CVE-2026-28405: MarkUsProject Markus · Cross-site Scripting
Affects MarkUsProject MarkusSource CVE Database V5
Not known to be exploited · CVSS 8.0 High : upgrade to 2.9.1 soon.
Data as of 30 Oct 2026, 11:52 UTC
- 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:HExploitation evidence
Disclosed: evidence found.
CVE published 5 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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
| Product | Affected | Fixed in |
|---|---|---|
| MarkUsProjectMarkus | Affected
| Fixed in
|
GitHubmarkusproject/Markuspkg:github/markusproject/MarkusOther threats | Affected
| Fixed in
|
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.