CVE-2026-42857

Name: CVE-2026-42857
Creator: NVD / NIST
Published: 2026-05-11T18:16:36.13+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.4/10EPSS 0.21%

Last modified Jun 17, 2026

CVE-2026-42857 is a medium-severity vulnerability rated 5.4/10 on the CVSS scale. Open edX Platform enables the authoring and delivery of online learning at any scale. The HTML sanitizer clean_thread_html_body() used for discussion notification emails fails to remove <style> tags from user-generated discussion post content. EPSS estimates a 0.21% chance of exploitation in the next 30 days.

Description

Open edX Platform enables the authoring and delivery of online learning at any scale. The HTML sanitizer clean_thread_html_body() used for discussion notification emails fails to remove <style> tags from user-generated discussion post content. This content is rendered with Django's |safe template filter in email notification templates, allowing any enrolled student to inject arbitrary CSS into email notifications sent to other users. This enables email tracking (IP address disclosure), content spoofing, and phishing attacks. This vulnerability is fixed with commit cddc25cd791bb78f76833896e4778f668861df12.

Metrics

CVSS 3.1

5.4/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

EPSS Probability

0.21%

11.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-79

Affected Software

Vendor	Product	Versions
Openedx	Openedx	< 2026-04-24

References

https://github.com/openedx/openedx-platform/commit/cddc25cd791bb78f76833896e4778f668861df12Patch
https://github.com/openedx/openedx-platform/security/advisories/GHSA-4xv3-5j4x-q8g4Exploit, Vendor Advisory
https://github.com/openedx/openedx-platform/security/advisories/GHSA-4xv3-5j4x-q8g4Exploit, Vendor Advisory

Timeline

Published: May 11, 2026
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2026-42857?

How severe is CVE-2026-42857?

CVE-2026-42857 has a CVSS score of 5.4/10 (MEDIUM severity). The EPSS model estimates a 0.21% probability of exploitation in the next 30 days.

How do I fix CVE-2026-42857?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-42857?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST