CVE-2026-111091 in Junie CLI
Summary
by MITRE • 10/15/2026
In JetBrains Junie CLI before 26.8.3 code execution was possible via an untrusted project's MCP server configuration
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in JetBrains Junie CLI prior to version 26.8.3 represents a critical security flaw rooted in the improper handling of external configurations, specifically those associated with Model Context Protocol (MCP) servers. This issue allows for arbitrary code execution on the host system when an untrusted project is loaded or accessed within the development environment. The core technical deficiency lies in the application's failure to adequately sanitize and validate configuration inputs provided by MCP server definitions before they are processed and executed. By treating these configurations as trusted entities without sufficient verification, the software inadvertently creates a pathway for attackers to inject malicious commands that bypass standard security controls.
From a technical perspective, this vulnerability aligns with CWE-94 Improper Control of Generation of Code (Code Injection). The flaw occurs because the CLI tool parses configuration data from external sources and directly incorporates it into execution contexts without enforcing strict boundaries or sandboxing mechanisms. When an attacker provides a maliciously crafted MCP server configuration within an untrusted project, the application interprets specific fields as executable instructions rather than mere metadata. This misinterpretation enables the injection of shell commands or script executions that run with the privileges of the user invoking the CLI tool. The lack of input validation and the absence of secure coding practices in parsing these external configurations form the basis of this exploit vector, allowing for remote code execution if the configuration is sourced from a compromised or malicious repository.
The operational impact of this vulnerability is severe, as it compromises the integrity and confidentiality of the developer's local environment. An attacker who can influence the project structure or force the loading of an untrusted project containing a poisoned MCP configuration can achieve arbitrary command execution on the victim's machine. This could lead to data exfiltration, installation of persistent backdoors, pivoting into internal networks, or complete system compromise depending on the user privileges under which Junie CLI is executed. Since development tools often have access to sensitive source code and credentials stored in environment variables, this vulnerability poses a significant risk to intellectual property and organizational security posture. It undermines the trust developers place in their integrated development environments and tooling ecosystems.
This incident highlights the growing risks associated with integrating external AI-driven services and protocol-based extensions into local development workflows. The Model Context Protocol is designed to facilitate communication between applications and large language models, but its flexibility introduces complex attack surfaces if not implemented securely. Security teams must recognize that any component accepting input from untrusted sources requires rigorous validation and isolation strategies. The failure to implement these safeguards in the Junie CLI configuration parser demonstrates a gap in secure software development lifecycle practices regarding third-party integrations and dynamic configuration handling.
To mitigate this vulnerability, users are strongly advised to upgrade JetBrains Junie CLI to version 26.8.3 or later immediately upon availability. This update contains patches that enforce stricter validation rules on MCP server configurations, ensuring that only safe and expected parameters are processed during execution. In the interim, developers should exercise extreme caution when working with projects from untrusted sources or repositories where configuration files may have been tampered with. It is recommended to audit project structures for any unusual MCP-related entries before loading them in the IDE. Additionally, organizations should implement network segmentation and least-privilege principles to limit the potential blast radius of such exploits. Regular security training focused on secure coding practices for external integrations can further reduce the likelihood of similar vulnerabilities arising from future updates or extensions.
The ATT&CK framework categorizes this type of vulnerability under techniques related to command and script interpretation, specifically those involving local execution via injected payloads. Understanding these mappings helps in developing more robust detection rules and incident response procedures. Security monitoring should focus on anomalous process creation events originating from development tools, particularly when they involve shell interpreters or scripting engines invoked by unexpected parent processes like IDEs or CLI utilities. By combining technical patches with proactive security hygiene and awareness, organizations can effectively neutralize the threat posed by this code execution flaw in JetBrains Junie CLI.