EGroupware has Authenticated RCE via Malicious eTemplate Upload
Summary
An authenticated administrator can achieve OS-level Remote Code Execution (RCE) by uploading a malicious eTemplate XML file (.xet) to the VFS /etemplates mount.
The Widget::expand_name() method passes template widget attribute values directly into a PHP eval() call with only double-quote escaping applied - backtick characters are not escaped.
In PHP, backticks inside a double-quoted eval() string execute shell commands. This allows an admin-level user to escalate from web
application access to arbitrary OS command execution on the server.
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Details
The vulnerability is located in api/src/Etemplate/Widget.php, Widget::expand_name(): (lines 703–728)
The method is designed to expand PHP variables (e.g., $row, $col,$cont[id]) in widget attribute values for auto-repeat grids. The eval() is triggered whenever $name contains a $ character (line 706). The only sanitization applied before the eval is:
``` php
str_replace('"', '\\"', $name)
```
This escapes double quotes only. Backtick characters are not escaped. In PHP, backticks inside a double-quoted string in eval() are treated as shell execution operators — equivalent to shell_exec(). A widget id of $row\id`` produces:
```
eval('$name = "$rowid";'); // executes shell command: id
```
expand_name() is called from:
form_name()expand_widget()set_attrs()Template::run()
The /etemplates VFS path is created exclusively for admin users — it is chgrp'd to Admins and chmod'd to 075 (Admins group has full rwx): class.filemanager_admin.inc.php:95-106
Custom templates in /etemplates take precedence over built-in filesystem templates, meaning a malicious template can silently override any existing application template.
Mitigating factor: The official Docker deployment sets disable_functions = exec,passthru,shell_exec,system,proc_open,popen in php.ini, which also blocks PHP backtick execution (backticks internally call shell_exec). Non-Docker or non-hardened deployments without this php.ini setting are fully vulnerable. Dockerfile:47
The current master branch in api/setup/setup.inc.php, confirming the vulnerability is present in the latest code as of today. setup.inc.php:14-17
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Proof of Concept (PoC)
Prerequisites
- Admin account
- Non-Docker deployment, or Docker deployment where disable_functions has been removed/modified in php.ini
Step 1 — Mount /etemplates:
Log in as admin, navigate to Admin → Filemanager → VFS Mounts, and click "Install custom templates". This executes the code in filemanager_admin.inc.php that mounts /etemplates with Admins-group write access.
Step 2 — Upload malicious template:
Create a file named index.xet with the following content:
``` xml
<?xml version="1.0" encoding="UTF-8"?>
<overlay>
<template id="admin.index">
<grid>
<columns><column/></columns>
<rows>
<row>
<textbox id="$rowtouch /tmp/pwned_egw 2>/dev/null"/>
</row>
</rows>
</grid>
</template>
</overlay>
```
Upload this file to /etemplates/admin/templates/default/index.xet via the VFS filemanager.
Step 3 — Trigger execution:
Navigate to the EGroupware admin panel:
```
https://<target>/egroupware/index.php?menuaction=admin.admin_ui.index
```
When the template is loaded and beforeSendToClient() runs, form_name() calls expand_name() with $name = '$row\touch /tmp/pwned_egw 2>/dev/null'and$row = 0. The eval becomes:
```
eval('$name = "$rowtouch /tmp/pwned_egw 2>/dev/null";');
```
PHP executes the backtick expression as a shell command.
Step 4 — Verify:
Check that /tmp/pwned_egw was created on the server. For a more impactful demonstration, replace touch /tmp/pwned_egw with id > /tmp/pwned_egw to capture the web server's OS user identity.
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Impact
Authenticated Remote Code Execution (RCE) via eval() with unsanitized shell metacharacters.
Who is impacted: Any EGroupware installation where:
1. An admin account is compromised or a malicious admin exists, AND
2. The server is not running with disable_functions blocking shell_exec (i.e., non-Docker or misconfigured deployments)
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Severity
The vulnerability allows escalation from EGroupware admin-level web access to arbitrary OS command execution as the web server user (typically www-data). From there, an attacker can read configuration files (including database credentials), pivot to other services, or establish persistence. This is not exploitable by regular (non-admin) users. The official Docker deployment is not affected due to disable_functions, but bare
