Login Request a demo
Medium severity · published May 11, 2026
CVE-2026-42857
Open edX Platform: Stored CSS Injection in Email Notifications via Incomplete HTML Sanitization
5.4
CVSS
0.2%
EPSS
No
On KEV
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 vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
Required
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 8% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
OP
openedx-platform · openedx
< cddc25cd791bb78f76833896e4778f668861df12; >= sumac, < ulmo · source: vendor
OP
Openedx · Openedx
before 2026-04-24 · source: NVD
Affected product
OP
openedx-platform
openedx
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-42857
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-42857
Patch
https://github.com/openedx/openedx-platform/commit/cddc25cd791bb78f76833896e4778f668861df12
Exploit
https://github.com/openedx/openedx-platform/security/advisories/GHSA-4xv3-5j4x-q8g4
More from openedx-platform
9.9
CVE-2026-42858
Open edX Platform: Server-Side Request Forgery (SSRF) in SAML Provider Data Sync Endpoint
7.6
CVE-2026-53635
Open edX Platform: Insufficient Permission on set_course_mode_price()
6.8
CVE-2026-55421
Open edX Platform: SSRF in Studio Video Download Endpoint
6.1
CVE-2026-85271
Open edX Platform: Stored CSS Injection in Email Digest Notifications via Unsanitized Thread Title (incomplete patch of CVE-2026-42857)
6.1
CVE-2026-35404
Open edX Platform has an Open Redirect in Survey Views via Unvalidated redirect_url Parameter