Skip to content

Craft CMS: Sensitive File Disclosure / Server-Side File Read

Moderate severity GitHub Reviewed Published Jun 16, 2026 in craftcms/cms • Updated Jul 6, 2026

Package

composer craftcms/cms (Composer)

Affected versions

>= 4.0.0-RC1, < 4.18.0
>= 5.0.0-RC1, < 5.10.0

Patched versions

4.18.0
5.10.0

Description

The dataUrl() Twig function is included in Craft’s Twig sandbox allowlist, allowing any control panel user granted the utility:system-messages permission to embed a file-reading payload into system email templates. When those emails are sent, the server reads the target file and returns its contents as a base64-encoded data URL embedded in the email body. The .env file, which typically contains the database password, CRAFT_SECURITY_KEY, and third-party API keys, passes all of Craft’s existing dataUrl() protection checks and is fully exfiltrated. Obtaining CRAFT_SECURITY_KEY enables an attacker to forge session tokens and escalate to full admin account takeover.

Details

Affected versions: Craft CMS 4.x, 5.x (confirmed against 5.9.19)

The vulnerability arises from the combination of three code facts:

  1. dataUrl is in the Twig sandbox allowlist
    src/config/twig-sandbox.php, line 115:
    php'allowedFunctions' => [
    ...
    'dataUrl', // ← allows file reading inside sandboxed templates
    ...
    ],

  2. Html::dataUrl() does not block dotfiles
    src/helpers/Html.php, lines 1065–1090. The function applies four checks before reading a file:

Must be within the project root .env is at the root
Must not be in a system directory (config/, vendor/, storage/, templates/) .env is not
Must not be a .php file .env has no extension
File must exist .env always exists in a Craft install

There is no check for dotfiles or specifically for .env. All four checks pass silently and file_get_contents() is called, with the result returned as data:text/plain;base64,....

  1. System message body is rendered via renderSandboxedString()
    src/mail/Mailer.php, lines 181–183:
    php$subject = $view->renderSandboxedString($systemMessage->subject, $variables);
    $textBody = $view->renderSandboxedString($systemMessage->body, $variables);
    $htmlBody = $view->renderSandboxedString($systemMessage->body, $variables, escapeHtml: true);

Any body content saved to a system message is executed inside the Twig sandbox when the email renders. Because dataUrl is in allowedFunctions, the sandbox policy permits its execution without restriction.

Access control: The utility:system-messages permission is a non-admin CP permission grantable to any user group via Settings > Users > Groups. It is not restricted to admins.

Impact

Vulnerability type: Sensitive File Disclosure / Server-Side File Read
Who is impacted: Any Craft CMS 4.x or 5.x installation where at least one non-admin control panel user has been granted the utility:system-messages permission, and email sending is configured.

Resources:

References

@angrybrad angrybrad published to craftcms/cms Jun 16, 2026
Published by the National Vulnerability Database Jul 2, 2026
Published to the GitHub Advisory Database Jul 6, 2026
Reviewed Jul 6, 2026
Last updated Jul 6, 2026

Severity

Moderate

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 Present
Privileges Required Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity None
Availability None
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:P/PR:L/UI:N/VC:H/VI:N/VA:N/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.
(18th percentile)

Weaknesses

Exposure of Sensitive Information to an Unauthorized Actor

The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. Learn more on MITRE.

CVE ID

CVE-2026-55792

GHSA ID

GHSA-287w-mxq6-x2cp

Source code

Credits

Loading Checking history
See something to contribute? Suggest improvements for this vulnerability.