CVE-2026-84695Network attack vectorHinoki check available

Stored XSS via unvalidated base64 drawing content

Published Sep 2, 2026 · Updated Sep 2, 2026

Stored cross-site scripting in BookStack before 26.05.4 allows remote authenticated users to execute scripts in administrator browsers. The drawing upload endpoint stores unvalidated base64 data as an image, and the gallery data route streams it inline without rejecting non-image MIME types. Editor permissions are required to upload a scripted SVG, and an administrator must access it through the image gallery API, exposing that browser session's data and actions.

CVSS severity8.7
High
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Stored cross-site scripting in BookStack before 26.05.4 allows remote authenticated users to execute scripts in administrator browsers. The drawing upload endpoint stores unvalidated base64 data as an image, and the gallery data route streams it inline without rejecting non-image MIME types. Editor permissions are required to upload a scripted SVG, and an administrator must access it through the image gallery API, exposing that browser session's data and actions.

The record

CVE
CVE-2026-84695
Published
Sep 2, 2026
Updated
Sep 2, 2026
Vendor
BookStack
Product
BookStack
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 2, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 2, 2026Record 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=0 <26.05.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

BookStack · BookStackversion=0 <26.05.4

Published CVSS scores

9.3VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N
8.7VulnCheckCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/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-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007Command and Scripting Interpreter: JavaScript/JScript

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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