CVE-2009-4444: Microsoft Internet Information Services

Medium severity, CVSS 6.0. EPSS: 63.6% chance of exploitation in the next 30 days.

Microsoft Internet Information Services (IIS) 5.x and 6.x uses only the portion of a filename before a ; (semicolon) character to determine the file extension, which allows remote attackers to bypass intended extension restrictions of third-party upload applications via a filename with a (1) .asp, (2) .cer, or (3) .asa first extension, followed by a semicolon and a safe extension, as demonstrated by the use of asp.dll to handle a .asp;.jpg file.

Affected products

• Microsoft Internet Information Services: version 5.0 only; version 6.0 only

Published 2009-12-29. Last modified 2026-06-16.