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Title: Flaw in Services for Unix 3.0 Interix SDK Could Allow
Code Execution (Q329209)
Released: 02 October 2002
Software: Services for Unix 3.0 Interix SDK
Impact: Buffer overrun and denial of service
Max Risk: Moderate
Bulletin: MS02-057

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS02-057.asp.

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Issue:

All three vulnerabilities discussed in this bulletin involve the
inclusion of the Sun [TM] Microsystems RPC library in Microsoft's
Services for UNIX (SFU) 3.0 on the Interix SDK. Developers who
created applications or utilities using the Sun RPC library from
the Interix SDK need to evaluate three vulnerabilities.

Windows Services for UNIX (SFU) 3.0 provides a full range of cross-
platform services to integrate Windows into existing UNIX environ-
ments. In version 3.0, the Interix subsystem technology is built in
so that Windows Services for UNIX 3.0 can provide platform inter-
operability and application migration in one fully integrated and
supported product from Microsoft. Developers who have integrated
Windows into their existing UNIX environments may have used the
Interix SDK to develop custom applications and utilities so that
applications that only ran on the UNIX platform can now run in a
Windows environment. Developers who used the Interix SDK to develop
applications or utilities should read this bulletin.

The first vulnerability is an integer overflow in the XDR library
that ships with the Sun RPC library on the Interix SDK for
Microsoft's Services for Unix (SFU) 3.0. An attacker could send a
malicious RPC request to the RPC server from a remote machine and
cause corruption in the server program. This can cause the server
to fail and potentially allow the attacker to run code of his or
her choice in the context of the server program.

The second vulnerability is a buffer overrun. An attacker could send
a malicious RPC request to the RPC server with an improper parameter
size check. This could lead to a buffer overrun, causing the server
to fail and preventing it from servicing any further requests from
clients.

The third vulnerability is an RPC implementation error. An app-
Lication using the Sun RPC library does not properly check the size
of client TCP requests. This could result in a denial of service
to a server application using the Sun RPC library. The RPC library
expects client TCP requests to specify the size of the record
that follows. Because there is a flaw in the way RPC detects
client packets, an attacker could send a malformed RPC request to
the RPC server from a remote machine and cause the server to fail
by not servicing any further client requests.

After applying the patch, it is necessary to recompile any Interix
application that is statically linked with the Interix SDK Sun RPC
library.

Mitigating Factors:

•   Only applications or utilities that were created using the 
  Interix SDK and specifically that use the Sun RPC library, 
  would be affected by these vulnerabilities. 
  

•   If an administrator or developer has only installed the 
  Interix SDK but has not actually created applications with
  the SDK that use the Sun RPC library, the systems where the 
  SDK was installed would not be vulnerable. 
  

Risk Rating:

• Internet systems: Moderate
• Intranet systems: Moderate
• Client systems: Moderate

Patch Availability:

• A patch is available to fix this vulnerability. Please read the
  Security Bulletin at
  http://www.microsoft.com/technet/security/bulletin/ms02-057.asp
  for information on obtaining this patch.

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