	From 9.0.0 (inc) to 9.5.3 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-918	The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.

Attack-Flow Graph

Executive Summary

Concrete CMS versions 9.0.0 to 9.5.2 are vulnerable to Server-Side Request Forgery (SSRF) through cross-port reuse of a host's validated DNS pin. When multiple remote URLs share the same host, only the first validated URL is reused for all subsequent URLs with that host. This allows a low-privileged authenticated user to import files via a DNS-rebinding attack, where a host resolves to a public address during validation but to a private or loopback address during download, causing the server to fetch internal resources.

Detection Guidance

Detecting this SSRF vulnerability in Concrete CMS requires checking for outdated versions (9.0.0 to 9.5.2) and monitoring file import functionality. Inspect server logs for unusual outbound requests to private or loopback addresses during file imports. Check if multiple remote URLs with the same host are processed sequentially, as this may indicate the DNS pinning bypass.

Impact Analysis

An attacker with low privileges could exploit this to make the server access internal services like loopback services, admin panels, or cloud metadata endpoints. The server would then save these responses into the file manager, potentially exposing sensitive internal data or enabling further attacks.

Compliance Impact

This vulnerability could lead to unauthorized access to internal systems, potentially exposing personal or sensitive data. This may violate compliance requirements under GDPR (data protection) or HIPAA (health information privacy), depending on the data accessed and the organization's policies.

Mitigation Strategies

Upgrade Concrete CMS to a version beyond 9.5.2 to address the SSRF vulnerability via DNS pinning bypass. Review file import permissions to ensure only trusted users can perform remote imports. Monitor network traffic for unusual internal requests originating from the CMS server.

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