# CVE-2026-123854: JetBrains PyCharm code execution via crafted Jupyter notebook widget

Source: https://junglewise.ai/threats/cve-2026-123854-in-jetbrains-pycharm-before-2026-3-code-execution-was-possible  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-06. Updated: 2026-11-06  
License: CC BY 4.0 with a link back

CVE-2026-123854 · Severity: medium · CVSS 5.5 · Published 2026-11-06

JetBrains PyCharm is a Python IDE used by developers to write and test code. A vulnerability allows an attacker to execute arbitrary code even when PyCharm's Safe Mode is enabled, by crafting a malicious Jupyter notebook with a malicious widget module. An attacker who tricks a developer into opening a crafted notebook gains the ability to run code with the privileges of the PyCharm process.

Technologies: [Jetbrains PyCharm](https://junglewise.ai/threats/technologies/pycharm). Vendors: [Jetbrains](https://junglewise.ai/threats/vendors/jetbrains).

## Quick answers

**Is CVE-2026-123854 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-123854 being exploited in the wild.

**How severe is CVE-2026-123854?** Medium severity, with a CVSS score of 5.5, published 6 November 2026.

**Which products and versions are affected?** Jetbrains PyCharm before 2026.3.

**Is there a fix for CVE-2026-123854?** Yes: fixed in PyCharm 2026.3. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-123854 attacked?** It is attacked with local access, in a web application.

**Am I affected by CVE-2026-123854?** Check whether you run Jetbrains PyCharm 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 PyCharm 2026.3

## Technical details

Safe Mode bypass in JetBrains PyCharm allows arbitrary code execution through a crafted Jupyter notebook widget module. The vulnerability affects the Jupyter notebook integration component and requires user interaction (opening a malicious notebook file). An attacker can execute arbitrary code within the IDE process despite Safe Mode protections being enabled.

## Affected products

- JetBrains PyCharm before 2026.3

## Timeline

- 2026-11-06: disclosed
- 2026-11-06: patched

## References

- [https://www.jetbrains.com/privacy-security/issues-fixed/](https://www.jetbrains.com/privacy-security/issues-fixed/)

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