baserCMS Path Traversal Leads to Arbitrary File Write and RCE via Theme File API

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.2 · CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

EPSS

• CVE-2026-30940: 1.07% estimated exploitation activity in the next 30 days; percentile 64.83 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A path traversal vulnerability exists in the baserCMS 5.x theme file management API (/baser/api/admin/bc-theme-file/themefiles/add.json) that allows arbitrary file write. An authenticated administrator can include ../ sequences in the path parameter to create a PHP file in an arbitrary directory outside the theme directory, which may result in remote code execution (RCE). Affected Code File: plugins/bc-theme-file/src/Service/BcThemeFileService.php Attack Scenario 1. The attacker compromises an administrator account (password leak, brute force, etc.) 2. Obtains an access token via API login 3. Specifies path: "../../../../webroot/" in the theme file creation API 4. A PHP file is created in the webroot 5. The attacker accesses the created PHP file to achieve RCE Reproduction Steps Vulnerability Details | Item | Details | |------|---------| | CWE | CWE-22: Path Traversal, CWE-73: External Control of File Name or Path | | Impact | Arbitrary file write, Remote Code Execution (RCE)…

Published by the source

31 Mar 2026, 22:47 UTC

Last modified by the source

31 Mar 2026, 22:47 UTC

Source last checked

26 Oct 2026, 14:39 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-c5c6-37vq-pjcq

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-30940

Advisory: baserCMS Path Traversal Leads to Arbitrary File Write and RCE via Theme File API
IDs: CVE-2026-30940, GHSA-c5c6-37vq-pjcq
Record: https://patchnext.com/advisories/cve-2026-30940 (revision 1, source checked 26 Oct 2026, 14:39 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: baserproject/basercms 5.2.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist baserproject/basercms: affected <= 5.2.2; fixed in 5.2.3

## Suggested inspection (read-only)
- Packagist baserproject/basercms: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on baserproject/basercms.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-c5c6-37vq-pjcq (GitHub-reviewed advisory GHSA-c5c6-37vq-pjcq lists affected ranges: Packagist baserproject/basercms >=0 <=5.2.2)

Commands are suggestions: review each one before running it.