CVE-2026-39312

HighPublic PoC

Published: 07 April 2026

Published

07 April 2026

Modified

14 April 2026

KEV Added

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Patch

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

EPSS Score 0.0029 52.1th percentile

Risk Priority 15 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-39312 is a high-severity Memory Allocation with Excessive Size Value (CWE-789) vulnerability in Softether Softethervpn. Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked in the top 47.9% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified are NIST 800-53 SC-5 (Denial-of-service Protection) and SI-10 (Information Input Validation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Application or System Exploitation (T1499.004). What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-2 Flaw Remediation good match

prevent

Flaw remediation directly mitigates this CVE by applying patches to SoftEther VPN Developer Edition to fix the vpnserver crash from malformed EAP-TLS packets over L2TP.

SC-5 Denial-of-service Protection good match

prevent

Denial-of-service protection implements rate limiting and traffic filtering on UDP/1701 to block malformed packets that crash the vpnserver process.

SI-10 Information Input Validation good match

prevent

Information input validation ensures the vpnserver rejects malformed EAP-TLS packets before processing, preventing the pre-authentication crash.

MITRE ATT&CK Enterprise TechniquesAI

T1499.004 Application or System Exploitation Impact

Adversaries may exploit software vulnerabilities that can cause an application or system to crash and deny availability to users.

attack.mitre.org →

Why these techniques?

Vulnerability enables remote unauthenticated crash of vpnserver process via malformed packet, directly mapping to Endpoint Denial of Service through Application or System Exploitation.

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

NVD Description

SoftEtherVPN is a an open-source cross-platform multi-protocol VPN Program. In 5.2.5188 and earlier, a pre-authentication denial-of-service vulnerability exists in SoftEther VPN Developer Edition 5.2.5188 (and likely earlier versions of Developer Edition). An unauthenticated remote attacker can crash the vpnserver process…

by sending a single malformed EAP-TLS packet over raw L2TP (UDP/1701), terminating all active VPN sessions.

Deeper analysisAI

CVE-2026-39312 is a pre-authentication denial-of-service vulnerability affecting SoftEther VPN Developer Edition version 5.2.5188 and likely earlier versions of the Developer Edition. SoftEtherVPN is an open-source cross-platform multi-protocol VPN program. The flaw resides in the vpnserver process, which can be crashed by processing a malformed EAP-TLS packet sent over raw L2TP on UDP port 1701.

An unauthenticated remote attacker can exploit this vulnerability by transmitting a single malformed EAP-TLS packet, resulting in the vpnserver process termination and disruption of all active VPN sessions. The CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) reflects network accessibility, low attack complexity, no privileges or user interaction required, and high availability impact with no confidentiality or integrity effects. It maps to CWE-789.

Mitigation details are available in the SoftEtherVPN security advisory published on GitHub at https://github.com/SoftEtherVPN/SoftEtherVPN/security/advisories/GHSA-q5g3-qhc6-pr3h.