Snort mailing list archives
Re: File magic rules for 2.9.6, what options are required?
From: Joshua Kinard <kumba () gentoo org>
Date: Fri, 27 Dec 2013 11:13:05 -0500
On 12/26/2013 10:16 PM, Joel Esler (jesler) wrote:
Thanks Joshua, one of the devels will get back to you.
Couple of additional questions/ideas: - 'content' keyword should be a quoted string and optionally allow ASCII. I can see why the initial draft is to allow hexadecimal only, but one finds that a lot of file magics use printable ASCII. I.e., "%PDF-1." for PDF, "ELF" for Linux/Unix ELF executables, classic "MZ" for PE executables. - This specification doesn't appear to handle cases like PE executables, where sometimes checking for "MZ" alone is not enough. You'll still want to use a byte_jump to reach the start of the PE header to really verify that you're dealing with a PE executable. But I understand this is a first cut of this feature, so it'll probably get beefed up in the future. That and a flowbit setter rule for PE executables is trivial enough. - 'category' appears to be an unquoted string, but the example documentation suggests it can, and cannot, accept spaces. The second sentence implies no whitespace, while the third sentence implies it does: category: defines the categories of file type. Name should be limited to any alphanumeric string including periods, dashes, and underscores. Categories can be Executables, PDF files, FLASH files, Office Documents, Archive, Graphics, Multimedia etc. I'd suggest making category take a quoted string if whitespace is going to be allowed. This'll avoid easily-made syntax errors when people start writing these things. - ver: unquoted string, right? The source suggests such. Thanks!, --J
Sent from my iPhone.On Dec 26, 2013, at 15:45, "Joshua Kinard" <kumba () gentoo org> wrote: Doing a quick glance at the new file magic "rules" that one can specify in 2.9.6 RC, I am not directly seeing a definition of which of the options are required and which aren't. So far, it looks like I can write this: file type:FOO; And ~/bin/snort -c local.rules -T parses w/o error. Logically, my guess is that the following option keywords are going to be required for a 'file' definition to work correctly: type id msg content With these being optional: ver category group (required only if >1 definition of 'type') offset (assumed 0 if not specified) rev (assumed 1 if not specified) Does this sound about right?
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Current thread:
- File magic rules for 2.9.6, what options are required? Joshua Kinard (Dec 26)
- Re: File magic rules for 2.9.6, what options are required? Joel Esler (jesler) (Dec 26)
- Re: File magic rules for 2.9.6, what options are required? Joshua Kinard (Dec 27)
- Re: File magic rules for 2.9.6, what options are required? Joshua Kinard (Dec 27)
- Re: File magic rules for 2.9.6, what options are required? Joel Esler (jesler) (Dec 27)
- Re: File magic rules for 2.9.6, what options are required? Hui Cao (Dec 27)
- Re: File magic rules for 2.9.6, what options are required? Joshua Kinard (Dec 27)
- Re: File magic rules for 2.9.6, what options are required? Joshua Kinard (Dec 27)
- Re: File magic rules for 2.9.6, what options are required? Victor Roemer (Dec 27)
- Re: File magic rules for 2.9.6, what options are required? Joshua Kinard (Dec 27)
- Re: File magic rules for 2.9.6, what options are required? Joel Esler (jesler) (Dec 26)