What is CVE-2026-28405?

CVE-2026-28405 is a high-severity vulnerability in Markusproject Markus, classified under Cross-site Scripting. CVSS score: 8.0/10. Published 2026-03-05.

How severe is CVE-2026-28405?

High severity. CVSS v3 base score is 8.0 out of 10.

XSS in Markusproject Markus

CVE-2026-28405

MarkUs is a web application for the submission and grading of student assignments. Prior to version 2.9.1, the courses/<:course_id>/assignments/<:assignment_id>/submissions/html_content route reads the contents of a student-submitted file and renders them without sanitization. This issue has been patched in version 2.9.1.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2026-03-05 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 8.0 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.004 (32.8th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 33rd percentile — 32.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.004 · change: +0.002

Affected products

Markusproject Markus — versions < 2.9.1

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

github.com/MarkUsProject/Markus/security/advisories/GHSA-p5pc-pxrj-3893 (Vendor Advisory)
github.com/MarkUsProject/Markus/commit/55d74f2ddb72d2ec2f29aa2b4cb6b2da10755036 (Patch)
github.com/MarkUsProject/Markus/releases/tag/v2.9.1 (Release Notes)

Frequently asked questions

What is CVE-2026-28405?: CVE-2026-28405 is a high-severity vulnerability in Markusproject Markus, classified under Cross-site Scripting. CVSS score: 8.0/10. Published 2026-03-05.
How severe is CVE-2026-28405?: High severity. CVSS v3 base score is 8.0 out of 10.