CVE-2011-0661

CVE-2011-0661 is a critical-severity vulnerability in Microsoft Windows 2003 Server with a CVSS 2.0 base score of 10.0. Its EPSS exploit-prediction score of 45% places it in the 99th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-20.

Key facts

• Severity: Critical (CVSS 2.0 base score 10.0)
• EPSS exploit prediction: 45% (99th percentile)
• Actively exploited: Not listed in CISA KEV
• Weakness: CWE-20
• Affected product: Microsoft Windows 2003 Server
• Published: 2011-04-13
• Last modified: 2026-06-16

Description

The SMB Server service in Microsoft Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista SP1 and SP2, Windows Server 2008 Gold, SP2, R2, and R2 SP1, and Windows 7 Gold and SP1 does not properly validate fields in SMB requests, which allows remote attackers to execute arbitrary code via a malformed request in a (1) SMBv1 or (2) SMBv2 packet, aka "SMB Transaction Parsing Vulnerability."

Frequently asked questions

What is CVE-2011-0661?

The SMB Server service in Microsoft Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista SP1 and SP2, Windows Server 2008 Gold, SP2, R2, and R2 SP1, and Windows 7 Gold and SP1 does not properly validate fields in SMB requests, which allows remote attackers to execute arbitrary code via a malformed request in a (1) SMBv1 or (2) SMBv2 packet, aka "SMB Transaction Parsing Vulnerability."

How severe is CVE-2011-0661?

CVE-2011-0661 has a CVSS 2.0 base score of 10.0, rated critical severity.

Is CVE-2011-0661 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 45% (99th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2011-0661?

CVE-2011-0661 primarily affects Microsoft Windows 2003 Server. In total, 17 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2011-0661?

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-2011-0661 published?

CVE-2011-0661 was published on 2011-04-13 and last updated on 2026-06-16.

References

• http://osvdb.org/71781
• http://secunia.com/advisories/44072
• http://www.securityfocus.com/bid/47198
• http://www.securitytracker.com/id?1025329
• http://www.us-cert.gov/cas/techalerts/TA11-102A.html
• http://www.vupen.com/english/advisories/2011/0939
• https://docs.microsoft.com/en-us/security-updates/securitybulletins/2011/ms11-020
• https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A12076

Affected products (17)

• cpe:2.3:o:microsoft:windows_2003_server:*:sp2:*:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_7:-:*:*:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_7:-:sp1:x64:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_7:-:sp1:x86:*:*:*:*:*
• 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_server_2008:*:sp2:x32:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_server_2008:*:sp2:x64:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_server_2008:-:sp2:itanium:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_server_2008:r2:*:itanium:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_server_2008:r2:*:x64:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_vista:*:sp1:*:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_vista:*:sp2:*:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_xp:*:sp3:*:*:*:*:*:*
• cpe:2.3:o:microsoft:windows_xp:-:sp2:x64:*:*:*:*:*

More vulnerabilities in Microsoft Windows 2003 Server

• CVE-2011-1868 — Critical (CVSS 10.0): The Distributed File System (DFS) implementation in Microsoft Windows XP SP2 and SP3 and Server 2003 SP2 does not…
• CVE-2011-1268 — Critical (CVSS 10.0): The SMB client in Microsoft Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista SP1 and SP2, Windows Server…
• CVE-2011-0654 — Critical (CVSS 10.0): Integer underflow in the BowserWriteErrorLogEntry function in the Common Internet File System (CIFS) browser service in…
• CVE-2010-2550 — Critical (CVSS 10.0): The SMB Server in Microsoft Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista SP1 and SP2, Windows Server…
• CVE-2010-0476 — Critical (CVSS 10.0): The SMB client in Microsoft Windows Server 2003 SP2, Vista Gold, SP1, and SP2, and Windows Server 2008 Gold and SP2…
• CVE-2010-0269 — Critical (CVSS 10.0): The SMB client in Microsoft Windows 2000 SP4, Windows XP SP2 and SP3, Windows Server 2003 SP2, Windows Vista Gold, SP1,…

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