[VulnWatch] NSFOCUS SA2003-05: Microsoft IIS ssinc.dll Over-long Filename Buffer Overflow Vulnerability
From: NSFOCUS Security Team (security_at_nsfocus.com)
To: firstname.lastname@example.org Date: Fri, 30 May 2003 22:01:17 +0800
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NSFOCUS Security Advisory(SA2003-05)
Topic: Microsoft IIS ssinc.dll Over-long Filename Buffer Overflow Vulnerability
Release Date: 2003-5-30
CVE CAN ID: CAN-2003-0224
- - Microsoft IIS 5.0
- - Microsoft IIS 4.0
- - Microsoft IIS 5.1
NSFOCUS Security Team has found a buffer overflow vulnerability in the way
a dynamic linking library (ssinc.dll)that is shipped with Microsoft IIS 4.0/5.0
handles the files it contains. Exploiting the vulnerability local attackers
could gain local system privilege.
Microsoft IIS supports SSI(Server Side Include) functionality. ssinc.dll is
a SSI interpreter. By default extended name .stm,.shtm and .shtml will be
mapped to interpreter(ssinc.dll).
SSI supports "#include" command. Typically it is used as the following:
When handling "#include" command ssinc.dll will first attempt to gain the
physical path of the shtml file, so it will copy the URI request to a buffer
the size of which is fixed. For example, when requesting the following
It will copy "/abc/test.shtml" to a buffer the size of which is fixed. Because
the length of the shtml filename has not been checked during the copying,
it causes a stack buffer overflow.
NSFocus Security Team has found a similar problem. See
The corresponding Microsoft Security Bulletin is:
This vulnerability occurred before that one.
IIS has checked the over-long shtml filename to avoid buffer overflow,
while its method is to shorten the filename to legal length, then attempt
to open it. After that ssinc.dll will still use the original URI to finish
the copy. Therefore, by creating a WEB file with special length local attackers
could bypass the check, then request a shtml file with an over-long filename
to cause a buffer overflow, which would cause IIS cease to respond. By carefully
crafting the overflow data attackers could run arbitrary code with Local System
Two conditions are required to carry out the attack:
1. Attackers need to have the privilege to create files on web directory.
2. Attackers need to be able to access the created files via web service.
1. Disable untrusted users' writing privilege to web directory.
2. If SSI functionality is not required, remove .shtml, .shtm, .stm mapping.
3. Install IIS Lockdown tools provided by Microsoft:
2002.11.05 Inform vendor about the issue
2003.05.28 Microsoft has issued a Security Bulletin(MS03-018) and the related patch.
Detailed Microsoft Security Bulletin is available at:
Patches are available at:
The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2003-0224 to this issue. This is a candidate for inclusion in the
CVE list (http://cve.mitre.org), which standardizes names for security
problems. Candidates may change significantly before they become official
This vulnerability was discovered by Ren Guang Yuan of NSFOCUS Security Team.
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NSFOCUS Security Team <email@example.com>
NSFOCUS INFORMATION TECHNOLOGY CO.,LTD
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