CVE-2009-3677
HIGHEPSS 97th pctlDescription
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 to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v2 Vector
No CVSS vector data available.
Exploit Intelligence
Very high risk: more likely to be exploited than 97% of all known CVEs.
References
Related Vulnerabilities
Other CWE-94 (Code Injection) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2017-9841 | Critical | 9.8 | 100% | KEV | Fix |
| CVE-2015-1635 | Critical | 9.8 | 100% | KEV | - |
| CVE-2025-3248 | Critical | 9.8 | 100% | KEV + Ransom | Fix |
| CVE-2022-22954 | Critical | 9.8 | 100% | KEV + Ransom | - |
| CVE-2021-22204 | Medium | 6.8 | 100% | KEV | Fix |
| CVE-2012-0158 | High | 8.8 | 100% | KEV | - |
Common questions
How do I fix CVE-2009-3677?
No published fix for CVE-2009-3677 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2009-3677 being actively exploited?
Not that we know of. CVE-2009-3677 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 21.8% is the estimated probability that it will be exploited in the next 30 days. That is higher than 97% of all scored CVEs.
How severe is CVE-2009-3677?
CVE-2009-3677 has a CVSS v2 base score of 10.0, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-04-23.