[FDSA] Sort - Critical Format String Vulnerability

["Fredrick Diggle" <fdiggle () gmail com>]

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                             Fredrick Diggle Security Advisory

Application: Sort
Versions: 5.1.2600.0 verified to be vulnerable
Platforms: Microsoft Windows (All Versions)
Bugs: Format String Vulnerability
Severity: Quite High
Date: 17 Jan 2008
Credit: Fredrick Diggle

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1) Introduction
2) Bugs
3) Proof of Concept
4) Fix

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===============
1) Introduction
===============

Fredrick Diggle Security Services is probably the best application
security researchers on the scene this month. They have identified
several hundred thousand vulnerabilities this week for which Priv8
0dayz have been developed. Fredrick Diggle Security Team periodically
releases several of these vulnerabilities to the community at large
(Pre Vendor Release!!!!). Fred Diggle would like to ensure that you
understand this is 0DAY!!!. The vendors are completely unaware of this
vulnerabilities.

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2) Bug
=======

Sort is a utility which is built into all current versions of
Microsoft Windows. Sort.exe contains a highly exploitable format
string vulnerability in the Filename command line parameter. The
following dump shows the vulnerability in the sort.exe code:

.text:0100128F                 lea     eax, [ebp+in_str]    ; input string
.text:01001295                 push    eax                      ; format param
.text:01001296                 mov     eax, ds:_iob
.text:0100129B                 add     eax, 40h
.text:0100129E                 push    eax                      ; output
.text:0100129F                 call    ds:fprintf                 ; KABLAM!

The following output shows a manafestation of this vulnerability:

C:\>sort AAAA%x.%x.%x.%x
AAAA7c812f39.0.0.41414141The system cannot find the file specified.

This vulnerability can be trivially exploited to execute arbitrary
code on the computer machine.

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3) Proof of Concept
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The following command line will use sort.exe to execute the windows calculator.

C:\>sort CALC.EXE%x%x%x%n | calc

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4) Fix
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Sort should be rewritten to use a third argument to fprintf. The
second argument should be a format string similar to "%s" instead of
the input string.

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