Kirby has Server-Side Template Injection (SSTI) via double template resolution in option rendering

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

7.6 · CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-34587: 0.33% estimated exploitation activity in the next 30 days; percentile 26.83 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

TL;DR This vulnerability affects all Kirby sites that use option fields (checkboxes, color, multiselect, select, radio, tags or toggles) with options from a query or API whose values may not be fully trusted. It also affects direct uses of the OptionsApi or OptionsQuery classes of Kirby's Options package from plugin or site code. The attack requires either an attacker in the group of authenticated Panel users or user interaction of another authenticated user. This vulnerability is of high severity for affected sites. Users' Kirby sites are not affected if they are not using any of the mentioned fields or the Options package, if all options are defined statically in the blueprints or if all dynamically gathered options are to be trusted. ---- Introduction Server-Side Template Injection vulnerabilities (SSTI) occur when user input is embedded in a template in an unsafe manner and results in remote code execution on the server. Injected user input is wrongly treated as a template…

Published by the source

23 Apr 2026, 21:24 UTC

Last modified by the source

5 May 2026, 15:43 UTC

Source last checked

26 Oct 2026, 14:39 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-jcjw-58rv-c452

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# Patch Next advisory brief: CVE-2026-34587

Advisory: Kirby has Server-Side Template Injection (SSTI) via double template resolution in option rendering
IDs: CVE-2026-34587, GHSA-jcjw-58rv-c452
Record: https://patchnext.com/advisories/cve-2026-34587 (revision 1, source checked 26 Oct 2026, 14:39 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: getkirby/cms 5.4.0, 4.9.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist getkirby/cms: affected < 4.9.0; >= 5.0.0, < 5.4.0; fixed in 4.9.0, 5.4.0

## Suggested inspection (read-only)
- Packagist getkirby/cms: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on getkirby/cms.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-jcjw-58rv-c452 (GitHub-reviewed advisory GHSA-jcjw-58rv-c452 lists affected ranges: Packagist getkirby/cms >=0 =5.0.0 <5.4.0)

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