CVE-2021-20104Public exploitNetwork attack vector

Unauthenticated code execution via incomplete extension blacklist

Published Jun 29, 2021 · Updated Aug 3, 2024

Unrestricted file upload in MachForm before 16 allows remote attackers to execute PHP code through a crafted form attachment. The upload.php extension blacklist omits executable suffixes such as .pht, .php7, and .phps, so Apache can interpret an accepted attachment as PHP. Exploitation requires an active form plus discovery of its form ID and the randomized uploaded filename; successful code runs as the MachForm process owner.

CVSS severity8.1
High
EPSS probability2.15%
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 MachForm before 16 allows remote attackers to execute PHP code through a crafted form attachment. The upload.php extension blacklist omits executable suffixes such as .pht, .php7, and .phps, so Apache can interpret an accepted attachment as PHP. Exploitation requires an active form plus discovery of its form ID and the randomized uploaded filename; successful code runs as the MachForm process owner.

The record

CVE
CVE-2021-20104
Published
Jun 29, 2021
Updated
Aug 3, 2024
Vendor
Laymance Technologies LLC
Product
MachForm
Classifications
CWE-434, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 29, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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?

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

  1. Affected versionversion=All versions prior to version 16

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Laymance Technologies LLC · MachFormversion=All versions prior to version 16

Published CVSS scores

8.1NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P

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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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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