CVE-2023-23581Network attack vector

Unauthenticated server crash via malformed HTTP header

Published Oct 12, 2023 · Updated Aug 2, 2024

Out-of-bounds read in SoftEther VPN 5.01.9674 and 5.02 allows remote attackers to crash vpnserver with a crafted HTTP header. EnSafeHttpHeaderValueStr removes an escaped newline by moving length minus index bytes from index plus two, reading one byte beyond the heap buffer. All configured TCP listeners parse HTTP by default, so no authentication is required; a carefully arranged heap boundary makes the server abort and interrupts VPN service until restart.

CVSS severity7.5
High
EPSS probability0.83%
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 SoftEther VPN 5.01.9674 and 5.02 allows remote attackers to crash vpnserver with a crafted HTTP header. EnSafeHttpHeaderValueStr removes an escaped newline by moving length minus index bytes from index plus two, reading one byte beyond the heap buffer. All configured TCP listeners parse HTTP by default, so no authentication is required; a carefully arranged heap boundary makes the server abort and interrupts VPN service until restart.

The record

CVE
CVE-2023-23581
Published
Oct 12, 2023
Updated
Aug 2, 2024
Vendor
SoftEther VPN Project
Product
SoftEther VPN
Classifications
CWE-125, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 12, 2023CVE publishedPublication date reported by the CVE source.
  2. Aug 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=5.01.9674
  2. Affected versionversion=5.02

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

SoftEther VPN Project · SoftEther VPNversion=5.01.9674; version=5.02

Published CVSS scores

7.5Cisco TalosCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-125Out-of-bounds Read
T1499.004Application or System Exploitation

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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