CVE-2021-4026

Improper Access Control in bookstackapp/bookstack

6.5 MediumFix available

bookstack is vulnerable to Improper Access Control

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: Low
User interaction: None

What an attacker can affect

Confidentiality: High
Integrity: None
Availability: None

Exploit likelihood

0.93%Up 0.3 points since Dec 1, 2021

What each source reports

CVE List Score used 6.5

Improper Access Control in bookstackapp/bookstack

bookstack is vulnerable to Improper Access Control

Record: CVE-2021-4026
CVSS 3.0: 6.5 MediumCVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Weakness: CWE-284
Updated: 2026-11-02

EUVDEUVD-2021-2546 6.5

bookstack is vulnerable to Improper Access Control

Record: EUVD-2021-2546
CVSS 3.0: 6.5 MediumCVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Updated: 2026-11-03

GitHub AdvisoriesGHSA-jm6p-wfjg-xm7x 4.3

bookstack is vulnerable to Improper Access Control

bookstack is vulnerable to Improper Access Control.

Record: GHSA-jm6p-wfjg-xm7x
CVSS 3.1: 4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Weakness: CWE-284, CWE-863
Updated: 2026-11-02

NVD 4.3

bookstack is vulnerable to Improper Access Control

Record: CVE-2021-4026
CVSS 3.1: 4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
CVSS 3.0: 6.5 MediumCVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
CVSS 2.0: 4.0 MediumAV:N/AC:L/Au:S/C:P/I:N/A:N
Weakness: CWE-284, CWE-863
Updated: 2026-11-02

OSV 4.3

bookstack is vulnerable to Improper Access Control

Record: CVE-2021-4026
CVSS 3.1: 4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Updated: 2026-11-02

OSVGHSA-jm6p-wfjg-xm7x 4.3

bookstack is vulnerable to Improper Access Control

bookstack is vulnerable to Improper Access Control.

Record: GHSA-jm6p-wfjg-xm7x
CVSS 3.1: 4.3 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
Weakness: CWE-284, CWE-863
Updated: 2026-11-02

Affected products

Affected packages

Affected packages
Package	Affected	Fixed
`ssddanbrown/bookstack` Packagist	before 21.11.2	21.11.2
`ssddanbrown/bookstack` Packagist	before 21.11.2, plus listed versions 0.7.2V0.7.5v0.10.0v0.11.0v0.11.1 Show 45 moreShow less v0.11.2v0.12.0v0.12.1v0.12.2v0.13.0v0.13.1v0.14.0v0.14.1v0.14.2v0.14.3v0.15.0v0.15.1v0.15.2v0.15.3v0.16.0v0.16.1v0.16.2v0.16.3v0.17.0v0.17.1v0.17.2v0.17.3v0.17.4v0.18.0v0.18.1v0.18.2v0.18.3v0.18.4v0.18.5v0.19.0v0.20.0v0.20.1v0.20.2v0.20.3v0.21.0v0.22.0v0.23.0v0.23.1v0.23.2v0.24.0v0.24.1v0.24.2v0.24.3v0.25.0v0.25.1	21.11.2

History

History
Recorded	Changed	Sources
Nov 3, 2026	aliases	EUVD
Nov 2, 2026	first indexed	CVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-4026 is a medium vulnerability (CVSS 6.5) in Bookstackapp Bookstack, published November 30, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.93%, the 60th percentile. Fixed in ssddanbrown/bookstack 21.11.2.

References

This page doesn't list everything

Left out here: 81 versions. The JSON record has them.