Re: corrupted files reported by sophie & SAVI

Markus Stumpf <[email protected]>
Newsgroups gmane.comp.security.virus.vtools
Organization SpaceNet AG, Muenchen, Germany
Message-ID <[email protected]>
On Sat, Jan 24, 2004 at 10:20:50AM +0100, Maciej Uhlig wrote:
> what heuristic does Sophos apply to find 11-byte ASCII text file needs
> decoding and
> report it as 'corrupted'???

A different ;-)
But "file" also reports false guesses often enough.

> these files are reported by sweep as virus free. you see, sweep is a black
> box.
> it gets from SAVI: 'file corrupted' but it puts to the user 'no viruses were
> discovered', I suppose.
> which is true.... but sophie is more precise...

No, sweep also reports "file corrupted" if it thinks the file is
corrupted. It probably only uses a different set of options.

> > With the fix to correctly set the type for the Grp* options
> > and with setting "ZipUseChd: 1" and "limit_classif: 5000", nearly
> > all my problems with warning about corrupt files went away.
> 
> so I second a request from Ed: please let us see your /etc/sophie.savi.

I have atteched it to this mail.

> are you sure the file is being unpacked/decoded at all when ZipUseChd option
> is set :-)?
> maybe it is skipped? we don't know what this undocumented option does in
> fact. we only
> know it supressess the number of reports about corrupted files.

I had different ZIP files. Some of the were fine some reported
"corrupt file". Even the latter where decodable perfectly by unzip.
Repacking the contents revealed a slightly different ZIP that could be
scanned without problems. Maybe different decoders produce different
ZIP compressed files. zipinfo reports for the "corrupt file":
    -rw----     2.0 fat   135858 bl defN 22-Jan-04 17:10 BF001326.dbf
    1 file, 135858 bytes uncompressed, 9379 bytes compressed:  93.1%
The "bl" flags mean
    b = binary
    l = there is an extended local header but no extra field
Maybe - *speculating* - Chd means something like "check header" and
without that flag the scanner reports type "l" ZIP archives as being
corrupt.
I have no idea what that type "l" really means.

	\Maex

-- 
SpaceNet AG            | Joseph-Dollinger-Bogen 14 | Fon: +49 (89) 32356-0
Research & Development |       D-80807 Muenchen    | Fax: +49 (89) 32356-299
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sophie.savi (text/plain, 9.7 KB)
#############################################################################
#                                                                           #
# Meaningful descriptions were taken from SAVI Developer Toolkit Supplement #
# document.                                                                 #
#                                                                           #
# Meaningless descriptions were, of course, added by me :)                  #
#                                                                           #
#############################################################################

#############################################################################
#                                                                           #
# Group options automatically activate/deactivate all options that belong   #
# to the group. You'll have to figure out what belongs where, sorry :)      #
#                                                                           #
# If you want to deactivate certain feature from a group, just set it to 0  #
# but make sure group definitions do remain at the top of this file         #
#############################################################################

# Executable files
GrpExecutable: 1

# All archive and compressed archive file formats (e.g. ZIP, UUE, etc)
GrpArchiveUnpack: 1

# File formats that contain an executable stub that automatically decompresses
# the body of the file
GrpSelfExtract: 1

# File formats commonly in use on the internet
GrpInternet: 1

# Microsoft Office file formats
GrpMSOffice: 1

# File formats that do not fall into any of the above categories
GrpMisc: 1

# Any option that is part of a group is also included in this group
# (NOTE: I have no idea what this really means :)
GrpSuper: 0

# Enables or disables disinfection of all files for which disinfection is
# supported
GrpDisinfect: 0

#########################
#                       #
# Configuration options #
#                       #
#########################

# Controls handling of Macintosh resounce and data fork files (on platforms
# where these are supported). Settings are:
#
# 0 = Disabled
# 1 = SOPHOS_DOS_FILES (enable scanning for Mac viruses)
# 2 = SOPHOS_MAC_FILES (scan data fork files for DOS viruses)
# 3 = SOPHOS_DOS_AND_MAC_FILES (mix :)
#NamespaceSupport: 0

# Enables full sweeping, which performs extensive fixed pattern matching as
# well as the standard intelligent virus search. Turning on this option
# might have severe performance implications.
FullSweep: 1

Base64: 1

# Controls the ability to scan inside supported types of dynamically
# compressed executables.
DynamicDecompression: 1

# Enables a fallback mechanism that has been deployed in the past when new
# file structures are encountered. Sophos recommends that you keep this
# option turned off.
#FullMacroSweep: 0

# Enables the intelligent scanning of OLE2 (Microsoft Office) format
# documents. Sophos recommends that this option should be turned on.
OLE2Handling: 1

# Microsoft Office documents that contain executable macros will usually have
# a single bit in the file header set to 1 to indicate the presence of
# executable code. Under normal circumstances macros contained in a file that
# does not have this bit set are not able to execute. If this option is
# turned off, the Virus Engine will scan only files with this template bit
# set to 1. Sophos recommends that you keep this option turned on.
IgnoreTemplateBit: 1

# This option enables the scanning of Microsoft Visual Basic for Applications
# embedded in supported file types, like Office and Visio documents.
VBA3Handling: 1

# This option enables the scanning of Microsoft Visual Basic for Applications
# embedded in supported file types, like Office and Visio documents.
VBA5Handling: 1

# Password-protected Office 95 documents are encrypted with a very simple
# algorithm. Enabling this option causes the virus engine to break this
# encryption to search for viruses.
OF95DecryptHandling: 1

