CVE-2026-65693: Microweber CMS RCE Vulnerability

CVE-2026-65693 Overview

CVE-2026-65693 is a server-side template injection (SSTI) vulnerability affecting Microweber CMS through version 2.0.20. Authenticated administrators can inject Twig expressions into mail templates to achieve arbitrary operating system command execution. The TwigView::render() method operates without SandboxExtension or a SecurityPolicy, allowing dangerous filters such as filter('system') to execute. Mail template bodies are stored unsanitized in the database, causing injected payloads to run on every subsequent application event that dispatches mail.

Critical Impact
Successful exploitation grants attackers arbitrary OS command execution in the context of the web application, enabling full server compromise, data exfiltration, and lateral movement.

Affected Products

Microweber CMS versions through 2.0.20
Deployments using the default unsandboxed Twig mail template rendering path
Instances where administrator accounts are accessible to untrusted or compromised users

Discovery Timeline

2026-07-24 - CVE-2026-65693 published to NVD
2026-07-28 - Last updated in NVD database

Technical Details for CVE-2026-65693

Vulnerability Analysis

The vulnerability is a code injection flaw classified under [CWE-94]. Microweber CMS renders mail templates through a Twig environment instantiated in TwigView::render(). This environment omits both SandboxExtension and any configured SecurityPolicy, leaving the full Twig expression language exposed to template content.

An authenticated administrator can modify mail template bodies through the CMS backend. Because these bodies are persisted to the database without sanitization, any embedded Twig expression is evaluated during rendering. The filter function permits calling arbitrary PHP callables, including system, which yields OS command execution.

Each subsequent mail dispatch triggered by normal application events re-renders the poisoned template, providing persistent execution on the server without further attacker interaction.

Root Cause

The root cause is an insecure Twig environment configuration in the mail rendering pipeline. Twig is intended to run untrusted templates only inside a sandbox that whitelists tags, filters, functions, and methods. Microweber renders administrator-controlled template content in a fully unrestricted environment, treating stored template bodies as trusted code.

Attack Vector

An attacker with administrative credentials edits a mail template through the Microweber administration interface and inserts a Twig expression such as one invoking the filter('system') construct with an arbitrary shell command. The payload is written to the database. When the application later dispatches a mail using that template, TwigView::render() evaluates the expression and the operating system executes the embedded command under the web server user.

The vulnerability mechanism and a proof-of-concept payload are documented in the VulnCheck Advisory on Microweber CMS and the GitHub Gist Exploit Code.

Detection Methods for CVE-2026-65693

Indicators of Compromise

Mail template records in the Microweber database containing Twig delimiters such as {{ combined with filter, system, exec, passthru, or shell_exec tokens.
Unexpected child processes spawned by the PHP-FPM or web server process, such as sh, bash, curl, wget, or nc.
Outbound network connections initiated by the web server user to unknown hosts shortly after mail dispatch events.
New or modified files under the Microweber web root, especially PHP files placed in userfiles/ or writable upload directories.

Detection Strategies

Audit the mail templates table for Twig expression syntax and unexpected function references. Alert on any diff that introduces {{ ... }} blocks in mail bodies.
Monitor process ancestry to identify shell interpreters or network utilities launched by the web server process, which is anomalous for a normal CMS workload.
Correlate administrator authentication events with subsequent modifications to mail templates and later command execution telemetry.

Monitoring Recommendations

Enable PHP disable_functions logging and web application audit logging for the Microweber administration endpoints related to mail template configuration.
Forward web server, PHP-FPM, and OS process telemetry to a centralized analytics platform to detect the injection-to-execution chain.
Track administrator account activity, including logins from new IP addresses and modifications to template resources, and alert on deviations from baseline behavior.

How to Mitigate CVE-2026-65693

Immediate Actions Required

Restrict access to the Microweber administration interface using IP allowlisting or a VPN until a patched version is deployed.
Rotate all administrator credentials and enforce multi-factor authentication on administrative accounts.
Review existing mail templates for Twig expressions and remove any content that was not authored by a trusted administrator.
Inspect the host for signs of prior exploitation, including unexpected processes, cron entries, and web shells.

Patch Information

At the time of publication, no fixed version is referenced in the NVD entry for Microweber CMS. Consult the VulnCheck Advisory on Microweber CMS and the Microweber project for the latest remediation guidance and upgrade instructions. Track the vendor repository for a release that enables SandboxExtension and a strict SecurityPolicy in TwigView::render().

Workarounds

Limit the administrator role to a minimal set of trusted operators and audit the roster regularly.
Apply a temporary application patch that wraps TwigView::render() with a Twig SandboxExtension configured with an allowlist that excludes the filter function and PHP callables.
Run the web server process as an unprivileged user with open_basedir restrictions and disable_functions entries covering system, exec, passthru, shell_exec, and proc_open.
Deploy a web application firewall rule that blocks request payloads containing Twig control sequences submitted to mail template endpoints.

bash

# Example php.ini hardening to reduce OS command execution impact
disable_functions = system,exec,passthru,shell_exec,proc_open,popen,pcntl_exec
open_basedir = /var/www/microweber:/tmp