How severe is CVE-2009-3677?

CVE-2009-3677 has a CVSS 2.0 base score of 10.0, rated critical severity.

Is CVE-2009-3677 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 22% (97th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2009-3677?

CVE-2009-3677 primarily affects Microsoft Windows 2000. In total, 11 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2009-3677?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2009-3677 published?

CVE-2009-3677 was published on 2009-12-09 and last updated on 2026-06-16.

CVE-2009-3677

CVE-2009-3677 is a critical-severity vulnerability in Microsoft Windows 2000 with a CVSS 2.0 base score of 10.0. Its EPSS exploit-prediction score of 22% places it in the 97th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-94.

Key facts

Severity: Critical (CVSS 2.0 base score 10.0)
EPSS exploit prediction: 22% (97th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-94
Affected product: Microsoft Windows 2000
Published: 2009-12-09
Last modified: 2026-06-16

Description

The Internet Authentication Service (IAS) in Microsoft Windows 2000 SP4, XP SP2 and SP3, Server 2003 SP2, Vista Gold and SP1, and Server 2008 Gold does not properly verify the credentials in an MS-CHAP v2 Protected Extensible Authentication Protocol (PEAP) authentication request, which allows remote attackers to access network resources via a malformed request, aka "MS-CHAP Authentication Bypass Vulnerability."

Frequently asked questions

What is CVE-2009-3677?: The Internet Authentication Service (IAS) in Microsoft Windows 2000 SP4, XP SP2 and SP3, Server 2003 SP2, Vista Gold and SP1, and Server 2008 Gold does not properly verify the credentials in an MS-CHAP v2 Protected Extensible Authentication Protocol (PEAP) authentication request, which allows remote attackers to access network resources via a malformed request, aka "MS-CHAP Authentication Bypass Vulnerability."
How severe is CVE-2009-3677?: CVE-2009-3677 has a CVSS 2.0 base score of 10.0, rated critical severity.
Is CVE-2009-3677 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 22% (97th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2009-3677?: CVE-2009-3677 primarily affects Microsoft Windows 2000. In total, 11 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2009-3677?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2009-3677 published?: CVE-2009-3677 was published on 2009-12-09 and last updated on 2026-06-16.

References

Affected products (11)

cpe:2.3:o:microsoft:windows_2000:*:sp4:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2003:*:sp2:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2008:*:*:itanium:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2008:*:*:x32:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2008:*:*:x64:*:*:*:*:*
cpe:2.3:o:microsoft:windows_vista:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_vista:*:*:x64:*:*:*:*:*
cpe:2.3:o:microsoft:windows_vista:*:sp1:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_xp:*:sp2:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_xp:*:sp3:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_xp:-:sp2:x64:*:*:*:*:*

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