CVE-2001-0402: IPFilter 3.4.16 and earlier does not include sufficient session information in its cache, which allows remote

Q: How do I fix CVE-2001-0402?

ipfilter: upgrade to newer than 3.4.16; freebsd: upgrade to newer than 4.1; openbsd: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2001-0402 being exploited?

CVE-2001-0402 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-2001-0402 affect?

CVE-2001-0402 affects ipfilter, freebsd, openbsd. Severity is high (CVSS 7.5). IPFilter 3.4.16 and earlier does not include sufficient session information in its cache, which allows remote attackers to bypass access restrictions by sending fragmented packets to a restricted port after sending unfragmented packets to a

Q: How urgent is CVE-2001-0402?

Priority 52/100. High severity; Public exploit reference

This month

HIGH 7.5UPGRADEUPGRADEMITIGATE

CVE-2001-0402 is a high-severity flaw (CVSS 7.5) affecting ipfilter, freebsd, openbsd. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

IPFilter 3.4.16 and earlier does not include sufficient session information in its cache, which allows remote attackers to bypass access restrictions by sending fragmented packets to a restricted port after sending unfragmented packets to an unrestricted port.

Why this priority

High severity
Public exploit reference

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
EPSS exploit chance	2.4% (top 16%)
CISA exploited list	No
Published	2001-06-18
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: darren reed · freebsd · openbsd

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

Am I affected?

Timeline

2001-06-18 04:00 UTCPublished CVE record published
2026-06-16 21:54 UTCUpdated Record last modified

darren reed ipfilter UPGRADE

Affected: <= 3.4.16

Fixed in: newer than 3.4.16

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to newer than 3.4.16 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade ipfilter

Note

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

freebsd freebsd UPGRADE

Affected: <= 4.1

Fixed in: newer than 4.1

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

openbsd openbsd MITIGATE

Affected: 2.8

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.8

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

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: IPFilter 3.x - Fragment Rule Bypass

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-2001-0402?

ipfilter: upgrade to newer than 3.4.16; freebsd: upgrade to newer than 4.1; openbsd: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2001-0402 being exploited?

CVE-2001-0402 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-2001-0402 affect?

CVE-2001-0402 affects ipfilter, freebsd, openbsd. Severity is high (CVSS 7.5). IPFilter 3.4.16 and earlier does not include sufficient session information in its cache, which allows remote attackers to bypass access restrictions by sending fragmented packets to a restricted port after sending unfragmented packets to a

How urgent is CVE-2001-0402?

Priority 52/100. High severity; Public exploit reference

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References

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