Vulnerability · Published Mar 5, 2026 · Assigned by GitHub_M
CVE-2026-28405MarkUs: Stored XSS in Submission HTML Preview Enables Instructor-Context Actions
High 8.0
In plain English
A high-severity cross-site scripting in Markus from MarkUsProject. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 18% of all known vulnerabilities).
Severity (CVSS 3.1)8.0High
Exploit odds (30 days)0.3%top 82.2% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| MarkUsProject | Markus | < 2.9.1 |
Weakness: CWE-79 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H