CVE-2023-40164Public exploit

Out-of-bounds read via unchecked character-class index

Published Aug 25, 2023 · Updated Oct 2, 2024

Out-of-bounds read in Notepad++ 8.5.6 and earlier allows attackers to access adjacent process memory after a crafted file is opened. In the bundled uchardet copy, nsCodingStateMachine::NextState uses a file-derived byteCls value of 9 to index the eight-entry ISO2022JPCharLenTable without validating the array bound. Exploitation requires a user to open the file, and the published proof of concept demonstrates a four-byte invalid read rather than extraction of memory contents.

CVSS severity5.5
Medium
EPSS probability0.50%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in Notepad++ 8.5.6 and earlier allows attackers to access adjacent process memory after a crafted file is opened. In the bundled uchardet copy, nsCodingStateMachine::NextState uses a file-derived byteCls value of 9 to index the eight-entry ISO2022JPCharLenTable without validating the array bound. Exploitation requires a user to open the file, and the published proof of concept demonstrates a four-byte invalid read rather than extraction of memory contents.

The record

CVE
CVE-2023-40164
Published
Aug 25, 2023
Updated
Oct 2, 2024
Vendor
Notepad++
Product
Notepad++
Classifications
CWE-120, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 25, 2023CVE publishedPublication date reported by the CVE source.
  2. Oct 2, 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=<= 8.5.6

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Notepad++ · Notepad++version=<= 8.5.6

Published CVSS scores

5.5GitHub CNACVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1204.002User Execution: Malicious File

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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