⚠ 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-2026-24733: Input Validation Flaw in Apache Tomcat

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
Affected11.0.0-M1 <= 11.0.14, 10.1.0-M1 <= 10.1.49, 9.0.0.M1 <= 9.0.112, 0 <= 8.5.100
Fixed inSee vendor advisory
Type (CWE)CWE-20: Improper Input Validation

What is CVE-2026-24733?

CVE-2026-24733 is an improper input validation flaw in Apache Tomcat. The product fails to verify the format, range, or origin of attacker-controlled input, and downstream code paths then act on values they should have rejected. Vendor description: Improper Input Validation vulnerability in Apache Tomcat. Tomcat did not limit HTTP/0.9 requests to the GET method.

Why this CVE matters

Input validation gaps in a management or API endpoint are usually a sign that other defensive layers were trusted to catch malformed input. When they do not, the impact ranges from data corruption to full code execution depending on what the unvalidated input controls.

For deployments of Apache Tomcat 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.

Run the project-specific version command (for example httpd -v, tomcat version, or check pom.xml / package metadata) and compare against the advisory.

How to fix CVE-2026-24733

  1. Read the vendor advisory in full: https://lists.apache.org/thread/6xk3t65qpn1myp618krtfotbjn1qt90f
  2. Upgrade Apache Tomcat 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).

Patch via the OS package manager


# Target fixed version: see advisory (https://lists.apache.org/thread/6xk3t65qpn1myp618krtfotbjn1qt90f)
# Source advisory: https://lists.apache.org/thread/6xk3t65qpn1myp618krtfotbjn1qt90f

# Debian / Ubuntu.
sudo apt update
sudo apt install --only-upgrade apache2
dpkg -s apache2 | grep -i version

# RHEL / Rocky / AlmaLinux / Fedora.
sudo dnf upgrade --refresh apache2 -y
rpm -q apache2

# openSUSE.
sudo zypper refresh
sudo zypper update apache2

# Restart any service backed by this package, then confirm the running version.
sudo systemctl restart apache2 2>/dev/null || true


# Vendor advisory: https://lists.apache.org/thread/6xk3t65qpn1myp618krtfotbjn1qt90f
# Container image refresh.
docker pull <your-registry>/apache2:<patched-tag>
docker stop <your-app> && docker rm <your-app>
docker run -d --name <your-app> <your-registry>/apache2:<patched-tag>


# Windows side of the fleet - install equivalent vendor update.
Install-Module PSWindowsUpdate -Force -SkipPublisherCheck -Confirm:$false
Import-Module PSWindowsUpdate
Get-WindowsUpdate -AcceptAll -Install -AutoReboot

Verify the fix landed


# 1. Confirm the running version matches the fixed-in version listed 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 --since "10 minutes ago" | tail -50
dmesg --since "10 minutes ago" 2>/dev/null | tail -50

If you cannot patch immediately

No official workaround exists beyond restricting network exposure to the affected component. Apply the vendor patch as the primary remediation.

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-2026-24733 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-2026-24733?

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 Apache Tomcat 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.*