CVE-2026-42857 Details
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.
A stored CSS injection vulnerability has been identified in the Open edX Platform, specifically in versions starting from 'sumac'. The issue arises in the HTML sanitizer function 'clean_thread_html_body()', which is responsible for processing user-generated content in discussion posts before it is sent out in email notifications. The sanitizer fails to remove '<style>' tags, allowing enrolled students to inject arbitrary CSS. This injected CSS is rendered in email notifications using Django's 'safe' template filter, enabling email tracking (disclosure of IP addresses), content spoofing, and phishing attacks. The vulnerability has been patched in the 'ulmo', 'verawood', and 'master' versions.
Users can update to the 'ulmo', 'verawood', or 'master' versions of the Open edX Platform to address this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed May 13, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/openedx/openedx-platform/security/advisories/GHSA-4xv3-5j4x-q8g4 | CISA-ADP | ExploitVendor Advisory |
| https://github.com/openedx/openedx-platform/commit/cddc25cd791bb78f76833896e4778f668861df12 | [email protected] | Patch |
| https://github.com/openedx/openedx-platform/security/advisories/GHSA-4xv3-5j4x-q8g4 | [email protected] | ExploitVendor Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-79 | Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| openedx openedx | < 2026-04-24 |
CPE
Remediation
| |
Change History
5 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| May 13, 2026 | CVE Modified | CISA-ADP |
| May 13, 2026 | Initial Analysis | [email protected] |
| May 11, 2026 | New CVE Received | [email protected] |