CVE-2026-42857: Open edX Platform enables the authoring and delivery of online learning at any scale. The HTML sanitizer clean_thread_html_body() used for discussion…

PriorityP429medium5.4CVSS 3.1

AVNACLPRLUIRSCCLILAN

EPSS

0.21%

11.3th percentile

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 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.

Affected

3 ranges

Vendor	Product	Version range	Fixed in
openedx	openedx	< 2026-04-24	2026-04-24
openedx	openedx-platform	< cddc25cd791bb78f76833896e4778f668861df12	cddc25cd791bb78f76833896e4778f668861df12
openedx	openedx-platform	—	—

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