CVE-2004-2375: Buffer overflow in the POP3 server in 1st Class Mail Server 4.0 allows remote attackers to cause a denial of s

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HIGH 7.5DOWNGRADE

CVE-2004-2375 is a high-severity flaw (CVSS 7.5) affecting 1st class mail server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Buffer overflow in the POP3 server in 1st Class Mail Server 4.0 allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via an APOP USER command with a long second parameter (digest).

Why this priority

High severity
EPSS top 7%: very likely to be exploited
Public exploit reference

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

Risk facts

CVSS score	7.5 (High)
EPSS exploit chance	5.9% (top 7%)
CISA exploited list	No
Published	2004-12-31
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: 1st class internet solutions

Last updated 2026-06-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2004-12-31 05:00 UTCPublished CVE record published
2026-06-16 22:09 UTCUpdated Record last modified

1st class internet solutions 1st class mail server DOWNGRADE

Affected: 4.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.0

1. Check installed version

apt-cache policy 1st-class-mail-server || rpm -q 1st-class-mail-server || 1st-class-mail-server --version

2. No fixed release: DOWNGRADE to a release before 4.0 (Debian / Ubuntu)

apt-cache madison 1st-class-mail-server sudo apt install 1st-class-mail-server=<VERSION_BEFORE_4.0> sudo apt-mark hold 1st-class-mail-server

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

dnf --showduplicates list 1st-class-mail-server sudo dnf downgrade 1st-class-mail-server-<VERSION_BEFORE_4.0> sudo dnf versionlock add 1st-class-mail-server

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.

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Exploit-DB: 1st Class Internet Solutions 1st Class Mail Server 4.0 - Remote Buffer Overflow (PoC)

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-2004-2375?

1st class mail server: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2004-2375 being exploited?

CVE-2004-2375 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-2004-2375 affect?

CVE-2004-2375 affects 1st class mail server. Severity is high (CVSS 7.5). Buffer overflow in the POP3 server in 1st Class Mail Server 4.0 allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via an APOP USER command with a long second parameter (digest).

How urgent is CVE-2004-2375?

Priority 55/100. High severity; EPSS top 7%: very likely to be exploited; Public exploit reference

Related CVEs

CVE-2004-2447 MEDIUM 4.3 DOWNGRADE Cross-site scripting (XSS) vulnerability in 1st Class Mail Server 4.01 allows remote attackers to inject arbit
CVE-2004-2446 MEDIUM 5.0 DOWNGRADE Directory traversal vulnerability in 1st Class Mail Server 4.01 allows remote attackers to read arbitrary file

References

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