⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● Not verified

How to Fix CVE-2026-5090: Cross-Site Scripting in Template::Plugin::HTML

Other vulnerabilities in the same area that are worth patching alongside this one:

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityNot verified - see advisory
Actively exploited?Not currently listed in CISA KEV
Affected0 <= 3.102
Fixed inSee vendor advisory
Type (CWE)CWE-79: Improper Neutralization of Input During Web Page Generation

What is CVE-2026-5090?

CVE-2026-5090 is a cross-site scripting (XSS) flaw in Template::Plugin::HTML. The product reflects or stores attacker-controlled input without proper escaping, so a crafted payload runs as JavaScript in the browser of any user who views the affected page. Impact ranges from session theft to full account takeover when an administrator is targeted. Vendor description: Template::Plugin::HTML versions through 3.102 for Perl allows HTML and JavaScript to be injected. The html_filter function did not escape single quotes.

Why this CVE matters

Stored XSS in a content-management product or admin console is a direct route to administrator takeover. Once a payload lands on a page an admin will view, the attacker inherits the same session privileges as the administrator.

For deployments of Template::Plugin::HTML that have been exposed to the public internet during the disclosure window, the operating assumption should be that scanning has already happened. Even where exploitation has not been publicly observed, scanning for the vulnerable fingerprint is cheap and routine. Patching closes the door; log review and credential rotation close out the rest of the response.

Am I affected?

You are affected if your installation matches any of these version ranges:

Check your installed version against the list above. If you cannot determine the version, treat the system as affected and follow the upgrade path below.

Open Template::Plugin::HTML's About dialog or run the vendor-documented version-check command. Compare the result against the affected ranges in the advisory.

How to fix CVE-2026-5090

  1. Read the vendor advisory in full: https://github.com/abw/Template2/issues/327
  2. Upgrade Template::Plugin::HTML to the patched build listed in the vendor advisory.
  3. Back up the configuration (and database, where applicable) before upgrading.
  4. Apply the patch in a maintenance window. For HA pairs, upgrade the standby node first, fail over, then upgrade the former primary.
  5. Restart the affected service so the patched binary loads, then verify the new version (see verification section).

Open-source library upgrade

The vendor advisory (https://github.com/abw/Template2/pull/337/changes/11c78a7a771d4af505efeb754a0b8775689c2eae) names the patched release as the build named in the vendor advisory (https://github.com/abw/Template2/pull/337/changes/11c78a7a771d4af505efeb754a0b8775689c2eae). Pull the

fixed version through whichever ecosystem actually ships template--plugin--html.


# Vendor advisory: https://github.com/abw/Template2/issues/327
# npm / pnpm / yarn
npm install template--plugin--html@latest
npm ls template--plugin--html

# Or pin to the patched version named in the advisory
npm install template--plugin--html@<patched-version>

# pip / Poetry
pip install --upgrade "template--plugin--html"
pip show template--plugin--html | grep -i version
poetry add "template--plugin--html@^<patched-version>"

# Go modules
go get example.com/template--plugin--html@<patched-version>
go mod tidy

# Rust crates
cargo update -p template--plugin--html

# Composer
composer require vendor/template--plugin--html:^<patched-version>


# Vendor advisory: https://github.com/abw/Template2/issues/327
# Container image: rebuild against the patched base and roll the deployment.
docker pull <your-registry>/template--plugin--html:<patched-tag>
docker stop <app> && docker rm <app>
docker run -d --name <app> <your-registry>/template--plugin--html:<patched-tag>

# Kubernetes
kubectl set image deployment/<deployment-name> <container>=<your-registry>/template--plugin--html:<patched-tag>
kubectl rollout status deployment/<deployment-name>

Linux package upgrade

The vendor advisory (https://github.com/abw/Template2/pull/337/changes/11c78a7a771d4af505efeb754a0b8775689c2eae) names the patched build as the build named in the vendor advisory (https://github.com/abw/Template2/pull/337/changes/11c78a7a771d4af505efeb754a0b8775689c2eae).


# Ubuntu / Debian
sudo apt-get update
sudo apt-get install --only-upgrade openjdk-17-jdk
dpkg -s openjdk-17-jdk | grep -i version

# RHEL / Rocky / AlmaLinux / Fedora
sudo dnf upgrade --refresh openjdk-17-jdk -y
rpm -q openjdk-17-jdk

# openSUSE
sudo zypper refresh && sudo zypper update openjdk-17-jdk

# Restart the service that loads the patched binary
sudo systemctl restart openjdk-17-jdk 2>/dev/null || true
sudo systemctl status openjdk-17-jdk --no-pager 2>/dev/null || true


# Vendor advisory: https://github.com/abw/Template2/issues/327
# Container deployments: rebuild with the patched package layer, then roll the workload.
docker pull <your-registry>/openjdk-17-jdk:<patched-tag>
docker stop <app> && docker rm <app>
docker run -d --name <app> <your-registry>/openjdk-17-jdk:<patched-tag>

# Kubernetes
kubectl set image deployment/<deployment-name> openjdk-17-jdk=<your-registry>/openjdk-17-jdk:<patched-tag>
kubectl rollout status deployment/<deployment-name>

Verify the fix landed


# Vendor advisory: https://github.com/abw/Template2/issues/327
# 1. Compare the running version against the fixed build named above.
#    (Replace the version probe with the platform-specific command from the block above.)

# 2. Re-scan with your vulnerability scanner (Nessus, Qualys, Tenable, OpenVAS).
#    The scanner should no longer flag this CVE on the patched target.

# 3. Inspect recent service / kernel logs for crash loops or rollback events.
journalctl -u <service> --since "10 minutes ago"
dmesg --since "10 minutes ago"

If you cannot patch immediately

Disable or restrict access to the affected page or feature for untrusted users until the patch is applied. Add a Content-Security-Policy header that disallows inline scripts and limits script sources to your own domain; this reduces the impact of stored XSS but does not remove the underlying flaw.

How to verify the fix worked

If your installation was internet-reachable during the disclosure window, treat log review as part of the remediation rather than an optional follow-up. Look for log entries that do not match your normal request patterns, especially repeated requests to the same uncommon endpoint, and any administrative changes you cannot tie back to a known operator.

Frequently asked questions

Is CVE-2026-5090 being exploited in the wild?

Public exploitation has not been confirmed by CISA at the time of writing. Treat the patch as time-sensitive anyway; reports often lag actual abuse.

Will a WAF or IDS rule fully mitigate CVE-2026-5090?

No. Network-layer filters can reduce noise and slow opportunistic scanners, but they will not stop a determined attacker. The vendor patch is the only durable fix.

How long should I plan for the upgrade?

Typical vendor-documented upgrade windows for Template::Plugin::HTML run from a few minutes to under an hour depending on cluster size. Test in a staging environment first and follow the vendor's documented HA upgrade order.

References

*This guide was assembled from the official vendor advisory, the NVD record, and the CISA KEV catalog entry on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*