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Umbraco CmsApplication · Umbraco

CVE-2023-49278

MEDIUM · 5.3 CVSS v3.1 Published 2023-12-12
Fix available
A fix is available. Upgrade to 8.18.10 / 10.8.1 or later.
See remediation →
62/100
Remediation priority · Elevated
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
Umbraco is an ASP.NET content management system (CMS). Starting in version 8.0.0 and prior to versions 8.18.10, 10.8.1, and 12.3.4, a brute force exploit can be used to collect valid usernames. Versions 8.18.10, 10.8.1, and 12.3.4 contain a patch for this issue.

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

A brute force exploit in Umbraco CMS allows unauthenticated attackers to enumerate valid usernames by observing differences in system responses. The vulnerability affects versions 8.0.0 through versions prior to 8.18.10, 10.8.1, and 12.3.4. Successful exploitation provides usernames that could facilitate password spraying or credential stuffing attacks.

MitigationUpgrade Umbraco to version 8.18.10, 10.8.1, or 12.3.4 which contain the patch preventing username enumeration. Consider implementing rate limiting or account lockout policies as additional defense-in-depth measures.

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
Umbraco CmsApplication
Affected:>= 8.0.0, < 8.18.10>= 10.0.0, < 10.8.1>= 12.0.0, < 12.3.4

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
Low
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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. Identify the installed Umbraco version
    Check the Umbraco.dll file version in the /bin folder, or look for the Version setting in the web.config file under configuration/umbraco/configuration, or access the About page in the Umbraco backoffice if you have admin access
    Affected if The installed version falls within 8.0.0 to before 8.18.10, 10.0.0 to before 10.8.1, or 12.0.0 to before 12.3.4
  2. Confirm the login page is accessible
    Navigate to the default login endpoint (typically /umbraco/login or /backoffice/umbraco/login) on your website and verify the page loads
    Affected if The login page is publicly accessible without authentication (default configuration)
  3. Verify the password reset functionality is exposed
    Access the forgot password or password reset endpoint (typically /umbraco/forgotpassword or /backoffice/ForgotPassword) and confirm it loads
    Affected if The password reset functionality is publicly accessible (default configuration)
  4. Test for username enumeration response differences
    Submit two password reset requests: one with a known-valid username (such as your admin account) and another with a random invalid username. Compare the HTTP status codes and response messages
    Affected if The system returns different responses (different messages, different timing, or different HTTP status codes) for valid versus invalid usernames

You are affected if your Umbraco version is below 8.18.10 (for v8), below 10.8.1 (for v10), or below 12.3.4 (for v12) AND the login or password reset page is publicly accessible.

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 8.18.10 / 10.8.1 / 12.3.4 or later
Fixed in 8.18.1010.8.112.3.4
Interim mitigation

Upgrade Umbraco to version 8.18.10, 10.8.1, or 12.3.4 which contain the patch preventing username enumeration. Consider implementing rate limiting or account lockout policies as additional defense-in-depth measures.

Recommended fix High confidence

Umbraco CMS 8.18.10, 10.8.1, or 12.3.4 (depending on your current major version)

  1. 1. Back up your Umbraco database and all site files before proceeding with any upgrade.
  2. 2. Review the official Umbraco upgrade documentation for your current version path (8.x, 10.x, or 12.x).
  3. 3. Test the upgrade in a non-production/staging environment first to verify compatibility.
  4. 4. Upgrade to Umbraco CMS version 8.18.10 (if on v8), 10.8.1 (if on v10), or 12.3.4 (if on v12) following standard upgrade procedures.
  5. 5. After upgrade, verify that valid usernames can no longer be enumerated through the brute force exploit vector.
  6. 6. Deploy the upgraded version to production once testing is complete.
Caveat Consult Umbraco upgrade documentation for version-specific breaking changes; minor version upgrades typically have lower risk but test thoroughly

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

Fix this in Umbraco Cms Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing5.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,790
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,464.

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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-2023-49278 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