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Vulnerability record · CVE-2009-4445 · published 29 December 2009

CVE-2009-4445: Microsoft internet information services improper input validation vulnerability

Microsoft · Internet Information Services

Microsoft Internet Information Services (IIS), when used in conjunction with unspecified third-party upload applications, allows remote attackers to create empty files with arbitrary extensions via a filename containing an initial extension followed by a : (colon) and a safe extension, as demonstrated by an upload of a .asp:.jpg file that results in creation of an empty .asp file, related to support for the NTFS Alternate Data Streams (ADS) filename syntax. NOTE: it could be argued that this is a vulnerability in the third-party product, not IIS, because the third-party product should be applying its extension restrictions to the portion of the filename before the colon.

6.0 CVSS 2.0 Medium EPSS 13% · top 3.9% CWE-20 · Improper input validation
6.0CVSS 2.0 base score
13%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
6References
16 Jun 2026Last modified by NVD

Description

Microsoft Internet Information Services (IIS), when used in conjunction with unspecified third-party upload applications, allows remote attackers to create empty files with arbitrary extensions via a filename containing an initial extension followed by a : (colon) and a safe extension, as demonstrated by an upload of a .asp:.jpg file that results in creation of an empty .asp file, related to support for the NTFS Alternate Data Streams (ADS) filename syntax. NOTE: it could be argued that this is a vulnerability in the third-party product, not IIS, because the third-party product should be applying its extension restrictions to the portion of the filename before the colon.

AV:N/AC:M/Au:S/C:P/I:P/A:P

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://securitytracker.com/id?1023387 Third Party AdvisoryVDB Entry
http://soroush.secproject.com/downloadable/iis-semicolon-report.pdf Third Party Advisory
https://exchange.xforce.ibmcloud.com/vulnerabilities/55308
http://securitytracker.com/id?1023387 Third Party AdvisoryVDB Entry
http://soroush.secproject.com/downloadable/iis-semicolon-report.pdf Third Party Advisory
https://exchange.xforce.ibmcloud.com/vulnerabilities/55308

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2009-4445), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.