CVE-2008-4609: The TCP implementation in (1) Linux, (2) platforms based on BSD Unix, (3) Microsoft Windows, (4) Cisco product

This week

HIGH 7.1WATCHLISTMITIGATEMITIGATEMITIGATE

CVE-2008-4609 is a high-severity flaw (CVSS 7.1) affecting bsd, bsd os, ios. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The TCP implementation in (1) Linux, (2) platforms based on BSD Unix, (3) Microsoft Windows, (4) Cisco products, and probably other operating systems allows remote attackers to cause a denial of service (connection queue exhaustion) via multiple vectors that manipulate information in the TCP state table, as demonstrated by sockstress.

Why this priority

High severity
EPSS top 2%: very likely to be exploited
On your watchlist

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

Risk facts

CVSS score	7.1 (High)
EPSS exploit chance	32.4% (top 2%)
CISA exploited list	No
Weakness	CWE-16
Published	2008-10-20
Last modified	2026-06-16

Publisher (CNA): MITRE · Vendor: bsd · bsdi · cisco · dragonflybsd · freebsd · linux

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

Am I affected?

Timeline

2008-10-20 17:59 UTCPublished CVE record published
2026-06-16 22:58 UTCUpdated Record last modified

bsd bsd MITIGATE

Affected: all versions · 4.1 · 4.2 · 4.3 · 4.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.1

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.

bsdi bsd os MITIGATE

Affected: all versions · 1.1 · 2.0 · 2.0.1 · 2.1 · 3.0 · 3.1 · 3.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.1

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.

cisco ios MITIGATE

Affected: all versions · 4.1 · 4.1.1 · 4.1.2 · 8.2 · 8.3 · 9.0 · 9.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.1

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.

dragonflybsd dragonflybsd MITIGATE

Affected: all versions · 1.0 · 1.1 · 1.2 · 1.10.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.0

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.

freebsd freebsd MITIGATE

Affected: all versions · 0.4_1 · 1.0 · 1.1 · 1.1.5 · 1.1.5.1 · 1.2 · 1.5

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.4_1

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.

linux linux kernel MITIGATE

Affected: all versions · 1.2.0 · 1.3.0 · 2.0 · 2.0.1 · 2.0.2 · 2.0.3 · 2.0.4

Fixed in: no fixed release known

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.

Downgrade not recommended

This is a core system component: downgrading can break the OS. Apply the distro update or the vendor mitigation.

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-2008-4609?

bsd: mitigate or apply the listed mitigation; bsd os: mitigate or apply the listed mitigation; ios: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2008-4609 being exploited?

CVE-2008-4609 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-2008-4609 affect?

CVE-2008-4609 affects bsd, bsd os, ios. Severity is high (CVSS 7.1). The TCP implementation in (1) Linux, (2) platforms based on BSD Unix, (3) Microsoft Windows, (4) Cisco products, and probably other operating systems allows remote attackers to cause a denial of service (connection queue exhaustion) via mul

How urgent is CVE-2008-4609?

Priority 54/100. High severity; EPSS top 2%: very likely to be exploited; On your watchlist

Software pages

Windows vulnerabilities · Linux kernel vulnerabilities · iOS vulnerabilities · Cisco vulnerabilities

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References

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