CVE-2026-28405Network attack vector

Stored XSS via unsanitized submission preview

Published Mar 5, 2026 · Updated Mar 5, 2026

Stored XSS in MarkUs before 2.9.1 allows remote authenticated users to execute scripts when an instructor previews a submitted file. The html_content route reads a file from the submission repository and renders its contents without sanitization, including RMarkdown output and files reached through a crafted URL. Student privileges and instructor or grader interaction are required; the resulting script executes in the viewer's elevated application context.

CVSS severity8.0
High
EPSS probability0.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in MarkUs before 2.9.1 allows remote authenticated users to execute scripts when an instructor previews a submitted file. The html_content route reads a file from the submission repository and renders its contents without sanitization, including RMarkdown output and files reached through a crafted URL. Student privileges and instructor or grader interaction are required; the resulting script executes in the viewer's elevated application context.

The record

CVE
CVE-2026-28405
Published
Mar 5, 2026
Updated
Mar 5, 2026
Vendor
MarkUs Project
Product
MarkUs
Classifications
CWE-79, T1203
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 5, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.9.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

MarkUs Project · MarkUsversion=< 2.9.1

Published CVSS scores

8.0GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H
5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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