CVE-2021-39392Network attack vector

Unauthenticated code execution via shared machineKey

Published Sep 15, 2021 · Updated Aug 4, 2024

Deserialization in MyLittleBackup 1.7 and earlier allows remote attackers to execute arbitrary code through its management tool. The web.config file reuses one hardcoded machineKey across customer installations, letting attackers forge a valid serialized ASP.NET payload. Network access to the management endpoint is sufficient; no authentication or user interaction is required, and successful exploitation runs attacker-supplied code.

CVSS severity9.8
Critical
EPSS probability2.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Deserialization in MyLittleBackup 1.7 and earlier allows remote attackers to execute arbitrary code through its management tool. The web.config file reuses one hardcoded machineKey across customer installations, letting attackers forge a valid serialized ASP.NET payload. Network access to the management endpoint is sufficient; no authentication or user interaction is required, and successful exploitation runs attacker-supplied code.

The record

CVE
CVE-2021-39392
Published
Sep 15, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-502, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 15, 2021CVE 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 National Vulnerability DatabaseAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8NIST National Vulnerability DatabaseCVSS: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.

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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 exploitUnconfirmed

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
T1190Exploit Public-Facing Application

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

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Your stack

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