---
id: "CVE-2026-123309"
page: "https://infrastack.ai/live/CVE-2026-123309"
kind: "vulnerability"
aliases: ["CVE-2026-123309"]
title: "IntelliJ IDEA: stored XSS via Markdown preview on built-in web server"
severity: "medium"
cvss: 6.1
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["intellij-idea", "jetbrains", "markdown", "package", "xss"]
not_affected_if: ["updated-ide-version"]
published_at: "2026-11-06T11:17:10+00:00"
first_seen_at: "2026-11-06T11:41:25+00:00"
updated_at: "2026-11-06T11:42:23+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-123309", "first_seen_at": "2026-11-06T11:41:25+00:00"}]
exploit_sources: []
---

# IntelliJ IDEA: stored XSS via Markdown preview on built-in web server

Link for people: https://infrastack.ai/live/CVE-2026-123309 (this .md is for agents)

In JetBrains IntelliJ IDEA before 2026.3 and 2026.2.4, a Markdown preview served by the built-in web server could store malicious script. A script running in the browser of a developer who views that preview could act with that developer's access.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the IntelliJ IDEA version under Help > About and compare it with `2026.3` and `2026.2.4`
- Confirm whether the built-in web server is in use for Markdown preview in your IDE setup

## Fix

- IntelliJ IDEA: move to `2026.3` or `2026.2.4`, per the sources' affected range

## Timeline

- 2026-11-06T11:41:25+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-123309

## From the sources

In JetBrains IntelliJ IDEA before 2026.3, 
2026.2.4 stored XSS was possible on the built-in web server via Markdown preview

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_