CVE-2024-38520Known exploitationPublic exploitNetwork attack vector

UDP traffic amplification via unmatched IPsec SA responses

Published Jun 26, 2024 · Updated Aug 2, 2024

Resource-consumption flaw in SoftEther VPN before 5.02.5185 allows remote attackers to amplify UDP traffic via crafted ISAKMP packets. ProcIPsecEspPacketRecv sends both an informational error and an IPsec SA deletion packet when a UDP/4500 packet names no existing SA. L2TP/IPsec must be enabled and reachable, and spoofed-source floods can exhaust reflector resources and multiply traffic toward a victim.

CVSS severity5.3
Medium
EPSS probability0.51%
Next 30 days · Sep 16, 2026
Known exploitationReported
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource-consumption flaw in SoftEther VPN before 5.02.5185 allows remote attackers to amplify UDP traffic via crafted ISAKMP packets. ProcIPsecEspPacketRecv sends both an informational error and an IPsec SA deletion packet when a UDP/4500 packet names no existing SA. L2TP/IPsec must be enabled and reachable, and spoofed-source floods can exhaust reflector resources and multiply traffic toward a victim.

The record

CVE
CVE-2024-38520
Published
Jun 26, 2024
Updated
Aug 2, 2024
Vendor
SoftEther VPN Project
Product
SoftEther VPN
Classifications
CWE-400, T1498.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 26, 2024CVE 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=<= 5.02.5183
  2. Affected versionversion=5.02.5185

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

SoftEther VPN Project · SoftEther VPNversion=<= 5.02.5183; version=5.02.5185

Published CVSS scores

5.3GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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
Privilegesunauthenticated
Known exploitationReported
Public exploitPublished

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1498.002Reflection Amplification

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Reported exploitation

Technologies

Your stack

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Your stack

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