How severe is CVE-2026-42857?

CVE-2026-42857 has a CVSS 3.x base score of 4.6, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-42857 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (11th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-42857?

CVE-2026-42857 affects Openedx. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-42857?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-42857 have an EU (EUVD) identifier?

Yes. CVE-2026-42857 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29165.

When was CVE-2026-42857 published?

CVE-2026-42857 was published on 2026-05-11 and last updated on 2026-06-17.

CVE-2026-42857

CVE-2026-42857 is a medium-severity vulnerability in Openedx with a CVSS 3.x base score of 4.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 4.6)
EPSS exploit prediction: 0% (11th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-29165
Weakness: CWE-79
Affected product: Openedx
Published: 2026-05-11
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2026-42857?: 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.
How severe is CVE-2026-42857?: CVE-2026-42857 has a CVSS 3.x base score of 4.6, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-42857 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (11th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-42857?: CVE-2026-42857 affects Openedx. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-42857?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-42857 have an EU (EUVD) identifier?: Yes. CVE-2026-42857 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29165.
When was CVE-2026-42857 published?: CVE-2026-42857 was published on 2026-05-11 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:openedx:openedx:*:*:*:*:*:*:*:*

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