⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● Critical · CVSS 10

How to Fix CVE-2026-33897: Server-Side Template Injection in incus

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

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityCVSS 10 - Critical
Actively exploited?Not currently listed in CISA KEV
Affected< 6.23.0
Fixed inSee vendor advisory
Type (CWE)CWE-1336: Improper Neutralization of Special Elements Used in a Template Engine

What is CVE-2026-33897?

CVE-2026-33897 is a server-side template injection flaw in incus. User input is rendered as part of a template expression, which the engine then evaluates, giving the attacker code execution. Vendor description: Incus is a system container and virtual machine manager. Prior to version 6.23.0, instance template files can be used to cause arbitrary read or writes as root on the host server.

Why this CVE matters

Server-side template injection is one of the cleanest paths from web request to code execution. The vulnerable parameter is usually attacker-controlled by design, which means proof-of-concept payloads are short and reliable.

For deployments of incus 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 incus'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-2026-33897

  1. Read the vendor advisory in full: https://github.com/lxc/incus/security/advisories/GHSA-83xr-5xxr-mh92
  2. Upgrade incus 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).

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Patch via your OS package manager

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

prerequisites): https://github.com/lxc/incus/security/advisories/GHSA-83xr-5xxr-mh92


# Vendor advisory: https://github.com/lxc/incus/security/advisories/GHSA-83xr-5xxr-mh92
# Debian / Ubuntu: pull the patched build of incus from your distro repository.
sudo apt update
sudo apt install --only-upgrade incus

# RHEL / Rocky / AlmaLinux / Fedora
sudo dnf upgrade incus

# openSUSE
sudo zypper update incus

# Verify the running version matches the fixed-in version (<patched-version>).
incus --version || dpkg -s incus | grep -i version || rpm -q incus


# 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://github.com/lxc/incus/security/advisories/GHSA-83xr-5xxr-mh92
# 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

Block the affected endpoint or input from untrusted users. There is no configuration-only mitigation; patch is required.

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 unexpected administrator accounts in incus, scheduled tasks or cron jobs you did not create, new files in web-accessible directories, and outbound connections to addresses not in your baseline. Suspicious requests to the vulnerable endpoint immediately followed by successful 200-class responses with unusually large bodies are a strong indicator of exploitation.

Frequently asked questions

Is CVE-2026-33897 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-2026-33897?

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 incus 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.*