CVE-2025-25566: Memory Leak vulnerability in SoftEtherVPN 5.02.5187 allows an attacker to cause a denial of service via the Un

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MEDIUM 5.6REMOTEDOWNGRADE

CVE-2025-25566 is a medium-severity flaw (CVSS 5.6) affecting vpn. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Memory Leak vulnerability in SoftEtherVPN 5.02.5187 allows an attacker to cause a denial of service via the UnixMemoryAlloc function. NOTE: the Supplier disputes this because the behavior is limited to a single allocation of a few hundred bytes with a command-line tool.

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	5.6 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 75%)
CISA exploited list	No
Weakness	CWE-401
Published	2025-03-12
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: softether

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-03-12 16:15 UTCPublished CVE record published
2026-06-17 09:00 UTCUpdated Record last modified

softether vpn DOWNGRADE

Affected: 5.02.5187

Fixed in: no fixed release known

Safe to downgrade to: a release before 5.02.5187

1. Check installed version

apt-cache policy vpn || rpm -q vpn || vpn --version

2. No fixed release: DOWNGRADE to a release before 5.02.5187 (Debian / Ubuntu)

apt-cache madison vpn sudo apt install vpn=<VERSION_BEFORE_5.02.5187> sudo apt-mark hold vpn

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list vpn sudo dnf downgrade vpn-<VERSION_BEFORE_5.02.5187> sudo dnf versionlock add vpn

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-25566?

vpn: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2025-25566 being exploited?

CVE-2025-25566 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-25566 affect?

CVE-2025-25566 affects vpn. Severity is medium (CVSS 5.6). Memory Leak vulnerability in SoftEtherVPN 5.02.5187 allows an attacker to cause a denial of service via the UnixMemoryAlloc function. NOTE: the Supplier disputes this because the behavior is limited to a single allocation of a few hundred b

How urgent is CVE-2025-25566?

Priority 36/100. Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2025-5687 HIGH 7.8 UPGRADE A vulnerability in Mozilla VPN on macOS allows privilege escalation from a normal user to root. *This bug only
CVE-2025-25568 CRITICAL 9.8 DOWNGRADE SoftEtherVPN 5.02.5187 is vulnerable to Use after Free in the Command.c file via the CheckNetworkAcceptThread
CVE-2025-25567 CRITICAL 9.8 DOWNGRADE SoftEther VPN 5.02.5187 is vulnerable to Buffer Overflow in Internat.c via the UniToStrForSingleChars function
CVE-2025-25565 CRITICAL 9.8 DOWNGRADE SoftEther VPN 5.02.5187 is vulnerable to Buffer Overflow in the Command.c file via the PtMakeCert and PtMakeCe

References

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