CVE-2021-4119 is a critical-severity (CVSS 9.8) CWE-284 vulnerability in ssddanbrown/bookstack. 1 public exploit reference exists, so weaponization risk is real. A fix is available for ssddanbrown/bookstack — see the affected versions and patch details below.
BookStack is vulnerable to Improper Access Control.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-4119 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,987 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
ssddanbrown/bookstackReal-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
BookStack prior to version 21.11.3 is vulnerable to Improper Access Control. A logged-in user with no privileges OR guest user (if public access enabled) can access the /search/users/select AJAX endpoint meant for admins to manage audit logs, to dump all usernames existing in the Bookstack database. This can also be used to harvest email belonging to a user because BookStack also uses the code where(email, like, % . $search . %) to search for users based on email.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | ssddanbrown/bookstack | all versions | 21.11.3composer require ssddanbrown/bookstack:^21.11.3 |
Affected Products
bookstackbookstackappResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ssddanbrown/bookstack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update ssddanbrown/bookstack to 21.11.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-4119 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.
Frequently Asked Questions
Is CVE-2021-4119 in your dependencies?
Find it across Packagist, including transitive dependencies.