CVE-2026-54003: Kirby: External Initialization of the Panel on reverse proxy setups with the `Forwarded` header

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.7%, percentile 54: FIRST’s model estimates a 0.7% chance of exploitation activity in the next 30 days, higher than 54% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes getkirby/cms (Composer (PHP)) <= 4.9.3, fixed in 4.9.4; getkirby/cms (Composer (PHP)) >= 5.0.0-alpha.1, <= 5.4.3, fixed in 5.4.4. Check your lockfile, including transitive dependencies.

What it is

Kirby is an open-source content management system. Prior to 4.9.4 and from 5.4.4, Kirby sites with no configured user accounts that run on publicly accessible servers behind a reverse proxy setting the Forwarded, X-Client-IP, or X-Real-IP request header could allow remote attackers to install the Panel and create the first admin user because local-IP checks trusted those headers incorrectly. This issue is fixed in versions 4.9.4 and 5.4.4.

From the GitHub advisory

TL;DR

This vulnerability affects Kirby sites that have no configured user accounts and are running on publicly accessible servers behind a reverse proxy that sets the Forwarded: for=..., X-Client-IP, or X-Real-IP request header.

It was possible to install the Panel (= create the first admin user) in these setups even from remote IP addresses.

This vulnerability is of critical severity for affected sites.

Your site is not affected if any of the following apply:

Weakness type: CWE-454.

Product: getkirby/cms (Composer (PHP)) · Assigned by: GitHub_M · Published: 2026-07-09

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: present (depends on deployment conditions)
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.74% probability of exploitation activity in the next 30 days; percentile 54.

Timeline

• 2026-06-18 — GitHub-reviewed advisory GHSA-whxw-24jc-cwmv published (critical)
• 2026-07-09 — CVE record last updated
• 2026-07-09 — CVE record published by GitHub_M

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-whxw-24jc-cwmv github.com
2. CVE.org record CVE-2026-54003 cve.org
3. NVD entry CVE-2026-54003 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com
5. github.com github.com
6. github.com github.com
7. github.com github.com
8. github.com github.com

Critical Composer (PHP) advisories · Today’s Security Digest