# CVE-2026-18424: Server-side request forgery in Concrete CMS

> Low-privileged users can bypass SSRF protections in Concrete CMS to fetch internal resources via DNS rebinding during file imports.

- **Severity:** Low 2.1 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Sep 2026
- **Updated:** 20 Sep 2026
- **Also known as:** GHSA-fmfq-8qcq-wrx4

## What is CVE-2026-18424?

CVE-2026-18424 is a low-severity server-side request forgery vulnerability in Concretecms Concrete Cms, published on 15 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official 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.

Weakness: CWE-918 (Server-Side Request Forgery)

## Which versions are affected by CVE-2026-18424?

It affects 1 product.


Products: Concretecms Concrete Cms.

## How do I fix CVE-2026-18424?

No fix has been published for CVE-2026-18424 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-18424 being exploited?

There is no known exploitation of CVE-2026-18424 in the wild and no public exploit code.

## Other vulnerabilities in Concretecms Concrete Cms

- [CVE-2023-48648](https://insights.sbomify.com/CVE-2023-48648/): Concrete CMS allows unauthorized access because directories can be created with insecure permissions (critical 9.8)
- [CVE-2022-21829](https://insights.sbomify.com/CVE-2022-21829/): Code injection in concrete CMS (critical 9.8)
- [CVE-2021-22958](https://insights.sbomify.com/CVE-2021-22958/): Server-Side Request Forgery vulnerability in concrete5 (critical 9.8)
- [CVE-2021-40098](https://insights.sbomify.com/CVE-2021-40098/): Path traversal in n/a (critical 9.8)
- [CVE-2026-8134](https://insights.sbomify.com/CVE-2026-8134/): Concrete CMS Vulnerable to Relative Path Traversal (critical 9.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-18424 and fix it if it is affected.

What it is: CVE-2026-18424 is a low-severity server-side request forgery vulnerability in Concretecms Concrete Cms, published on 15 Sep 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-18424 in the wild and no public exploit code.

Affected product: Concretecms Concrete Cms. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-18424/ (Markdown: https://insights.sbomify.com/CVE-2026-18424/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-18424
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-18424
- OSV: https://osv.dev/vulnerability/CVE-2026-18424

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-18424/
Summaries are generated and may contain mistakes; the official description above is the record.