Joomla\!Application · Joomla
CVE-2020-8421
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! before 3.9.15. Inadequate escaping of usernames allows XSS attacks in com_actionlogs.
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 confidenceCross-site scripting (XSS) vulnerability in Joomla! com_actionlogs component due to insufficient output encoding of usernames. Attackers can inject malicious scripts through user profile data that gets logged and displayed without proper escaping.
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
>= 3.9.0, < 3.9.14CVSS 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
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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 checksWork through these to decide whether this CVE applies to you.
-
Determine Joomla versionCheck the version.php file in the Joomla library directory (libraries/cms/version/version.php) or access the administrator backend and look at the 'About Joomla' pageAffected if The installed version is 3.9.0 through 3.9.13 (versions below 3.9.14)
-
Verify com_actionlogs component is presentCheck the database #__extensions table for the com_actionlogs component entry, or verify the directory /administrator/components/com_actionlogs/ existsAffected if The com_actionlogs component is installed on the system
-
Confirm Action Logs plugin is enabledCheck the #__extensions table for the 'plg_system_actionlogs' plugin entry with enabled=1, or view the Plugins page in Joomla administrator and look for 'System - Action Logs'Affected if The System - Action Logs plugin is enabled and running
-
Check if any users have logged activityQuery the #__action_logs table in the database to see if any action log records exist, or view the Action Logs component in the administrator backendAffected if There are action log entries present in the system showing user activity
-
Inspect username storage in action logsExamine records in the #__action_logs table, specifically the 'link' or 'extended_data' fields that may contain usernames, using a database queryAffected if Usernames from user profiles are being stored in action log records without visible encoding
A system is affected if it runs Joomla version 3.9.0 through 3.9.13 with the com_actionlogs component installed and the Action Logs plugin enabled, allowing stored XSS through unsanitized usernames in the action logs display.
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 data3.9.14
Upgrade Joomla! to version 3.9.15 or later, which implements proper escaping of usernames in the action logs component.
Fix this in Joomla\!
Scoped from the published advisory
- Consultation1.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-8421 — 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-2020-8421 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
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.
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
- No spam, self-promotion, credentials, or personal data