External risk intelligence

JetBrains CLion Safe Mode Code Execution via Meson Project Settings

CVE advisorySeverity: CRITICAL (CVSS 9.6)

CVE-2026-123831

JetBrains CLion is an integrated development environment (IDE) used locally by developers. The vulnerability exists within Meson project settings, which requires a user to open a project file. IDEs are developer-centric, desktop-based applications that are not designed to be exposed to the public internet or function as internet-facing services.

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A vulnerability has been identified in JetBrains CLion that could allow for code execution within Safe Mode when processing Meson project settings. This could potentially impact systems that use this specific development environment for project management. The main concern at this time is to confirm if this technology is in use within our organization and to what extent.

Vulnerability allows code execution in a development tool.
Affects specific developer workflows and project settings.
Confirm relevance and exposure within our environment.

Attack Path

How an attacker could exploit the issue

An attacker could trick a developer into opening a malicious project file in JetBrains CLion. This could allow the attacker to execute arbitrary code on the developer's machine, potentially leading to wider system compromise if the developer has elevated privileges.

Entry condition: Developer opens a malicious project file.
Trigger point: Meson project settings parsing.
Resulting risk: Arbitrary code execution.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an attacker to execute arbitrary code within the CLion IDE when a user opens a malicious Meson project file. This could lead to the compromise of the developer's local machine and any sensitive information accessible by the IDE.

Local development environment.
Opening a specially crafted project file.
Potential for code execution on developer machine.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in JetBrains CLion's Safe Mode, exploitable via Meson project settings, primarily impacts development environments. Application owners or development team leads are typically responsible for managing IDEs and their configurations. The first practical step is for these teams to identify which developers use the affected version, assess the risk based on whether they open untrusted Meson projects, and then plan for an upgrade outside of standard maintenance windows if critical.

Development teams own this issue.
Verify affected developer environments.
Plan controlled upgrade process.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is JetBrains CLion?

CLion is a cross-platform integrated development environment (IDE) designed for software developers writing code in C and C++. It provides tools like intelligent code completion, refactoring, and project management—specifically supporting build systems like Meson—to streamline development on local desktop workstations.

How does CWE-829 describe this vulnerability?

This CVE involves CWE-829, which refers to the inclusion of functionality from an untrusted control sphere. In simpler terms, the IDE improperly trusts or executes instructions contained within a project configuration file, allowing external, malicious code to run when it should be restricted by Safe Mode.

Do I need to worry if I am not using Meson projects?

No. The vulnerability is triggered specifically during the parsing of Meson project settings. If your development workflow does not involve importing or opening Meson-based projects in the affected CLion versions, the conditions required to trigger this code execution path are not present.

Is my JetBrains CLion instance internet-facing?

According to Halo Surface Signal, CLion is a desktop-based application used locally and is not designed to function as an internet-facing service. The risk is localized to your machine, primarily when a user is tricked into opening a malicious file, rather than being reachable via network scans.

When should I update my CLion software?

You should prioritize identifying developers using versions earlier than 2026.2 or 2026.1.4. Once identified, plan a controlled update to a patched version. Focus your effort on teams that frequently work with external or untrusted project files, as this is the primary vector for the flaw.

References

www.jetbrains.com/privacy-security/issues-fixed/

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.