CVE-2026-40262Public exploitNetwork attack vector

Stored XSS via sniffed inline assets

Published Apr 16, 2026 · Updated Apr 16, 2026

Stored XSS in Note Mark 0.19.1 and earlier allows remote authenticated users to execute JavaScript via a malicious note asset. The asset delivery handler uses magic-byte detection that leaves HTML, SVG, and XHTML untyped, serves them inline, and omits nosniff, so browsers execute embedded scripts under the application origin. Exploitation requires a low-privilege uploader and a victim opening the asset URL, exposing private notes and authenticated API actions.

CVSS severity8.7
High
EPSS probability0.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in Note Mark 0.19.1 and earlier allows remote authenticated users to execute JavaScript via a malicious note asset. The asset delivery handler uses magic-byte detection that leaves HTML, SVG, and XHTML untyped, serves them inline, and omits nosniff, so browsers execute embedded scripts under the application origin. Exploitation requires a low-privilege uploader and a victim opening the asset URL, exposing private notes and authenticated API actions.

The record

CVE
CVE-2026-40262
Published
Apr 16, 2026
Updated
Apr 16, 2026
Vendor
Leo Spratt
Product
Note Mark
Classifications
CWE-434, CWE-79, T1189
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 16, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 16, 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=< 0.19.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Leo Spratt · Note Markversion=< 0.19.2

Published CVSS scores

8.7GitHubCVSS: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 exploitPublished

Weakness, pattern, technique

CWE-434Unrestricted Upload of File with Dangerous Type
CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1189Drive-by Compromise

Public exploit references

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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