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Vulnerability record · CVE-2026-42857 · published 11 May 2026

CVE-2026-42857: Openedx cross-site scripting vulnerability

Openedx · Openedx

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.

5.4 CVSS 3.1 Medium EPSS 0.25% · top 85.6% CWE-79 · Cross-site scripting
5.4CVSS 3.1 base score
0.25%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
3References, 2 tagged exploit
17 Jun 2026Last modified by NVD

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.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/openedx/openedx-platform/commit/cddc25cd791bb78f76833896e4778f668861df12 Patch
https://github.com/openedx/openedx-platform/security/advisories/GHSA-4xv3-5j4x-q8g4 ExploitVendor Advisory
https://github.com/openedx/openedx-platform/security/advisories/GHSA-4xv3-5j4x-q8g4 ExploitVendor Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-42857), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.