# CVE-2026-8426: Concrete CMS does not validate a CSRF token before processing requests to `/dashboard/extend/update/prepare_remote_upgrade/` > An attacker can exploit a CSRF vulnerability in Concrete CMS to overwrite packages and execute arbitrary code if the victim has marketplace connectivity and package installation enabled. - **Severity:** High 7.5 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** A user has to click or open something - **Fix available:** Yes - **Published:** 21 May 2026 - **Updated:** 22 May 2026 - **Also known as:** GHSA-5rj5-gfmr-hrc3 ## What is CVE-2026-8426? CVE-2026-8426 is a high-severity vulnerability in Concretecms Concrete Cms, published on 21 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link. ### Official description Concrete CMS 9.5.0 and below does not validate a CSRF token before processing requests to /dashboard/extend/update/prepare_remote_upgrade/. An attacker who controls the remote package returned for a known marketplace item ID can overwrite the package PHP on disk and force its upgrade() method to execute in a single browser navigation. This results in remote code execution as the web server user.   In order to be vulnerable, the victim must be passing canInstallPackages, victim site must be connected to the Concrete marketplace; and the attacker controls the package returned for a marketplace item ID already installed on the victim site. The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 7.5 with vector CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks https://github.com/maru1009 for reporting. Weakness: CWE-829 (Inclusion of Functionality from Untrusted Control Sphere), CWE-352 (Cross-Site Request Forgery) ## Which versions are affected by CVE-2026-8426? 2 open source packages ship an affected version, including concrete5/concrete5. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `concrete5/concrete5` | Packagist | All versions | 9.5.1 | | `concrete5/concrete5` | Packagist | All versions | 9.5.1 | Products: Concretecms Concrete Cms. ## How do I fix CVE-2026-8426? Upgrade concrete5/concrete5 to 9.5.1 or later. ## Is CVE-2026-8426 being exploited? There is no known exploitation of CVE-2026-8426 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-2026-8426 and fix it if it is affected. What it is: CVE-2026-8426 is a high-severity vulnerability in Concretecms Concrete Cms, published on 21 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link. Exploitation: There is no known exploitation of CVE-2026-8426 in the wild and no public exploit code. Affected packages and fixed versions: - concrete5/concrete5 (Packagist): affected all versions; fixed in 9.5.1 - concrete5/concrete5 (Packagist): affected all versions; fixed in 9.5.1 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-2026-8426/ (Markdown: https://insights.sbomify.com/CVE-2026-8426/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-8426 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-8426 - OSV: https://osv.dev/vulnerability/CVE-2026-8426 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-8426/ Summaries are generated and may contain mistakes; the official description above is the record.