GHSA-c27j-76xg-6x4f
MEDIUMKirby CMS vulnerable to user enumeration in the brute force protection
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.
Blast Radius
getkirby/cms🐘getkirby/cms🐘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 with user accounts (unless Kirby's API and Panel are disabled in the config). It can only be exploited for targeted attacks because the attack does not scale to brute force.
Introduction
User enumeration is a type of vulnerability that allows attackers to confirm which users are registered in a Kirby installation. This information can be abused for social engineering attacks against users of the site or to find out the organizational structure of the company.
User enumeration attacks are performed by entering an existing and a non-existing user into the email address field of the login form. If the system returns a different response or behaves differently depending on whether the user exists, the attacker can enter unknown email addresses and use the different behavior as a clue for the (non-)existing user.
Impact
Kirby comes with a built-in brute force protection. By default, it will prevent further login attempts after 10 failed logins from a single IP address or of a single existing user. After every failed login attempt, Kirby inserts a random delay between one millisecond and two seconds to make automated attacks harder and to avoid leaking whether the user exists. Unfortunately, this random delay was not inserted after the brute force limit was reached.
Because Kirby only tracks failed login attempts per email address for existing users but always tracks failed login attempts per IP address, this behavior could be abused by attackers for user enumeration. For this to work, an attacker would need to create login requests beyond the trials limit (which is 10 by default) from two or more IP addresses. After the trials limit was reached, the login form immediately blocked further requests for existing users, but not for invalid users.
This exploit does not scale to brute force attacks because of the delay during the first 10 requests per user, the faint difference between the responses for valid and invalid users and the fact that code-based logins would send an email for every login attempt, which makes the attack easy to spot. The vulnerability is therefore only relevant for targeted attacks.
Patches
The problem has been patched in Kirby 3.5.8.2, Kirby 3.6.6.2, Kirby 3.7.5.1 and Kirby 3.8.1. Please update to one of these or a later version to fix the vulnerability.
In all of the mentioned releases, we have rewritten the affected code so that the delay is also inserted after the brute force limit is reached.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | getkirby/cms | all versions | 3.5.8.2 |
| 🐘Packagist | getkirby/cms | ≥ 3.6.0&&< 3.6.6.2 | 3.6.6.2 |
| 🐘Packagist | getkirby/cms | ≥ 3.7.0&&< 3.7.5.1 | 3.7.5.1 |
| 🐘Packagist | getkirby/cms | ≥ 3.8.0&&< 3.8.1 | 3.8.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for getkirby/cms. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update getkirby/cms to 3.5.8.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-c27j-76xg-6x4f 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 pinpoints whether GHSA-c27j-76xg-6x4f is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-c27j-76xg-6x4f. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-c27j-76xg-6x4f in your dependencies?
O3 detects GHSA-c27j-76xg-6x4f across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.