GHSA-8737-2x9g-xjj7 EGroupware has Authenticated RCE via Malicious eTemplate Upload

• Packagist egroupware/egroupware: >= 26.0.20251208, < 26.4.20260413 → fixed in 26.4.20260413 • Packagist egroupware/egroupware: < 23.1.20260601 → fixed in 23.1.20260601

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. ------------------------------------------------------------------------ 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('$name = "$row`id`";'); // 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 ------------------------------------------------------------------------ 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 /dev/null`"/> ``` 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:///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 = "$row`touch /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. ------------------------------------------------------------------------ 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) ------------------------------------------------------------------------ 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-metal, VM, or custom container deployments without this hardening are fully vulnerable.