CVE-2005-0066: The original design of TCP does not check that the TCP Acknowledgement number in an ICMP error message generat

This week

MEDIUM 5.0MITIGATE

CVE-2005-0066 is a medium-severity flaw (CVSS 5.0) affecting tcp. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The original design of TCP does not check that the TCP Acknowledgement number in an ICMP error message generated by an intermediate router is within the range of possible values for data that has already been acknowledged (aka "TCP acknowledgement number checking"), which makes it easier for attackers to forge ICMP error messages for specific TCP connections and cause a denial of service, as demonstrated using (1) blind connection-reset attacks w

Why this priority

EPSS top 4%: very likely to be exploited

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

Risk facts

CVSS score	5.0 (Medium)
EPSS exploit chance	10.7% (top 4%)
CISA exploited list	No
Published	2004-12-22
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: tcp

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

Am I affected?

Timeline

2004-12-22 05:00 UTCPublished CVE record published
2026-06-16 22:10 UTCUpdated Record last modified

tcp tcp MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

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

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

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-2005-0066?

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

Is CVE-2005-0066 being exploited?

CVE-2005-0066 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-2005-0066 affect?

CVE-2005-0066 affects tcp. Severity is medium (CVSS 5.0). The original design of TCP does not check that the TCP Acknowledgement number in an ICMP error message generated by an intermediate router is within the range of possible values for data that has already been acknowledged (aka "TCP acknowle

How urgent is CVE-2005-0066?

Priority 41/100. EPSS top 4%: very likely to be exploited

Related CVEs

CVE-2005-3675 HIGH 7.8 MITIGATE The Transmission Control Protocol (TCP) allows remote attackers to cause a denial of service (bandwidth consum
CVE-2005-0068 MEDIUM 5.0 MITIGATE The original design of ICMP does not require authentication for host-generated ICMP error messages, which make
CVE-2005-0067 MEDIUM 5.0 MITIGATE The original design of TCP does not require that port numbers be assigned randomly (aka "Port randomization"),
CVE-2005-0065 HIGH 10.0 MITIGATE The original design of TCP does not check that the TCP sequence number in an ICMP error message is within the
CVE-2004-1060 MEDIUM 5.0 MITIGATE MITIGATE Multiple TCP/IP and ICMP implementations, when using Path MTU (PMTU) discovery (PMTUD), allow remote attackers

References

← Back to latest CVEs