CVE-2026-28405 PUBLISHED

MarkUs: Stored XSS in Submission HTML Preview Enables Instructor-Context Actions

Assigner: GitHub_M
Reserved: 27.02.2026 Published: 05.03.2026 Updated: 06.03.2026

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.

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H
CVSS Score: 8

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	High
Privileges Required	Low	Integrity Impact	High
User Interaction	Required	Availability Impact	High

CVSS 3.1

Product Status

Vendor	MarkUsProject
Product	Markus
Versions	Version < 2.9.1 is affected

References

https://github.com/MarkUsProject/Markus/security/advisories/GHSA-p5pc-pxrj-3893
https://github.com/MarkUsProject/Markus/commit/55d74f2ddb72d2ec2f29aa2b4cb6b2da10755036
https://github.com/MarkUsProject/Markus/releases/tag/v2.9.1

Problem Types

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') CWE