CVE-2021-42654Public exploitNetwork attack vector

Unauthenticated code execution via disguised ASP.NET upload

Published May 24, 2022 · Updated Aug 4, 2024

Unrestricted file upload in SiteServer CMS before 5.1 allows remote attackers to execute arbitrary code through a crafted upload. The /api/stl/actions/upload/1 endpoint accepts ASP.NET code in a file named with the .aasspx extension while its declared MIME type and form name claim a PNG, then stores an executable .aspx file. No authentication or configuration change is required, although locating the timestamp-derived output name requires guessing before the uploaded web shell can run commands.

CVSS severity9.8
Critical
EPSS probability1.70%
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 SiteServer CMS before 5.1 allows remote attackers to execute arbitrary code through a crafted upload. The /api/stl/actions/upload/1 endpoint accepts ASP.NET code in a file named with the .aasspx extension while its declared MIME type and form name claim a PNG, then stores an executable .aspx file. No authentication or configuration change is required, although locating the timestamp-derived output name requires guessing before the uploaded web shell can run commands.

The record

CVE
CVE-2021-42654
Published
May 24, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-434, CAPEC-1, T1505.003, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 24, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record 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

7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-434Unrestricted Upload of File with Dangerous Type
CAPEC-1Accessing Functionality Not Properly Constrained by ACLs
T1505.003Web Shell
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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