RE: [Full-Disclosure] Winrar doesn't determine the actual size of compressed files

From: Rainer Gerhards (rgerhards_at_hq.adiscon.com)
Date: 09/09/03

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    To: <door_hUNT3R@blackcodemail.com>, <full-disclosure@lists.netsys.com>
Date: Tue, 9 Sep 2003 14:49:31 +0200

    tested with 3.20 - can't reproduce. It says "file is corrupt", I press "close" - nothing happened....

    Rainer

    > -----Original Message-----
    > From: Bipin Gautam [mailto:door_hUNT3R@blackcodemail.com]
    > Sent: Tuesday, September 09, 2003 1:02 PM
    > To: full-disclosure@lists.netsys.com
    > Subject: [Full-Disclosure] Winrar doesn't determine the
    > actual size of compressed files
    >
    >
    > ---[ about WinRAR]---
    > Winrar (http://www.rarsoft.com/) is one of the most popular
    > file compression utilities for Windows.
    >
    > --[summary]---
    > Winrar incorrectly determines the actual size of compressed
    > files saved in .rar format by reading it's header information.
    >
    > --[details]--
    > Recently we managed to devise a technique to spoof the header
    > and creating a valid CRC checksum. Later we found that Winrar
    > only depends on it's header information and CRC check sum to
    > determine the size and integrity of .rar files. Before
    > uncompressing .rar files, Winrar pre-allocates space
    > according to the actual file size specified in the header to
    > avoid fragmentation.But pre-allocation occurs without
    > checking the available hdd space. Then it goes extracting,
    > even if the hdd size is less than the size of the files.We
    > did a test by extracting 1GB files in a hdd with 700MB free space.
    >
    > Surprisingly, we later discover that even in detecting of
    > header corruption WinRAR doesn't enforce to avoid extraction
    > process. this lead WinRAR to believe that the actual size is
    > correct .We managed to exploit this and create a proof of
    > concept to demonstrate this problem by changing the actual
    > file size in it's header. When it starts extracting it
    > doesn't find any valid data in the archive and on the basis
    > of it's header it attempts to extract 1 gigabyte of data and
    > simply goes on writing "0x00" filling up valuable hdd space.
    >
    > --[Proof of concept]--
    > The proof of concept is a valid .rar file which is just 100
    > bytes but it's header has been forged to fool Winrar into
    > thinking that it's a 1 gigabyte file by forging it's header
    > and creating a valid CRC checksum. All versions of Winrar
    > (upto 3.20 - latest version till date) seem to be vulnerable.
    >
    > The proof of concept of .rar file can be obtained from the
    > following URL: http://www.geocities.com/visitbipin/test123.zip
    > If you extract the file Winrar will try to extract this 100
    > bytes .rar file trusting the information in it's header but
    > not on the basis of it's data integrity.
    >
    > --[Background Information]--
    > This bug was originally discovered by hUNT3R, a member of 01
    > Security Sumbission. The vendor was notified via email.
    > Further discussion took place in 01 Security Sumbission's
    > forum with the developer of Winrar (Eugene Roshal) :
    > URL: http://www.ysgnet.com/phorum/read.php?f=1&i=341&t=324#reply_341
    >
    > ---[about 01 security submission]---
    > 01s.s is a small group having experience as security
    > specialists, programmers and system administrators
    > http://www.ysgnet.com/hn.
    >
    >
    >
    > | .oÛ_Oo.h»UNTER.oO_Ûo. |
    > § !¹007Õ°¿ÑïÞÎß°Õæ9*½¹! ‡
    >
    > _____________________________________________________________
    > Secure mail ---> http://www.blackcode.com
    >
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    > Charter: http://lists.netsys.com/full-disclosure-charter.html
    >

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