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CVE-2026-28405— MarkUs: Stored XSS in Submission HTML Preview Enables Instructor-Context Actions

Quick assessment

Affected
MarkUsProject Markus
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

MarkUs是MarkUs开源的一个 Ruby on Rails 和 React web 应用程序，用于提交和评分学生作业。 MarkUs 2.9.1之前版本存在跨站脚本漏洞，该漏洞源于读取和渲染学生提交的文件内容时未进行清理。

CVSS 8.0 · High EPSS 0.43% · P35
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I. Basic Information for CVE-2026-28405

Vulnerability Information
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Vulnerability Title
MarkUs: Stored XSS in Submission HTML Preview Enables Instructor-Context Actions
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5
Vulnerability Title
MarkUs 跨站脚本漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
MarkUs是MarkUs开源的一个 Ruby on Rails 和 React web 应用程序，用于提交和评分学生作业。 MarkUs 2.9.1之前版本存在跨站脚本漏洞，该漏洞源于读取和渲染学生提交的文件内容时未进行清理。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
MarkUsProject Markus < 2.9.1 -

II. Public POCs for CVE-2026-28405

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 8703 chars
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III. Intelligence Information for CVE-2026-28405

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Patches & Fixes for CVE-2026-28405 (1)

Vendor Advisories for CVE-2026-28405 (1)

IV. Related Vulnerabilities

Same product: Markus
Same vendor: MarkUsProject
Same weakness: CWE-79

V. Comments for CVE-2026-28405

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