CVE-2026-78834 in CoAuthors Plugin
Summary
by MITRE • 09/08/2026
A code execution vulnerability exists in CMSimple 5.22 in the CoAuthors plugin. An authenticated low-privileged user who can modify page content and provide controlled imported content can trigger server-side execution by referencing crafted external or uploaded text content through the affected content import feature.
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Analysis
by VulDB Data Team • 09/08/2026
The identified security flaw resides within the CMSimple 5.22 platform, specifically affecting the CoAuthors plugin functionality. This vulnerability is classified as a code injection issue that allows for remote code execution under specific conditions. The root cause lies in how the application handles content imported through its built-in import feature when managed by users with low-level privileges who possess the ability to modify page content. Unlike critical vulnerabilities requiring administrative access, this flaw exploits the trust placed in authenticated but non-privileged users, representing a significant deviation from expected security boundaries where such users should only be able to manipulate text data without affecting server-side execution logic.
Technically, the vulnerability stems from insufficient sanitization or validation of imported content within the CoAuthors plugin. When an attacker provides controlled external or uploaded text content through the affected import mechanism, the application fails to properly neutralize special characters or script elements before processing them for display or storage. This lack of proper input validation allows malicious code payloads embedded in the imported data to be interpreted and executed by the server environment rather than being treated as inert text. The attacker leverages this behavior by crafting specific content that exploits parsing inconsistencies, effectively bypassing standard security controls designed to prevent script injection.
The operational impact of this vulnerability is severe due to its potential for full system compromise. An authenticated low-privileged user can achieve arbitrary code execution on the web server hosting CMSimple. This capability enables the attacker to perform a wide range of malicious activities including but not limited to stealing sensitive data, modifying application configurations, installing backdoors, or pivoting to attack other systems within the internal network. The ability for lower-privilege accounts to escalate their impact significantly increases the risk surface area, as it requires only basic authentication credentials rather than high-level administrative access, making exploitation more feasible and likely in environments with numerous user accounts.
This vulnerability aligns closely with Common Weakness Enumeration (CWE) identifiers such as CWE-94 Improper Control of Generation of Code or Script, commonly known as code injection, and potentially CWE-79 if the execution involves cross-site scripting variants depending on the specific server-side interpretation mechanism. In terms of tactical mapping within the MITRE ATT&CK framework, this behavior corresponds to techniques involving command and script interpreter abuse for initial access or persistence. The exploitation path demonstrates how improper input validation in content management systems can lead to critical security breaches even when restricted by user roles.
Mitigation strategies should focus on immediate remediation through software updates provided by the vendor if available, ensuring that patches addressing this specific flaw are applied promptly. In cases where an update is not immediately accessible, administrators must implement strict access controls limiting who can utilize content import features and enforce rigorous input validation at the application level to sanitize all imported data before processing. Additionally, deploying a Web Application Firewall with rules tuned to detect code injection patterns in POST requests related to content imports can provide an additional layer of defense. Regular security audits and penetration testing focused on privilege escalation paths are recommended to identify similar weaknesses across other plugins or core functionalities within the CMSimple ecosystem.