Joomla\!Application · Joomla
CVE-2021-26036
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 · uneditedAn issue was discovered in Joomla! 2.5.0 through 3.9.27. Missing validation of input could lead to a broken usergroups table.
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 confidenceJoomla! versions 2.5.0 through 3.9.27 contain a missing input validation vulnerability that allows malformed data to be written to the usergroups table, potentially corrupting or breaking the table structure and associated user access controls.
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
Joomla\!Application
>= 2.5.0, <= 3.9.27CVSS 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
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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 checksWork through these to decide whether this CVE applies to you.
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Check installed Joomla! versionAccess the Joomla! administrator panel and navigate to Help > About, or query the database table (typically #__options) for the 'version' entry. Alternatively, check the libraries/cms/version/version.php file if you have file system access.Affected if The installed version is 2.5.0, 3.9.27, or any version in between (2.5.0 <= version <= 3.9.27)
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Identify the database prefixExamine your Joomla! configuration.php file for the '$dbprefix' variable, which defines the database table prefix used for all Joomla! tables.Affected if A prefix is configured (this is required for the next check)
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Inspect the usergroups table structureQuery the database table (typically #__usergroups) using: DESCRIBE [prefix]_usergroups; or SELECT * FROM [prefix]_usergroups; Check for any unexpected columns, NULL values in required fields, or malformed parent_id references.Affected if The table contains unexpected NULL values in fields that should be NOT NULL, or parent_id values that reference non-existent group IDs, or duplicate group titles that should be unique
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Verify user access control integrityQuery the database to identify orphaned records: SELECT * FROM [prefix]_usergroups WHERE parent_id NOT IN (SELECT id FROM [prefix]_usergroups); Also check for duplicate lft/rgt values that should be unique in the nested set model.Affected if Orphaned records exist (parent_id references a non-existent group), or duplicate lft/rgt values are found in the usergroups table
A user is affected if they are running Joomla! versions 2.5.0 through 3.9.27 AND the #__usergroups table contains malformed or corrupted data due to the input validation vulnerability.
Generated from the published advisory. Verify against your own configuration.
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.
From vendor dataUpdate Joomla! to version 3.9.28 or later to obtain the patched version. Before updating, backup the database and verify compatibility of installed extensions with the new version.
Fix this in Joomla\!
Scoped from the published advisory
- Consultation2.0 h
- Implementation3.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,040.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-26036 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-26036 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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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.
- 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
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