CVE-2021-4026Network attack vector

Draft attachment disclosure via missing ownership filter

Published Nov 30, 2021 · Updated Aug 3, 2024

Incorrect authorization in BookStack before 21.11.2 allows remote authenticated users to read attachments on another user's draft page. The related-entity filters in PermissionService apply saved-page view permissions without also checking a draft page's owner, so the attachment API returns draft-linked items to nonowners. A valid API account with permission to view the eventual saved page is required; impact is limited to disclosure of draft-related content.

CVSS severity4.3
Medium
EPSS probability0.90%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect authorization in BookStack before 21.11.2 allows remote authenticated users to read attachments on another user's draft page. The related-entity filters in PermissionService apply saved-page view permissions without also checking a draft page's owner, so the attachment API returns draft-linked items to nonowners. A valid API account with permission to view the eventual saved page is required; impact is limited to disclosure of draft-related content.

The record

CVE
CVE-2021-4026
Published
Nov 30, 2021
Updated
Aug 3, 2024
Vendor
BookStack
Product
BookStack
Classifications
CWE-863, CWE-284, T1213
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Nov 30, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <21.11.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

BookStack · BookStackversion=unspecified <21.11.2

Published CVSS scores

6.5huntr.devCVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-863Incorrect Authorization
CWE-284Improper Access Control
T1213Data from Information Repositories

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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