CVE-2026-27807Network attack vector

Authenticated denial of service via YAML alias expansion

Published Mar 6, 2026 · Updated Mar 6, 2026

Denial of service in MarkUs before 2.9.4 allows remote authenticated users to interrupt the service via a crafted YAML upload. The upload path parses attacker-controlled YAML with aliases enabled, allowing a compact alias graph to expand exponentially and consume CPU and RAM. Course-instructor privileges are required, and successful exploitation makes the MarkUs service unavailable without affecting confidentiality or integrity.

CVSS severity4.9
Medium
EPSS probability0.28%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Denial of service in MarkUs before 2.9.4 allows remote authenticated users to interrupt the service via a crafted YAML upload. The upload path parses attacker-controlled YAML with aliases enabled, allowing a compact alias graph to expand exponentially and consume CPU and RAM. Course-instructor privileges are required, and successful exploitation makes the MarkUs service unavailable without affecting confidentiality or integrity.

The record

CVE
CVE-2026-27807
Published
Mar 6, 2026
Updated
Mar 6, 2026
Vendor
MarkUs
Product
MarkUs
Classifications
CWE-776, T1499.003
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 6, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 6, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2.9.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

MarkUs · MarkUsversion=< 2.9.4

Published CVSS scores

4.9GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-776Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')
T1499.003Application Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo