CVE-2026-123311 in IntelliJ IDEA
Summary
by MITRE • 11/06/2026
In JetBrains IntelliJ IDEA before 2026.3, 2026.2.4 command execution via a hidden run control in the Markdown preview was possible
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Analysis
by VulDB Data Team • 11/06/2026
The vulnerability identified involves a critical security flaw within the Markdown preview functionality of JetBrains IntelliJ IDEA versions prior to 2026.3 and specifically affecting version 2026.2.4. This issue stems from an improper neutralization of special elements, commonly categorized under CWE-79 or related input validation failures depending on the specific implementation details of how external content is processed within the integrated development environment. The core technical flaw lies in the handling of hidden run controls embedded within Markdown files. When a user opens a Markdown document containing these concealed commands, the IDE's preview engine processes them without adequate sanitization or isolation mechanisms that would prevent arbitrary code execution on the host system.
This vulnerability allows an attacker to achieve command execution by crafting a malicious Markdown file that includes specially formatted hidden run controls. These controls are designed to be invisible during standard viewing but become active when rendered in the IDE's preview pane. Upon rendering, the underlying engine interprets these commands as executable instructions rather than static text or formatting markers. This bypasses typical user expectations where Markdown is treated primarily as a documentation format with limited interactive capabilities. The lack of proper sandboxing for this specific feature means that any command specified within these hidden controls runs with the same privileges as the IntelliJ IDEA process itself, potentially granting an attacker full control over the development environment and connected systems if the IDE is run with elevated permissions.
The operational impact of this vulnerability is severe, particularly in collaborative software development environments where Markdown files are frequently shared via version control systems such as Git or through email attachments. A developer who opens a maliciously crafted README file, documentation set, or configuration guide could inadvertently trigger arbitrary code execution on their machine. This can lead to data exfiltration, installation of persistent backdoors, modification of source code repositories, or the use of the compromised workstation as a pivot point for further attacks within the corporate network. The stealthy nature of hidden run controls exacerbates the risk because users are unlikely to suspect that static documentation files contain executable payloads, making social engineering attacks significantly more effective.
Mitigation strategies primarily involve upgrading JetBrains IntelliJ IDEA to version 2026.3 or later, where this specific handling of Markdown preview commands has been corrected. Until an upgrade is feasible, developers should exercise extreme caution when opening Markdown files from untrusted sources and avoid using the built-in preview feature for such documents. Instead, relying on external, sandboxed markdown renderers can reduce exposure. From a defensive posture perspective, organizations should implement application whitelisting to restrict arbitrary command execution within IDE processes and ensure that endpoint detection and response solutions are configured to monitor for suspicious process creation events originating from development tools. This incident highlights the importance of treating all user-supplied content with skepticism, even in formats traditionally considered safe like Markdown, aligning with ATT&CK techniques related to Command and Scripting Interpreter abuse and Initial Access via malicious files.