CVE-2026-40263Public exploitNetwork attack vector

Username enumeration via unequal bcrypt verification timing

Published Apr 16, 2026 · Updated Apr 16, 2026

Observable timing discrepancy in Note Mark 0.19.1 and earlier allows remote attackers to enumerate usernames through login requests. The POST /api/auth/token path runs bcrypt.CompareHashAndPassword only when the queried username exists and otherwise returns without an equivalent bcrypt operation. Network access to the exposed login endpoint is sufficient; repeated response-time measurements disclose account existence and support targeted credential attacks.

CVSS severity3.7
Low
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Observable timing discrepancy in Note Mark 0.19.1 and earlier allows remote attackers to enumerate usernames through login requests. The POST /api/auth/token path runs bcrypt.CompareHashAndPassword only when the queried username exists and otherwise returns without an equivalent bcrypt operation. Network access to the exposed login endpoint is sufficient; repeated response-time measurements disclose account existence and support targeted credential attacks.

The record

CVE
CVE-2026-40263
Published
Apr 16, 2026
Updated
Apr 16, 2026
Vendor
Leo Spratt
Product
Note Mark
Classifications
CWE-208, T1087
Attack vector
network
Privileges
unauthenticated

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 privilegesunauthenticated

What is affected?

Leo Spratt · Note Markversion=< 0.19.2

Published CVSS scores

3.7GitHubCVSS:3.1/AV:N/AC:H/PR:N/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.

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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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-208Observable Timing Discrepancy
T1087Account Discovery

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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