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MybbApplication

CVE-2011-10018

CRITICAL · 9.8 CVSS v3.1 Published 2025-08-13
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
Public exploit 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
myBB version 1.6.4 was distributed with an unauthorized backdoor embedded in the source code. The backdoor allowed remote attackers to execute arbitrary PHP code by injecting payloads into a specially crafted collapsed cookie. This vulnerability was introduced during packaging and was not part of the intended application logic. Exploitation requires no authentication and results in full compromise of the web server under the context of the web application.

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

myBB 1.6.4 contained an unauthorized backdoor embedded in the source code during the packaging process. The backdoor allows remote arbitrary PHP code execution through a specially crafted 'collapsed' cookie, requiring no authentication and resulting in full web server compromise.

MitigationImmediately decommission any myBB 1.6.4 installations and perform a clean reinstall from verified official sources; conduct forensic analysis to determine if the backdoor was exploited and assess for lateral movement or persistence mechanisms.

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
MybbApplication
Affected:= 1.6.4

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
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. Identify installed MyBB version
    Locate the version file - typically at /inc/databases.php or check the MyBB admin dashboard under 'Help' > 'System Details'. Also check /VERSION file in the root directory if it exists.
    Affected if The installed version is exactly 1.6.4 (note the '=' in the affected range indicates an exact version match)
  2. Inspect collapsed cookie handling code
    Search the source code for the string 'collapsed' and examine how this cookie is processed. The backdoor evaluates the cookie value as PHP code using eval() or similar functions.
    Affected if The source code contains eval() or create_function() calls that process the 'collapsed' cookie value without sanitization
  3. Check for suspicious eval() calls in cookie handlers
    Review PHP files in the main directory (particularly those handling user input or cookies) for eval() statements that process cookie variables, especially around the collapsed functionality.
    Affected if Any eval() call processes cookie input directly, indicating the backdoor is present
  4. Compare source to official MyBB 1.6.4 release
    If you have access to a known-clean MyBB 1.6.4 installation from official sources, compare file hashes or source code against the installed version, focusing on files that handle cookie processing.
    Affected if Files differ from the official release, particularly in cookie/collapsed handling routines

You are affected if you are running exactly MyBB 1.6.4 AND the source code contains eval() or similar code execution functions processing the 'collapsed' cookie parameter.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Immediately decommission any myBB 1.6.4 installations and perform a clean reinstall from verified official sources; conduct forensic analysis to determine if the backdoor was exploited and assess for lateral movement or persistence mechanisms.

Recommended fix High confidence

MyBB 1.6.5 or later

  1. 1. Back up your existing MyBB installation and database before proceeding with any upgrade.
  2. 2. Download MyBB 1.6.5 or a later stable version from the official MyBB website (mybb.com) or their official GitHub repository.
  3. 3. Extract the new MyBB files to a temporary location.
  4. 4. Upload the new files to your web server, overwriting the existing MyBB 1.6.4 installation.
  5. 5. Run the upgrade script by accessing your forum's URL (e.g., http://yourforum.com/install/upgrade.php) to complete the database migration.
  6. 6. Delete the install directory after successful upgrade for security.
  7. 7. Clear all cookies, especially any 'collapsed' cookies, to remove potentially malicious payloads.
  8. 8. Verify the upgrade was successful and test that the backdoor is no longer present.
Caveat Standard MyBB upgrade considerations apply - ensure plugin compatibility and backup before upgrading

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

Fix this in Mybb Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA3.0 h
19.0 hours of engineering $3,380
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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-2011-10018 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