CVE-2026-21631: Lack of output escaping leads to a XSS vector in the multilingual associations component.

Routine

MEDIUM 5.4UPGRADE

CVE-2026-21631 is a medium-severity flaw (CVSS 5.4) affecting joomla\!. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Lack of output escaping leads to a XSS vector in the multilingual associations component.

Why this priority

Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	5.4 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	Required
EPSS exploit chance	0.2% (top 88%)
CISA exploited list	No
Weakness	CWE-79
Published	2026-04-01
Last modified	2026-10-26

Publisher (CNA): Joomla! Project · Vendor: joomla

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-01 10:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

joomla joomla\! UPGRADE

Affected: >= 3.0.0 and < 5.4.4 · >= 6.0.0 and < 6.0.4

Fixed in: 5.4.4, 6.0.4

Safe to downgrade to: a release before 3.0.0

1. Check installed version

apt-cache policy joomla || rpm -q joomla || joomla --version

2. UPGRADE to 5.4.4 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade joomla

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade joomla

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 3.0.0 (Debian / Ubuntu)

apt-cache madison joomla sudo apt install joomla=<VERSION_BEFORE_3.0.0> sudo apt-mark hold joomla

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list joomla sudo dnf downgrade joomla-<VERSION_BEFORE_3.0.0> sudo dnf versionlock add joomla

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-21631?

joomla\!: upgrade to 5.4.4, 6.0.4. Exact commands for each OS are on this page.

Is CVE-2026-21631 being exploited?

CVE-2026-21631 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-21631 affect?

CVE-2026-21631 affects joomla\!. Severity is medium (CVSS 5.4). Lack of output escaping leads to a XSS vector in the multilingual associations component.

How urgent is CVE-2026-21631?

Priority 27/100. Public exploit reference

Software pages

Joomla vulnerabilities

Related CVEs

CVE-2026-23899 HIGH 8.8 UPGRADE An improper access check allows unauthorized access to webservice endpoints.
CVE-2026-21630 HIGH 8.8 UPGRADE Improperly built order clauses lead to a SQL injection vulnerability in the articles webservice endpoint.
CVE-2026-21629 HIGH 7.3 UPGRADE The ajax component was excluded from the default logged-in-user check in the administrative area
CVE-2026-23898 HIGH 7.2 UPGRADE Lack of input validation leads to an arbitrary file deletion vulnerability in the autoupdate server mechanism.
CVE-2026-21632 MEDIUM 5.4 UPGRADE Lack of output escaping for article titles leads to XSS vectors in various locations.

References

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