CVE-2026-27807 MarkUs: YAML alias (‘billion laughs’) DoS in config upload
Medium 4.9
Published
Updated
Check this codebase for CVE-2026-27807 and fix it if it is affected.
What it is: CVE-2026-27807 is a medium-severity vulnerability in MarkUsProject Markus, published on 6 Mar 2026.
Exploitation: There is no known exploitation of CVE-2026-27807 in the wild and no public exploit code.
Affected product: MarkUsProject Markus. No package-level version data is available, so check the vendor advisory linked from the reference page.
Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.
Reference: https://insights.sbomify.com/CVE-2026-27807/ (Markdown: https://insights.sbomify.com/CVE-2026-27807/index.md)
- Exploited in the wild
- Not known
- Fix
- None listed
What is CVE-2026-27807?
CVE-2026-27807 is a medium-severity vulnerability in MarkUsProject Markus, published on 6 Mar 2026.
Official 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.
Weakness: CWE-776
Which versions are affected by CVE-2026-27807?
It affects 1 product.
Products include Markusproject Markus.
How do I fix CVE-2026-27807?
No fix has been published for CVE-2026-27807 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-27807 being exploited?
There is no known exploitation of CVE-2026-27807 in the wild and no public exploit code.
Other vulnerabilities in MarkUsProject Markus
- CVE-2026-25057 Zip Slip in MarkUs config upload allowing RCE
- CVE-2026-28405 MarkUs: Stored XSS in Submission HTML Preview Enables Instructor-Context Actions
- CVE-2024-51499 MarkUs Arbitrary File Write leading up to remote code execution (student accounts)
- CVE-2024-51743 Arbitrary File Write leading up to remote code execution (instructor accounts)
- CVE-2026-25962 MarkUs: Zip bomb in config upload enables DoS
Sources
Also known as GHSA-m9rx-85mx-q9h6.