CVE-2026-42857

Open edX Platform: Stored CSS Injection in Email Notifications via Incomplete HTML Sanitization

Published May 11, 2026 CVSS 3.1 · 4.6 Medium EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
First Time appeared Openedx openedx
CPEs cpe:2.3:a:openedx:openedx:*:*:*:*:*:*:*:*
Vendors & Products Openedx openedx
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Openedx
Openedx openedx-platform
Vendors & Products Openedx
Openedx openedx-platform
Type Values Removed Values Added
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.
Title Open edX Platform: Stored CSS Injection in Email Notifications via Incomplete HTML Sanitization
Weaknesses CWE-79
References
Metrics cvssV3_1

{'score': 4.6, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
May 13, 2026, 2:40 PM
Reserved
Apr 30, 2026, 4:44 PM
Status
Modified
Published
May 11, 2026, 6:16 PM
Modified
Oct 26, 2026, 6:10 PM