Quick answers
- Is CVE-2026-123309 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-123309 being exploited in the wild.
- How severe is CVE-2026-123309?
- Medium severity, with a CVSS score of 6.1, published 6 November 2026.
- Which products and versions are affected?
- Jetbrains IntelliJ IDEA before 2026.3, 2026.2.4.
- Is there a fix for CVE-2026-123309?
- Yes: fixed in IntelliJ IDEA 2026.3, 2026.2.4. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-123309 attacked?
- It is attacked over the network, in a web application.
- Am I affected by CVE-2026-123309?
- Check whether you run Jetbrains IntelliJ IDEA at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- Fixed in: IntelliJ IDEA 2026.3, 2026.2.4
Technical details
A stored XSS vulnerability exists in IntelliJ IDEA's Markdown preview functionality on the built-in web server, allowing attackers to inject malicious JavaScript into Markdown documents. The vulnerability requires network access to the web server and the ability to craft or control Markdown content, but no authentication is required. Successful exploitation could result in arbitrary JavaScript execution within the IDE's preview context.
Affected products
- JetBrains IntelliJ IDEA before 2026.3, 2026.2.4
Timeline
- 2026-11-06: disclosed