dbcve.org
MylittlebackupApplication · Mylittletools

CVE-2021-39392

CRITICAL · 9.8 CVSS v3.1 Published 2021-09-15
Fix available
A fix is available. Upgrade to after 1.7 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
The management tool in MyLittleBackup up to and including 1.7 allows remote attackers to execute arbitrary code because machineKey is hardcoded (the same for all customers' installations) in web.config, and can be used to send serialized ASP code.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

MyLittleBackup up to v1.7 contains a hardcoded machineKey in web.config that is identical across all customer installations. This allows attackers to craft malicious serialized ASP payloads using the known encryption key, leading to remote code execution on the affected server.

MitigationReplace the hardcoded machineKey with a unique, cryptographically strong key pair (validationKey and decryptionKey) generated specifically for this installation. Ensure any existing serialized data is handled appropriately during the key rotation.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
MylittlebackupApplication
Affected:<= 1.7

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Confirm MyLittleBackup installation and version
    Locate the MyLittleBackup installation directory and check the version number of the software (often found in a README, version info file, or the web.config appSettings).
    Affected if The installed version is 1.7 or lower.
  2. Locate the web.config file
    Find the web.config file within the MyLittleBackup application directory or web root.
    Affected if The web.config file exists in the application directory.
  3. Inspect for machineKey element
    Open the web.config file and search for a <machineKey> element within the <system.web> section.
    Affected if A <machineKey> element is present in the web.config.
  4. Verify hardcoded key usage
    Examine the validationKey and decryptionKey attributes within the <machineKey> element. Check if these values appear static or identical to what would be found in default installations.
    Affected if The validationKey and decryptionKey values are hardcoded and not unique to this installation.

If MyLittleBackup version 1.7 or lower is installed and its web.config contains a hardcoded machineKey with static validationKey and decryptionKey values, the environment is affected by CVE-2021-39392.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to a release after 1.7
Interim mitigation

Replace the hardcoded machineKey with a unique, cryptographically strong key pair (validationKey and decryptionKey) generated specifically for this installation. Ensure any existing serialized data is handled appropriately during the key rotation.

Recommended fix Low confidence

Latest version newer than 1.7 (check www.mylittlebackup.com for exact release)

  1. 1. Navigate to the official MyLittleBackup website (www.mylittlebackup.com) to check for the latest version.
  2. 2. Download and install the latest version of MyLittleBackup that is newer than version 1.7.
  3. 3. After upgrading, verify that the web.config file now contains a unique, randomly generated machineKey for your installation.
  4. 4. If a unique machineKey is not automatically generated during upgrade, manually generate a new machineKey using ASP.NET tools or libraries and update the web.config file.
  5. 5. Test the application to ensure normal functionality after the upgrade and configuration change.
Caveat Minor - ensure application functions correctly after upgrade and new machineKey configuration

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Mylittlebackup Scoped from the published advisory
  • Consultation3.0 h
  • Implementation3.0 h
  • Testing6.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,400
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,840.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2021-39392 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-39392 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data