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Craft CMS: Authenticated RCE through Twig sandbox escape

High severity GitHub Reviewed Published Jul 25, 2026 in craftcms/cms • Updated Sep 1, 2026

Package

composer craftcms/cms (Composer)

Affected versions

>= 5.0.0-RC1, < 5.10.7
>= 4.0.0-RC1, < 4.18.3

Patched versions

5.10.7
4.18.3

Description

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.

Impact

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().

References

@angrybrad angrybrad published to craftcms/cms Jul 25, 2026
Published to the GitHub Advisory Database Aug 6, 2026
Reviewed Aug 6, 2026
Last updated Sep 1, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(43rd percentile)

Weaknesses

Protection Mechanism Failure

The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product. Learn more on MITRE.

CVE ID

CVE-2026-72781

GHSA ID

GHSA-f5wm-88jv-g5hx

Source code

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