CVE-2021-27280Public exploitNetwork attack vector

Unauthenticated command execution via malicious FreeMarker theme

Published May 8, 2023 · Updated Jan 29, 2025

OS command injection in mblog 3.5.0 allows remote attackers to execute arbitrary commands by uploading and selecting a crafted theme. ThemeController accepts an unauthenticated ZIP upload, and BlogUtils.uploadTheme extracts attacker-controlled FreeMarker files into the template path. The published proof of concept relies on a Shiro authorization bypass to reach the upload and activation endpoints; loading the home page then evaluates the malicious template with server-process privileges.

CVSS severity7.8
High
EPSS probability0.97%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

OS command injection in mblog 3.5.0 allows remote attackers to execute arbitrary commands by uploading and selecting a crafted theme. ThemeController accepts an unauthenticated ZIP upload, and BlogUtils.uploadTheme extracts attacker-controlled FreeMarker files into the template path. The published proof of concept relies on a Shiro authorization bypass to reach the upload and activation endpoints; loading the home page then evaluates the malicious template with server-process privileges.

The record

CVE
CVE-2021-27280
Published
May 8, 2023
Updated
Jan 29, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-434, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 8, 2023CVE publishedPublication date reported by the CVE source.
  2. Jan 29, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
7.8CISA-ADPCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-434Unrestricted Upload of File with Dangerous Type
T1190Exploit Public-Facing Application

Public exploit references

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

Technologies

Your stack

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Your stack

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