# CVE-2026-21861: baserCMS: OS Command Injection Leading to Remote Code Execution (RCE)

> An authenticated administrator can execute arbitrary OS commands on the server via the core update functionality in baserCMS.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 31 Mar 2026
- **Updated:** 31 Mar 2026
- **Also known as:** GHSA-qxmc-6f24-g86g

## What is CVE-2026-21861?

CVE-2026-21861 is a critical command injection vulnerability in Basercms Basercms, published on 31 Mar 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

baserCMS is a website development framework. Prior to version 5.2.3, baserCMS contains an OS command injection vulnerability in the core update functionality. An authenticated administrator can execute arbitrary OS commands on the server due to improper handling of user-controlled input that is directly passed to exec() without sufficient validation or escaping. This issue has been patched in version 5.2.3.

Weakness: CWE-78 (Improper Neutralization of Special Elements used in an OS Command)

## Which versions are affected by CVE-2026-21861?

2 open source packages ship an affected version, including baserproject/basercms. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `baserproject/basercms` | Packagist | All versions | 5.2.3 |
| `baserproject/basercms` | Packagist | All versions | 5.2.3 |

Products: Basercms Basercms.

## How do I fix CVE-2026-21861?

Upgrade baserproject/basercms to 5.2.3 or later.

## Is CVE-2026-21861 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21861 exists.

## Other vulnerabilities in Basercms Basercms

- [CVE-2023-25654](https://insights.sbomify.com/CVE-2023-25654/): baserCMS File Uploader Remote Code Execution (RCE) vulnerability (critical 9.8)
- [CVE-2023-25655](https://insights.sbomify.com/CVE-2023-25655/): baserCMS allows any file to be uploaded (critical 9.8)
- [CVE-2017-10842](https://insights.sbomify.com/CVE-2017-10842/): baserCMS SQL Injection vulnerability (critical 9.8)
- [CVE-2026-30880](https://insights.sbomify.com/CVE-2026-30880/): baserCMS: OS command injection vulnerability in installer (critical 9.2)
- [CVE-2026-30877](https://insights.sbomify.com/CVE-2026-30877/): baserCMS: OS Command Injection in the baserCMS Update Functionality (critical 9.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-21861 and fix it if it is affected.

What it is: CVE-2026-21861 is a critical command injection vulnerability in Basercms Basercms, published on 31 Mar 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21861 exists.

Affected packages and fixed versions:
- baserproject/basercms (Packagist): affected all versions; fixed in 5.2.3
- baserproject/basercms (Packagist): affected all versions; fixed in 5.2.3

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-2026-21861/ (Markdown: https://insights.sbomify.com/CVE-2026-21861/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-21861
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-21861
- OSV: https://osv.dev/vulnerability/CVE-2026-21861

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-21861/
Summaries are generated and may contain mistakes; the official description above is the record.