Signatures based on container metadata

ClamAV 0.96 allows creating generic signatures matching files stored inside different container types which meet specific conditions. The signature format is:

    VirusName:ContainerType:ContainerSize:FileNameREGEX:
    FileSizeInContainer:FileSizeReal:IsEncrypted:FilePos:
    Res1:Res2[:MinFL[:MaxFL]]

where the corresponding fields are:

  • VirusName: Virus name to be displayed when signature matches.

  • ContainerType: The file type containing the target file. For example:

    • CL_TYPE_ZIP,
    • CL_TYPE_RAR,
    • CL_TYPE_ARJ,
    • CL_TYPE_MSCAB,
    • CL_TYPE_7Z,
    • CL_TYPE_MAIL,
    • CL_TYPE_(POSIX|OLD)_TAR,
    • CL_TYPE_CPIO_(OLD|ODC|NEWC|CRC)

    Use * as a wild card to indicate that container type may be any file type. For a full list of ClamAV file types, see the ClamAV File Types Reference.

  • ContainerSize: size of the container file itself (eg. size of the zip archive) specified in bytes as absolute value or range x-y.

  • FileNameREGEX: regular expression describing name of the target file

  • FileSizeInContainer: usually compressed size; for MAIL, TAR and CPIO == FileSizeReal; specified in bytes as absolute value or range.

  • FileSizeReal: usually uncompressed size; for MAIL, TAR and CPIO == FileSizeInContainer; absolute value or range.

  • IsEncrypted: 1 if the target file is encrypted, 0 if it’s not and * to ignore

  • FilePos: file position in container (counting from 1); absolute value or range.

  • Res1: when ContainerType is CL_TYPE_ZIP or CL_TYPE_RAR this field is treated as a CRC sum of the target file specified in hexadecimal format; for other container types it’s ignored.

  • Res2: not used as of ClamAV 0.96.

The signatures for container files are stored inside .cdb files.