CVE-2026-34587 — getkirby/cms
CVE-2026-34587 is a CWE-1336 vulnerability in getkirby/cms. A fix is available for getkirby/cms — see the affected versions and patch details below.
Kirby has Server-Side Template Injection (SSTI) via double template resolution in option rendering
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-34587.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
getkirby/cms🐘getkirby/cmsReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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 command instead of as a literal string of text. This allows attackers to query arbitrary information from the affected system or call arbitrary methods to perform actions.
In a Kirby site this can be used to access protected site information, alter site content or break site behavior.
Impact
Kirby provides field types (checkboxes, color, multiselect, select, radio, tags and toggles) that offer a fixed set of options from a configured list. This configured list can be statically defined in the blueprint or it can come from a Kirby query or (external) API source. Options coming from a query or API are treated as dynamic.
Static options can contain queries in the form {{ query }} or {< query >} that are then evaluated to a static value. Because the queries are defined in the blueprint, they can be trusted and cannot be controlled by attackers.
However, dynamic options can often not be trusted. This is why the "options from query" and "options from API" modes are intended to resolve the option values and text strings based on queries not defined within the data source but within the blueprint.
Unfortunately, the results of these trusted queries on untrusted source data are run through the query parser a second time in affected Kirby releases.
Because of the double-resolution of dynamic option values and text strings, attackers could place malicious query templates such as {{ users.first.password }} or {{ page.delete }} in the option sources such as page titles or external API data controlled by the attacker. These queries would then be executed when the field is loaded in the Panel. When the attacker directly accesses the respective Panel view, they could get access to information normally hidden from them. As the malicious query templates are loaded for all users, it could also lead to malicious write access when another user with a higher permission level accesses the manipulated Panel view.
Patches
The problem has been patched in Kirby 4.9.0 and Kirby 5.4.0. Please update to one of these or a later version to fix the vulnerability.
In all of the mentioned releases, Kirby has updated the Options logic to no longer double-resolve queries in option values coming from OptionsQuery or OptionsApi sources. Kirby now only resolves queries that are directly configured in the blueprints.
Credits
Kirby thanks to @offset for responsibly reporting the identified issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | getkirby/cms | all versions | 4.9.0composer require getkirby/cms:^4.9.0 |
| 🐘Packagist | getkirby/cms | ≥ 5.0.0&&< 5.4.0 | 5.4.0composer require getkirby/cms:^5.4.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for getkirby/cms, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update getkirby/cms to 4.9.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-34587 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-34587 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-34587. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-34587 in your dependencies?
O3 Security finds CVE-2026-34587 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.