CVE-2025-34491: GFI MailEssentials prior to version 21.8 is vulnerable to a .NET deserialization issue

Q: How do I fix CVE-2025-34491?

mailessentials: upgrade to 21.8. Exact commands for each OS are on this page.

Q: Is CVE-2025-34491 being exploited?

CVE-2025-34491 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2025-34491 affect?

CVE-2025-34491 affects mailessentials. Severity is high (CVSS 8.8). GFI MailEssentials prior to version 21.8 is vulnerable to a .NET deserialization issue. A remote and authenticated attacker can execute arbitrary code by sending crafted serialized .NET when joining to a Multi-Server setup.

Q: How urgent is CVE-2025-34491?

Priority 51/100. High severity; Public exploit reference

This month

HIGH 8.8UPGRADE

CVE-2025-34491 is a high-severity flaw (CVSS 8.8) affecting mailessentials. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

GFI MailEssentials prior to version 21.8 is vulnerable to a .NET deserialization issue. A remote and authenticated attacker can execute arbitrary code by sending crafted serialized .NET when joining to a Multi-Server setup.

Why this priority

High severity
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	1.0% (top 38%)
CISA exploited list	No
Weakness	CWE-502
Published	2025-04-28
Last modified	2026-06-17

Publisher (CNA): VulnCheck · Vendor: gfi

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

Am I affected?

Timeline

2025-04-28 20:15 UTCPublished CVE record published
2026-06-17 09:14 UTCUpdated Record last modified

gfi mailessentials UPGRADE

Affected: < 21.8

Fixed in: 21.8

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 21.8 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mailessentials

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mailessentials

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2025-34491?

mailessentials: upgrade to 21.8. Exact commands for each OS are on this page.

Is CVE-2025-34491 being exploited?

CVE-2025-34491 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-2025-34491 affect?

CVE-2025-34491 affects mailessentials. Severity is high (CVSS 8.8). GFI MailEssentials prior to version 21.8 is vulnerable to a .NET deserialization issue. A remote and authenticated attacker can execute arbitrary code by sending crafted serialized .NET when joining to a Multi-Server setup.

How urgent is CVE-2025-34491?

Priority 51/100. High severity; Public exploit reference

Related CVEs

CVE-2025-34490 MEDIUM 6.5 UPGRADE GFI MailEssentials prior to version 21.8 is vulnerable to an XML External Entity (XXE) issue
CVE-2025-34489 HIGH 7.8 UPGRADE GFI MailEssentials prior to version 21.8 is vulnerable to a local privilege escalation issue

References

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