⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● Medium · CVSS 4.9

How to Fix CVE-2026-37978: Insecure Direct Object Reference in Red Hat build of Keycloak 26.4

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

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityCVSS 4.9 - Medium
Actively exploited?Not currently listed in CISA KEV
AffectedRed Hat build of Keycloak 26.4 - see advisory for affected version ranges
Fixed in26.4.12-1, 26.4-17, 26.4-17
Type (CWE)CWE-639: Authorization Bypass Through User-Controlled Key

What is CVE-2026-37978?

CVE-2026-37978 is an insecure direct object reference (IDOR) in Red Hat build of Keycloak 26.4. The product uses a user-supplied identifier to fetch or modify a record without checking that the caller is allowed to touch that specific object, exposing or altering other users' data. Vendor description: A flaw was found in Keycloak. A low-privilege administrator with the 'view-clients' role can exploit this by invoking the 'evaluate-scopes' Admin API endpoints with an arbitrary user ID (userId) parameter.

Why this CVE matters

IDOR flaws bypass the application's intended tenant isolation. In multi-user products this typically means one customer can read or modify another customer's data with nothing more than a sequential identifier.

For deployments of Red Hat build of Keycloak 26.4 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?

Check your installed Red Hat build of Keycloak 26.4 version against the affected ranges in the vendor advisory linked below. If you cannot determine the version, treat the system as potentially affected and apply the patched build.

Open Red Hat build of Keycloak 26.4'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-2026-37978

  1. Read the vendor advisory in full: https://access.redhat.com/errata/RHSA-2026:19596
  2. Upgrade Red Hat build of Keycloak 26.4 to 26.4.12-1, 26.4-17, 26.4-17 or a later version 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).

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Patch via your OS package manager

Vendor advisory (always check this first for exact fixed version and any

prerequisites): https://access.redhat.com/errata/RHSA-2026:19597


# Vendor advisory: https://access.redhat.com/errata/RHSA-2026:19596
# Debian / Ubuntu: pull the patched build of red-hat-build-of-keycloak-26.4 from your distro repository.
sudo apt update
sudo apt install --only-upgrade red-hat-build-of-keycloak-26.4

# RHEL / Rocky / AlmaLinux / Fedora
sudo dnf upgrade red-hat-build-of-keycloak-26.4

# openSUSE
sudo zypper update red-hat-build-of-keycloak-26.4

# Verify the running version matches the fixed-in version (<patched-version>).
red-hat-build-of-keycloak-26.4 --version || dpkg -s red-hat-build-of-keycloak-26.4 | grep -i version || rpm -q red-hat-build-of-keycloak-26.4


# Windows: pull the latest cumulative updates that include this CVE's fix.
Install-Module PSWindowsUpdate -Force -SkipPublisherCheck
Import-Module PSWindowsUpdate
Get-WindowsUpdate -AcceptAll -Install -AutoReboot

# If a specific KB is referenced in the advisory, install it directly.
# Get-WindowsUpdate -KBArticleID KBxxxxxxx -AcceptAll -Install -AutoReboot

Verify the fix landed


# Vendor advisory: https://access.redhat.com/errata/RHSA-2026:19596
# 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 -u <service> --since "10 minutes ago"
dmesg --since "10 minutes ago"

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If you cannot patch immediately

Front the vulnerable endpoint with an authorization rule at a reverse proxy or API gateway that validates the caller's right to access the requested object. The patch is the only complete fix.

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-2026-37978 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-2026-37978?

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 Red Hat build of Keycloak 26.4 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.*