CVE-2026-34587: Kirby has Server-Side Template Injection (SSTI) via double template resolution in option rendering

high Affects getkirby/cms. Feed 2026.10.29.1, updated 2026-10-28; published 2026-04-23; advisory modified 2026-05-05.

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

Package: getkirby/cms Composer
Affected versions: <4.9.0 or >=5.0.0 and <5.4.0
Fixed in: 4.9.0, 5.4.0
Severity: high CVSS 8.1
Exploitation: not on CISA KEV · EPSS 0% (26.7th percentile)
Published: 2026-04-23
Source: osv.dev

References

Am I affected?

Find out in one command. phpwarden checks your composer.lock against this advisory and 20,000+ others, ranked by real-world exploitation (CISA KEV + EPSS). Free, offline, open data.

# one-time install
pip install phpwarden

# then
phpwarden deps composer.lock

Or keep it checked automatically: GitHub Action · pre-commit hook · GitLab CI · Laravel artisan command

Install docs How findings are ranked

Related advisories

CVE-2021-29460 high Cross-site scripting (XSS) from unsanitized uploaded SVG files in Kirby same package: getkirby/cms
CVE-2017-16807 medium Kirby XSS Vulnerability same package: getkirby/cms
CVE-2026-44177 high Kirby CMS has pre-authentication path traversal and PHP file inclusion during user lookup same package: getkirby/cms
CVE-2023-38490 medium XML External Entity (XXE) vulnerability in the XML data handler same package: getkirby/cms
CVE-2020-26255 medium Kirby Panel users could upload PHP Phar archives as content files before v2.5.14 and v3.4. same package: getkirby/cms
CVE-2023-38492 medium Denial of service from unlimited password lengths same package: getkirby/cms