CVE-2023-30328: An issue in the helper tool of Mailbutler GmbH Shimo VPN Client for macOS v5.0.4 allows attackers to bypass au

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CRITICAL 9.8REMOTEDOWNGRADE

CVE-2023-30328 is a critical-severity flaw (CVSS 9.8) affecting shimo. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue in the helper tool of Mailbutler GmbH Shimo VPN Client for macOS v5.0.4 allows attackers to bypass authentication via PID re-use.

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	1.1% (top 35%)
CISA exploited list	No
Weakness	CWE-287
Published	2023-05-04
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: mailbutler

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

Am I affected?

Timeline

2023-05-04 21:15 UTCPublished CVE record published
2026-06-17 05:54 UTCUpdated Record last modified

mailbutler shimo DOWNGRADE

Affected: 5.0.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 5.0.4

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 5.0.4 (Debian / Ubuntu)

apt-cache madison shimo sudo apt install shimo=<VERSION_BEFORE_5.0.4> sudo apt-mark hold shimo

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

dnf --showduplicates list shimo sudo dnf downgrade shimo-<VERSION_BEFORE_5.0.4> sudo dnf versionlock add shimo

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-2023-30328?

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

Is CVE-2023-30328 being exploited?

CVE-2023-30328 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-2023-30328 affect?

CVE-2023-30328 affects shimo. Severity is critical (CVSS 9.8). An issue in the helper tool of Mailbutler GmbH Shimo VPN Client for macOS v5.0.4 allows attackers to bypass authentication via PID re-use.

How urgent is CVE-2023-30328?

Priority 61/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

macOS vulnerabilities

References

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