CVE-2025-25567: SoftEther VPN 5.02.5187 is vulnerable to Buffer Overflow in Internat.c via the UniToStrForSingleChars function

This week

CRITICAL 9.8REMOTEDOWNGRADE

CVE-2025-25567 is a critical-severity flaw (CVSS 9.8) affecting vpn. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

SoftEther VPN 5.02.5187 is vulnerable to Buffer Overflow in Internat.c via the UniToStrForSingleChars function. NOTE: the Supplier disputes this because the behavior only enables a local user to attack himself through the UI,

Why this priority

Critical severity
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	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 51%)
CISA exploited list	No
Weakness	CWE-120
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-2025-25567?

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

Is CVE-2025-25567 being exploited?

CVE-2025-25567 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-2025-25567 affect?

CVE-2025-25567 affects vpn. Severity is critical (CVSS 9.8). SoftEther VPN 5.02.5187 is vulnerable to Buffer Overflow in Internat.c via the UniToStrForSingleChars function. NOTE: the Supplier disputes this because the behavior only enables a local user to attack himself through the UI,

How urgent is CVE-2025-25567?

Priority 56/100. Critical severity; 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-2025-25566 MEDIUM 5.6 DOWNGRADE Memory Leak vulnerability in SoftEtherVPN 5.02.5187 allows an attacker to cause a denial of service via the Un
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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