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MEDIUM severity

BookStack is vulnerable to Improper Access ControlGHSA-9c5c-5j4h-8q2c

MEDIUMFix: bookstackapp/bookstack@e765e61

GHSA-9c5c-5j4h-8q2c is a medium-severity (CVSS 5.3) 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.

Also known asCVE-2021-4119
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
1 known
Exploitation data as of Oct 12, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
26.9%probability of exploitation in next 30 days
Moderate Risk0.00%
Lower risk than most CVEs98th percentile — riskier than 98% of all scored CVEsHighest risk
0.00%11.6%23.2%34.8%0.4%26.9%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

GHSA-9c5c-5j4h-8q2c 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

1 pkg affected
🐘ssddanbrown/bookstack

Real-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

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐘Packagistssddanbrown/bookstackall versions21.11.3composer require ssddanbrown/bookstack:^21.11.3

Affected Products

1 product · 1 configurations
Application
bookstackbookstackapp
≤ 21.11.2
range
Exploits & PoCs
1

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

bookstack is vulnerable to Improper Access Control

huntr.devNVDDec 2021

Detection & mitigation playbook

Open-source dependency

  1. Detect

    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.

  2. Fix

    Update ssddanbrown/bookstack to 21.11.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-9c5c-5j4h-8q2c is resolved across your whole dependency graph.

  3. 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

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.
O3 Security · Impact-Aware SCA

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BookStack is vulnerable to Improper Access Control