The Twig sandbox mechanism in Craft CMS is configured to allow dangerous functionality from the Yii framework, leading to authenticated RCE in a manner similar to previously disclosed vulnerabilities.
The Twig sandbox in Craft CMS works by implementing Twig's SecurityPolicyInterface. The resulting SecurityPolicy class implements the checkMethodAllowed and checkPropertyAllowed methods of the interface. The implementations compare whether the called method or property is in a configured allowlist or is marked with the AllowedInSandbox attribute.
Additionally, SecurityPolicy allows the allowlisting of whole classes, which is shorthand for allowing all methods and properties of that class to be called. Both the allowlists for tags, filters, variables, methods, properties, and classes, as well as the AllowedInSandbox attribute mechanism, are preconfigured by Craft CMS to allow user-defined templates to use core functionality unimpeded. Additionally, Craft CMS project developers can add more to the allowlists or mark their custom methods and so on as safe with AllowedInSandbox.
The SecurityPolicy class's allowlisting mechanism is potentially dangerous, as it allows all methods and properties on an object of the allowed class. This means that the checked object can be a subclass and be allowed. And it means that the allowed methods and properties can be defined on any class of the class hierarchy of the object, which does not have to be the allowed class itself.
Craft CMS uses the AllowedInSandbox attribute to mark the ElementInterface as safe. The Element class implements this interface and is the base class for many relevant model classes in Craft CMS, like Entry, User, Asset and so on. Additionally, Element extends the craft\base\Component class. Going up the class hierarchy of craft\base\Component, eventually the class yii\base\Component is reached, which is located in the Yii framework used by CraftCMS. yii\base\Component is known to contain a dangerous arbitrary function call gadget which leads to previously disclosed RCE vulnerabilities in Craft CMS (GHSA-255j-qw47-wjh5, GHSA-2fph-6v5w-89hh, GHSA-7jx7-3846-m7w7, GHSA-qrgm-p9w5-rrfw). Due to lax class allowlisting, this function-call gadget is allowed in the Twig sandbox. This allows sandboxed Twig templates to use known payloads based on the function-call gadget to achieve RCE.
An authenticated attacker with permission to access the control panel can render a malicious Twig template and gain RCE, even if the Twig sandbox is enabled through enableTwigSandbox().
| Software | From | Fixed in |
|---|---|---|
craftcms / cms
|
5.0.0-RC1 | 5.10.7 |
craftcms / cms
|
4.0.0-RC1 | 4.18.3 |
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.