Skip to content

Stored XSS via unescaped Blade directives in display templates

High
dbarzin published GHSA-65p7-pph2-966g Feb 22, 2026

Package

composer dbarzin/mercator (Composer)

Affected versions

< 2026.02.22

Patched versions

2026.02.22

Description

Summary

A stored Cross-Site Scripting (XSS) vulnerability exists in Mercator due to the use of unescaped Blade directives ({!! !!}) in display templates.
An authenticated user with the User role can inject arbitrary JavaScript payloads into fields such as "contact point" when creating or editing entities. The payload is then executed in the browser of any user who views the affected page, including administrators.

Details

Mercator uses Laravel Blade templates to render entity data. Several display templates use the {!! $variable !!} syntax, which renders raw HTML without escaping. While this is intentional for rich-text fields managed by the CKEditor editor, it is also applied to plain-text fields such as the contact point field, which have no legitimate need to contain HTML.

Because no server-side sanitization is performed on user input before storage, an attacker can submit a malicious payload through the standard web interface or directly via the API, bypassing the client-side CKEditor protection entirely.

Attack scenario (User → Admin escalation)

  1. An attacker with a low-privilege User account creates or edits an entity and injects
    a JavaScript payload into the contact point field.
  2. An administrator navigates to the page displaying that entity.
  3. The payload executes in the administrator's browser.
  4. The attacker can exfiltrate the administrator's XSRF-TOKEN and use it to perform
    state-changing requests on behalf of the administrator.

Note: session cookie theft is mitigated by the HttpOnly flag on themercator_session cookie, but CSRF token exfiltration remains a concrete impact.

Affected components

  • All Blade display templates using {!! !!} on user-supplied plain-text fields
  • Confirmed affected field: contact point (contact) on entity pages
  • Other fields using {!! !!} may also be affected (full audit in progress)

Remediation

The fix will be released by 2026-02-22 and includes two layers of defense:

  1. Input sanitization via FormRequest : Integration of mews/purifier (HTMLPurifier) in a BaseFormRequest class. Plain-text fields will be processed with strip_tags(), rich-text fields with Purifier::clean() using a restricted allow-list configuration.

  2. Blade template correction : Systematic replacement of {!! !!} with {{ }} for all fields that do not require HTML rendering.

Credits

This vulnerability was discovered and responsibly disclosed by Hadrien Chauder, penetration tester, who reported it directly to the maintainer before any public disclosure and provided a detailed proof of concept.

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 Passive
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
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:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

CVE ID

CVE-2026-27639

Weaknesses

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Learn more on MITRE.

Credits