Medium severity · published Mar 6, 2026
CVE-2026-27807
MarkUs: YAML alias (‘billion laughs’) DoS in config upload
4.9
CVSS
0.3%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
High
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 22% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Markus · MarkUsProject
< 2.9.4 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-27807
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-27807
Product
https://github.com/MarkUsProject/Markus/releases/tag/v2.9.4
Vendor Advisory
https://github.com/MarkUsProject/Markus/security/advisories/GHSA-m9rx-85mx-q9h6
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