CVE-2026-27807 PUBLISHED

MarkUs: YAML alias (‘billion laughs’) DoS in config upload

Assigner: GitHub_M
Reserved: 24.02.2026 Published: 06.03.2026 Updated: 06.03.2026

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.

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
CVSS Score: 4.9

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
Privileges Required	High	Integrity Impact	None
User Interaction	None	Availability Impact	High

CVSS 3.1

Product Status

Vendor	MarkUsProject
Product	Markus
Versions	Version < 2.9.4 is affected

References

https://github.com/MarkUsProject/Markus/security/advisories/GHSA-m9rx-85mx-q9h6
https://github.com/MarkUsProject/Markus/releases/tag/v2.9.4

Problem Types

CWE-776: Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion') CWE