CVE-2000-0553: Race condition in IPFilter firewall 3.4.3 and earlier, when configured with overlapping "return-rst" and "keep

Routine

LOW 2.6DOWNGRADE

CVE-2000-0553 is a low-severity flaw (CVSS 2.6) affecting ipfilter. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Race condition in IPFilter firewall 3.4.3 and earlier, when configured with overlapping "return-rst" and "keep state" rules, allows remote attackers to bypass access restrictions.

Why this priority

Public exploit reference

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

Risk facts

CVSS score	2.6 (Low)
EPSS exploit chance	1.4% (top 27%)
CISA exploited list	No
Published	2000-05-26
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: darren reed

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

Am I affected?

Timeline

2000-05-26 04:00 UTCPublished CVE record published
2026-06-16 21:51 UTCUpdated Record last modified

darren reed ipfilter DOWNGRADE

Affected: 3.3.15 · 3.4.3

Fixed in: no fixed release known

Safe to downgrade to: a release before 3.3.15

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 3.3.15 (Debian / Ubuntu)

apt-cache madison ipfilter sudo apt install ipfilter=<VERSION_BEFORE_3.3.15> sudo apt-mark hold ipfilter

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

dnf --showduplicates list ipfilter sudo dnf downgrade ipfilter-<VERSION_BEFORE_3.3.15> sudo dnf versionlock add ipfilter

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-2000-0553?

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

Is CVE-2000-0553 being exploited?

CVE-2000-0553 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-2000-0553 affect?

CVE-2000-0553 affects ipfilter. Severity is low (CVSS 2.6). Race condition in IPFilter firewall 3.4.3 and earlier, when configured with overlapping "return-rst" and "keep state" rules, allows remote attackers to bypass access restrictions.

How urgent is CVE-2000-0553?

Priority 32/100. Public exploit reference

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References

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