CVE-2026-27807— MarkUs: YAML alias (‘billion laughs’) DoS in config upload
Quick assessment
Affected
MarkUsProject Markus
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
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 2.9.4之前版本存在安全漏洞，该漏洞源于允许课程讲师上传YAML文件创建或更新实体，且解析YAML文件时启用了别名。
Possible ATT&CK Techniques 1 AI
T1190 · Exploit Public-Facing Application
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I. Basic Information for CVE-2026-27807
Vulnerability Information
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Vulnerability Title
MarkUs: YAML alias (‘billion laughs’) DoS in config upload
Source: CVE Program / CVE List V5
Vulnerability Description
MarkUs is a web application for the submission and grading of student assignments. Prior to version 2.9.4, MarkUs allows course instructors to upload YAML files to create/update various entities (e.g., assignment settings). These YAML files are parsed with aliases enabled. This issue has been patched in version 2.9.4.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
DTD中递归实体索引的不恰当限制(XML实体扩展)
Source: CVE Program / CVE List V5
Vulnerability Title
MarkUs 安全漏洞
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 2.9.4之前版本存在安全漏洞，该漏洞源于允许课程讲师上传YAML文件创建或更新实体，且解析YAML文件时启用了别名。
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 | < 2.9.4 | - |
|
II. Public POCs for CVE-2026-27807
| # | POC Description | Source Link | Shenlong Link |
|---|
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Vendor Advisories for CVE-2026-27807 (1)
Vendor Pages for CVE-2026-27807 (1)
-
Release v2.9.4 · MarkUsProject/Markus · GitHub x_refsource_MISC
IV. Related Vulnerabilities
Same product: Markus
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CVE-2026-25962
MarkUs: Zip bomb in config upload enables DoS -
CVE-2026-28405
MarkUs: Stored XSS in Submission HTML Preview Enables Instru -
CVE-2026-25057
Zip Slip in MarkUs config upload allowing RCE -
CVE-2026-24900
MarkUs has a submission-view IDOR exposes all student submis -
CVE-2024-51743
Arbitrary File Write leading up to remote code execution (in
Same vendor: MarkUsProject
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CVE-2026-25962
MarkUs: Zip bomb in config upload enables DoS -
CVE-2026-28405
MarkUs: Stored XSS in Submission HTML Preview Enables Instru -
CVE-2026-25057
Zip Slip in MarkUs config upload allowing RCE -
CVE-2026-24900
MarkUs has a submission-view IDOR exposes all student submis -
CVE-2024-51743
Arbitrary File Write leading up to remote code execution (in
Same weakness: CWE-776
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V. Comments for CVE-2026-27807
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