CVE-2026-55105Network attack vector

Script execution via unsanitized Fountain renderer output

Published Sep 21, 2026 · Updated Sep 21, 2026

Cross-site scripting in Joplin before 3.6.15 and 3.7.0 through 3.7.1 allows attackers to execute script via Fountain code blocks. packages/renderer/MdToHtml/rules/fountain.ts inserts HTML returned by the vendored fountain.js renderer into note output without sanitization. Fountain rendering must be enabled in a desktop or mobile client, while published notes on Joplin Server enable it by default; the script can read later note-viewer content or authenticated browser data in the server origin.

CVSS severityUnavailable
Unscored
EPSS probability0.50%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Joplin before 3.6.15 and 3.7.0 through 3.7.1 allows attackers to execute script via Fountain code blocks. packages/renderer/MdToHtml/rules/fountain.ts inserts HTML returned by the vendored fountain.js renderer into note output without sanitization. Fountain rendering must be enabled in a desktop or mobile client, while published notes on Joplin Server enable it by default; the script can read later note-viewer content or authenticated browser data in the server origin.

The record

CVE
CVE-2026-55105
Published
Sep 21, 2026
Updated
Sep 21, 2026
Vendor
Joplin Project
Product
Joplin
Classifications
T1203
Attack vector
network
Privileges
Unavailable

Timeline

How it unfolded

  1. Sep 21, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 21, 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=< 3.6.15
  2. Affected versionversion=>= 3.7.0, < 3.7.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesUnavailable in this record.

What is affected?

Joplin Project · Joplinversion=< 3.6.15; version=>= 3.7.0, < 3.7.2

Published CVSS scores

No CVSS assessment is available in this record.

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.

Activity data is delayed. The latest report is Sep 28, 2026.

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

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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