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VulnerabilityPublished

CVE-2026-28405: MarkUsProject Markus · Cross-site Scripting

Affects MarkUsProject MarkusSource CVE Database V5

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Not known to be exploited · CVSS 8.0 High : upgrade to 2.9.1 soon.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score
8.0High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 14% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 2.9.1
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 5 Mar 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade Markus and markusproject/Markus to 2.9.1.

Affected software

ProductAffectedFixed in
MarkUsProjectMarkusAffected
  • <2.9.1
Fixed in
  • 2.9.1
GitHubmarkusproject/Markuspkg:github/markusproject/MarkusOther threatsAffected
  • <2.9.1
Fixed in
  • 2.9.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

To mitigate CVE-2026-28405, organizations should immediately upgrade Markus to version 2.9.1 or later where the vulnerability is patched. In addition to patching, implement strict input validation and sanitization on all user-submitted content, especially HTML or rich text inputs. Employ output encoding techniques to neutralize any potentially malicious scripts before rendering content in browsers. Restrict file types and content formats allowed for submission to reduce risk. Use Content Security Policy (CSP) headers to limit the execution of unauthorized scripts. Monitor logs for suspicious activity related to assignment submissions and user interactions. Educate users about the risks of clicking on untrusted content even within authenticated sessions. Conduct regular security assessments and code reviews focusing on input handling and output rendering. Consider deploying web application firewalls (WAFs) with rules targeting XSS attack patterns as an additional layer of defense.

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.

References

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