CVE-2026-21861

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.

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.

Summary

In the core update functionality of baserCMS, some parameters sent from the admin panel are passed to the exec() function without proper validation or escaping. This issue allows an authenticated CMS administrator to execute arbitrary OS commands on the server (Remote Code Execution, RCE).

This vulnerability is not a UI-level issue such as screen manipulation or lack of CSRF protection, but rather stems from a design that directly executes input values received on the server side as OS commands. Therefore, even if buttons are hidden in the UI, or even if CakePHP's CSRF/FormProtection (SecurityComponent) ensures that only legitimate POST requests are accepted, an attack is possible as long as a request containing a valid token is processed within an administrator session.

---

Vulnerability Information

| Item | Details | | ---- | ------- | | CWE | CWE-78: Improper Neutralization of Special Elements used in an OS Command | | Impact | Remote Code Execution (RCE) | | Severity | Critical | | Attack Requirements | Administrator privileges required | | Reproducibility | Reproducible (confirmed multiple times) | | Test Environment | baserCMS 5.2.2 (Docker / development environment) |

---

Affected Areas

• Controller
  • PluginsController::get_core_update()
• Service
  • PluginsService::getCoreUpdate()
• Affected Endpoint
  • /baser/admin/baser-core/plugins/get_core_update

---

Technical Details

Vulnerable Code Flow

PluginsController::get_core_update()
  ↓ Retrieves php parameter from POST data
PluginsService::getCoreUpdate($targetVersion, $php, $force)
  ↓ Concatenates $php into command string without validation or escaping
exec($command)

Relevant Code (Excerpt)

PluginsController.php

$service->getCoreUpdate(
    $request->getData('targetVersion') ?? '',
    $request->getData('php') ?? 'php',
    $request->getData('force'),
);

PluginsService.php

$command = $php . ' ' . ROOT . DS . 'bin' . DS . 'cake.php composer ' .
           $targetVersion . ' --php ' . $php . ' --dir ' . TMP . 'update';

exec($command, $out, $code);

The $php parameter is user input, and none of the following countermeasures are in place:

• Restriction via allowlist
• Validation via regular expression
• Escaping via escapeshellarg() or similar

---

Attack Scenario

1. The attacker logs in as a CMS administrator
2. Sends a POST request to the core update functionality in the admin panel
3. Specifies a string containing OS commands in the php parameter
4. exec() is executed on the server side, running the arbitrary OS command

Example Attack Input (Conceptual)

php=php;id>/tmp/rce_test;#

---

Verification Results (PoC)

Execution Result

$ docker exec bc-php cat /tmp/rce_test
uid=1000(www-data) gid=1000(www-data) groups=1000(www-data)

The above confirms that OS commands can be executed with www-data privileges.

Additional Notes

• Reproducible through the legitimate flow in the admin panel (browser)
• Succeeds even with CSRF/FormProtection tokens included in a legitimate request
• Failure cases (400/403) have also been investigated and differentiated
• Confirmed reproducible via resending HTTP requests with tools such as curl (resending the same request containing valid tokens)

---

Impact

If this vulnerability is exploited, the following becomes possible:

• Retrieval of server information
• Reading/writing arbitrary files
• Retrieval of application configuration information (DB credentials, etc.)
• OS-level operations beyond application permission boundaries

Although administrator privileges are required, this is a design issue where the impact extends from the application layer to the OS layer, and the impact is considered significant.

---

Recommended Fix

Primary Recommendation

• Do not accept the PHP executable path from user input
• Fix the PHP executable on the…

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.

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.

Summary

In the core update functionality of baserCMS, some parameters sent from the admin panel are passed to the exec() function without proper validation or escaping. This issue allows an authenticated CMS administrator to execute arbitrary OS commands on the server (Remote Code Execution, RCE).

This vulnerability is not a UI-level issue such as screen manipulation or lack of CSRF protection, but rather stems from a design that directly executes input values received on the server side as OS commands. Therefore, even if buttons are hidden in the UI, or even if CakePHP's CSRF/FormProtection (SecurityComponent) ensures that only legitimate POST requests are accepted, an attack is possible as long as a request containing a valid token is processed within an administrator session.

---

Vulnerability Information

| Item | Details | | ---- | ------- | | CWE | CWE-78: Improper Neutralization of Special Elements used in an OS Command | | Impact | Remote Code Execution (RCE) | | Severity | Critical | | Attack Requirements | Administrator privileges required | | Reproducibility | Reproducible (confirmed multiple times) | | Test Environment | baserCMS 5.2.2 (Docker / development environment) |

---

Affected Areas

• Controller
  • PluginsController::get_core_update()
• Service
  • PluginsService::getCoreUpdate()
• Affected Endpoint
  • /baser/admin/baser-core/plugins/get_core_update

---

Technical Details

Vulnerable Code Flow

PluginsController::get_core_update()
  ↓ Retrieves php parameter from POST data
PluginsService::getCoreUpdate($targetVersion, $php, $force)
  ↓ Concatenates $php into command string without validation or escaping
exec($command)

Relevant Code (Excerpt)

PluginsController.php

$service->getCoreUpdate(
    $request->getData('targetVersion') ?? '',
    $request->getData('php') ?? 'php',
    $request->getData('force'),
);

PluginsService.php

$command = $php . ' ' . ROOT . DS . 'bin' . DS . 'cake.php composer ' .
           $targetVersion . ' --php ' . $php . ' --dir ' . TMP . 'update';

exec($command, $out, $code);

The $php parameter is user input, and none of the following countermeasures are in place:

• Restriction via allowlist
• Validation via regular expression
• Escaping via escapeshellarg() or similar

---

Attack Scenario

1. The attacker logs in as a CMS administrator
2. Sends a POST request to the core update functionality in the admin panel
3. Specifies a string containing OS commands in the php parameter
4. exec() is executed on the server side, running the arbitrary OS command

Example Attack Input (Conceptual)

php=php;id>/tmp/rce_test;#

---

Verification Results (PoC)

Execution Result

$ docker exec bc-php cat /tmp/rce_test
uid=1000(www-data) gid=1000(www-data) groups=1000(www-data)

The above confirms that OS commands can be executed with www-data privileges.

Additional Notes

• Reproducible through the legitimate flow in the admin panel (browser)
• Succeeds even with CSRF/FormProtection tokens included in a legitimate request
• Failure cases (400/403) have also been investigated and differentiated
• Confirmed reproducible via resending HTTP requests with tools such as curl (resending the same request containing valid tokens)

---

Impact

If this vulnerability is exploited, the following becomes possible:

• Retrieval of server information
• Reading/writing arbitrary files
• Retrieval of application configuration information (DB credentials, etc.)
• OS-level operations beyond application permission boundaries

Although administrator privileges are required, this is a design issue where the impact extends from the application layer to the OS layer, and the impact is considered significant.

---

Recommended Fix

Primary Recommendation

• Do not accept the PHP executable path from user input
• Fix the PHP executable on the…