CVE-2021-28998Public exploitNetwork attack vector

Admin code execution via PHAR extension bypass

Published May 8, 2023 · Updated Jan 29, 2025

Unrestricted file upload in CMS Made Simple 2.2.15 and earlier allows remote authenticated users to execute code via a crafted PHAR file. The FilePicker upload handler rejects extensions only when they contain the string php, so a .phar payload passes validation and remains web-accessible. Administrative access to MicroTiny's CMSMS File Picker is required; requesting the uploaded PHAR executes its embedded PHP as a webshell.

CVSS severity7.2
High
EPSS probability1.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Unrestricted file upload in CMS Made Simple 2.2.15 and earlier allows remote authenticated users to execute code via a crafted PHAR file. The FilePicker upload handler rejects extensions only when they contain the string php, so a .phar payload passes validation and remains web-accessible. Administrative access to MicroTiny's CMSMS File Picker is required; requesting the uploaded PHAR executes its embedded PHP as a webshell.

The record

CVE
CVE-2021-28998
Published
May 8, 2023
Updated
Jan 29, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-434, T1505.003
Attack vector
network
Privileges
admin

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 privilegesadmin

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.2NIST NVDCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
7.2CISA-ADPCVSS:3.1/AV:N/AC:L/PR:H/UI:N/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
Privilegesadmin
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-434Unrestricted Upload of File with Dangerous Type
T1505.003Server Software Component: Web Shell

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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