CVE-2026-27807 json
MarkUs: YAML alias (‘billion laughs’) DoS in config upload
published 8mo ago modified 4mo ago also EUVD-2026-9968
- cvss
- 4.9
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.3%
- EPSS 0.3% chance of exploitation in 30 days, percentile 25%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
Is CVE-2026-27807 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 8mo ago
Exploit prediction
0.32% chance of exploitation in the next 30 days, higher than 25% of all scored CVEs (FIRST EPSS, 2026-11-09).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 4.9 | CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H |
Affected products
- MarkUsProject Markus
Classification
- Weakness
-
- CWE-776 Improper Restriction of Recursive Entity References in DTDs
References
-
github.com
/MarkUsProject/Markus/security/advisories/GHSA-m9rx-85mx-q9h6
vendor-advisory
-
github.com
/MarkUsProject/Markus/releases/tag/v2.9.4
product, release-notes
Sources
- CVE List CVE-2026-27807
- NVD CVE-2026-27807
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.
CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.