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MoodleCMS

CVE-2021-40693

MEDIUM · 6.5 CVSS v3.1 Published 2022-09-29
Fix available
A fix is available. Upgrade to 3.9.10 / 3.10.7 or later.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable 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
An authentication bypass risk was identified in the external database authentication functionality, due to a type juggling vulnerability.

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 · moderate confidence

This is a type juggling vulnerability in external database authentication where loose type comparisons (==) allow attackers to bypass authentication by manipulating data types during the authentication process. The vulnerability stems from improper handling of comparison operations, likely when validating credentials against an external database.

MitigationReplace all loose comparisons (==) with strict comparisons (===) in authentication logic, implement strict type validation on all user inputs, and ensure proper type handling throughout the credential verification process.

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
MoodleCMS
Affected:< 3.9.10>= 3.10.0, < 3.10.7>= 3.11.0, < 3.11.3

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
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

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

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. Determine Moodle version
    Log into the Moodle admin dashboard and navigate to Site administration > Server > Environment, or check the version.php file in the Moodle root directory for the $version variable
    Affected if The installed version falls within < 3.9.10, >= 3.10.0 and < 3.10.7, or >= 3.11.0 and < 3.11.3
  2. Confirm external database authentication plugin is enabled
    Navigate to Site administration > Plugins > Authentication > Manage authentication in the Moodle admin interface, and check if the 'External database' auth plugin is enabled
    Affected if External database authentication is enabled and the Moodle version is in the affected range
  3. Inspect authentication code for loose comparisons
    Examine the auth/db/auth.php file (or equivalent external database auth handler) and search for comparison operators using == instead of === in credential validation logic, particularly around password or username verification
    Affected if The authentication code contains loose comparisons (==) in the external database authentication logic

You are affected if your Moodle version is in the affected range AND you have the external database authentication method enabled AND your authentication code contains loose type comparisons that could be exploited via type juggling.

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 3.9.10 / 3.10.7 / 3.11.3 or later
Fixed in 3.9.103.10.73.11.3
Interim mitigation

Replace all loose comparisons (==) with strict comparisons (===) in authentication logic, implement strict type validation on all user inputs, and ensure proper type handling throughout the credential verification process.

Recommended fix High confidence

Moodle 3.9.10, 3.10.7, or 3.11.3 (depending on your current major version branch)

  1. 1. Backup the Moodle database and moodledata directory before proceeding
  2. 2. Download the fixed Moodle version (3.9.10, 3.10.7, or 3.11.3) from the official Moodle downloads page
  3. 3. Place the site into maintenance mode via Site administration > Server > Maintenance mode
  4. 4. Replace the existing Moodle code directory with the new version files
  5. 5. Run the Moodle upgrade via command line: php admin/cli/upgrade.php (or access via web browser)
  6. 6. After upgrade completes, clear all caches via Site administration > Development > Purge caches
  7. 7. Verify the external database authentication is functioning correctly with the new version
  8. 8. Disable maintenance mode
Caveat Standard Moodle upgrade considerations apply - review the Moodle release notes for any between-version changes that may affect custom code or plugins

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

Fix this in Moodle Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,088.

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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-2021-40693 in production — separate from our analysis above.

No notes yet

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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