Vulnerability · Published May 11, 2026 · Assigned by GitHub_M

CVE-2026-42857Open edX Platform: Stored CSS Injection in Email Notifications via Incomplete HTML Sanitization

Medium 4.6

In plain English

A medium-severity cross-site scripting in openedx-platform from openedx. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 8% of all known vulnerabilities).

Severity (CVSS 3.1)4.6Medium

Exploit odds (30 days)0.2%top 92.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official 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.

Affected products (as reported)

Vendor	Product	Versions
openedx	openedx-platform	< cddc25cd791bb78f76833896e4778f668861df12>= sumac, < ulmo

Weakness: CWE-79 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N

References

https://github.com/openedx/openedx-platform/security/advisories/GHSA-4xv3-5j4x-q8g4 x_refsource_CONFIRM
https://github.com/openedx/openedx-platform/commit/cddc25cd791bb78f76833896e4778f668861df12 x_refsource_MISC