BookStack is vulnerable to Improper Access Control.

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS

• CVE-2021-4119: 26.89% estimated exploitation activity in the next 30 days; percentile 98.04 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.

Published by the source

16 Dec 2021, 19:40 UTC

Last modified by the source

30 Jan 2023, 05:02 UTC

Source last checked

26 Oct 2026, 14:00 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-9c5c-5j4h-8q2c

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# Patch Next advisory brief: CVE-2021-4119

Advisory: BookStack is vulnerable to Improper Access Control.
IDs: CVE-2021-4119, GHSA-9c5c-5j4h-8q2c
Record: https://patchnext.com/advisories/cve-2021-4119 (revision 1, source checked 26 Oct 2026, 14:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: ssddanbrown/bookstack 21.11.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist ssddanbrown/bookstack: affected < 21.11.3; fixed in 21.11.3

## Suggested inspection (read-only)
- Packagist ssddanbrown/bookstack: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on ssddanbrown/bookstack.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-9c5c-5j4h-8q2c (GitHub-reviewed advisory GHSA-9c5c-5j4h-8q2c lists affected ranges: Packagist ssddanbrown/bookstack >=0 <21.11.3)

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