# Enables checking for files embedded in Mirosoft Help files.
HelpHandling: 1

# Decompresses the text part of a VBA5 project before scanning. This area is
# often corrupted, but can help positive identification of some viruses.
DecompressVBA5: 1

# Enables the 16-bit x86 emulation engine, which assists in the detection of
# polymorphic executable file viruses. Sophos recommends this option should be
# turned on.
Emulation: 1

# Enables the intelligent scanning of Win32/PE format files. This is the
# standard format for Windows executable binaries such as .exe  and .dll.
PEHandling: 1

# Enables scanning of Excel formulas for known formula viruses. Formulas
# occupy cells on the worksheet and should not be confused with macros.
ExcelFormulaHandling: 1

# Enables the scanning of macros in PowerPoint presentations.
PowerPointMacroHandling: 1

# Enables the scanning of files embedded within PowerPoint presentations.
PowerPointEmbeddedHandling: 1

# Enables the scanning of VBA macros in Microsoft Project.
ProjectHandling: 1

# Enables scanning inside ZIP archives.
ZipDecompression: 1
ZipUseChd: 1

# Enables decompression of Arj archives.
ArjDecompression: 1

# Enables decompression of RAR archives.
RarDecompression: 1

# Enables the virus engine to decode EEUncoded files. The UUEncode portion
# must start within the first 4k of the document.
UueDecompression: 1

# Enables decompression of Gzipped archives.
GZipDecompression: 1

# Enables scanning inside UNIX tar archives.
TarDecompression: 1

# Enables decompression of Cmz archives.
CmzDecompression: 1

# Contols the ability to extract files from BinHex archives.
HqxDecompression: 1

# Controls the ability to look inside MacBinary archives.
MbinDecompression: 1

# Controls SAVI's ability to scan inside certain types of container file.
# Sophos recommends that this options should be turned on.
LoopBackEnabled: 1

# Contols the maximum number of times the engine will recurse into archives
# when they are found (e.g. when a zip file is compressed within another zip
# file). The maximum value is 100, but SAVI internally has some extra levels
# of recursion to cover internal data streams found within some file types.
MaxRecursionDepth: 16

# Enables decompression of Lha archives.
Lha: 1

# Enables the virus engine to search in supported types of self-extracting
# archive.
SfxArchives: 1

# Enables decoding of files encoded with the Microsoft TNEF format, used by
# some mail client applications.
TnefAttachmentHandling: 1

# Controls the ability to scan inside files compressed with the Microsoft
# compression utility.
MSCompress: 1

# Enables decompression of Microsoft Cabinet files (.cab) (Partial files at
# the beginning and end of multi-part cabinet files will not be fully
# scanned
#MSCabinet: 1

# Applies to Microsoft Office and other OLE2 format files. When this option is
# enabled, calls to DisinfectFile() all macros present in the document are
# deleted, regardless of whether or not they are viral.
#DeleteAllMacros: 0

# Enables the scanning of encoded VBScript files.
Vbe: 1

# Some executable file viruses can be removed from files fairly safely. This
# option enables that process. Sophos recommends that infected executables are
# replaced from the original installation disks as soon as possible.
#ExecFileDisinfection: 0

# Enables the scanning of Microsoft Visio files.
VisioFileHandling: 1

# Enables decoding and scanning inside a MIME encoded message block.
Mime: 0

# Enables the detection of macro viruses within Microsoft Office documents
# saved in ActiveMime document format.
ActiveMimeHandling: 1

# Causes the entire project containing any viral macros to be removed during
# disinfection.
#DelVBA5Project: 0

# Enables the handling of scrap objects that are used in the transfer of data
# between certain applications.
ScrapObjectHandling: 1

# Deals with another type of data within Office documents.
SrpStreamHandling: 1

# Controls the ability of the engine to understand Microsoft Office 2001
# files (Macintosh only)
Office2001Handling: 1

# Enables scanning inside UPX-compressed self-extracting executable archives.
Upx: 1

# FIXME: No idea what this is used for
#Mac: 0

# FIXME: No idea what this is used for
#SafeMacDfHandling: 0

# Enables the scanning of Palm Pilot format files (.prc).
PalmPilotHandling: 1

# Controls the PDF file interpretation module.
Pdf: 1

# Enables scanning for objects that may be embedded inside Rich Text  FOrmat
# files.
Rtf: 1

# Controls the module that optimises scanning in HTML files.
Html: 1

# Controls the module that interprets ELF binary files. This format is used
# for many Linux and FreeBSD executable files.
Elf: 1

# Enables the scanning of WordBasic.
WordB: 1

# Enables scanning of files contained within Outlook Express mailboxes.
OutlookExpress: 1

# FIXME: Well, I have some idea...
Java: 1

# FIXME: Well, I have some idea...
Access: 1

# FIXME: No idea what this is used for
#AppleSingle: 0

# FIXME: No idea what this is used for
VbFiltering: 1

#######################################################
#                                                     #
# DO NO SET/USE ANY OF THESE CONFIGURATION OPTIONS!!! #
#                                                     #
#######################################################

# The passed string defines the full path name of the directory in which the
# main virus data file is located. The name should not have a trailing 
# directory separator character.
#VirusDataDir: 

# The passed string defines the name of the virus data file. This name should
# not include a directory component (this is defined by the VirusDataDir
# setting) or a file extension. For example, if the main virus data file name
# is vdl.dat then this string should be passed as vdl.
#VirusDataName: 

# The passed string defines the full path name of the directory in which SAVI
# should search for IDE files.
IdeDir:
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