CVE-2026-73679
Received Received - Intake

Authenticated RCE in ImpressCMS Custom Tag Module via PHP Payload

Publication date: 2026-08-14

Last updated on: 2026-08-14

Assigner: VulnCheck

Description
ImpressCMS contains an authenticated remote code execution vulnerability in the custom tag module that allows authenticated administrators to execute arbitrary PHP code by storing a malicious payload in a custom tag with PHP type enabled. The application decodes HTML-encoded content via undoHtmlSpecialChars() before passing it to eval() in the renderWithPhp() method, bypassing HTML Purifier sanitization, and the payload is triggered on every frontend page load through the preload event system.

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Meta Information

Published
2026-08-14
Last Modified
2026-08-14
Generated
2026-08-14
AI Q&A
2026-08-14
EPSS Evaluated
N/A
NVD
CVE-2026-73679
EUVD
EUVD-2026-58789

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
impresscms impresscms to 2.0.3 (exc)
impresscms impresscms *

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-94 The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.

Attack-Flow Graph

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Executive Summary

This is an authenticated remote code execution (RCE) vulnerability in ImpressCMS versions 2.0.3 and earlier. It allows administrators with access to inject malicious PHP code via a custom tag with PHP type enabled. The application decodes HTML-encoded content before passing it to eval(), bypassing HTML Purifier sanitization. The payload executes on every frontend page load through the preload event system.

Detection Guidance

Check for ImpressCMS installations with version 2.0.3 or earlier. Look for suspicious PHP custom tags in the database that contain PHP code. Review server logs for repeated eval() function calls or unusual PHP execution patterns. Inspect frontend page loads for unexpected web shell activity or unauthorized file writes.

Impact Analysis

An attacker with administrator privileges can execute arbitrary PHP code on the server. This could lead to full system compromise, including writing web shells, executing commands, and gaining persistent access. The impact includes loss of confidentiality, integrity, and availability of the system.

Compliance Impact

This vulnerability can lead to unauthorized access and data breaches, violating GDPR and HIPAA requirements for data protection and confidentiality. It may result in non-compliance due to potential exposure of sensitive data and lack of proper access controls.

Mitigation Strategies

Upgrade ImpressCMS to a patched version beyond 2.0.3. Disable PHP-type custom tags in the admin panel. Restrict administrative access to trusted users only. Implement strict input validation and output encoding. Monitor for unauthorized PHP file creation or execution.

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