[Snort-users] file_inspect holds blocked files into its memory until snort stops

Joel Esler (jesler) jesler at cisco.com
Thu Sep 7 07:23:49 EDT 2017

The first question I would ask is, why are you not using the most up to date version of Snort.  If this issue was fixed in a later version, that may clear it up right away.

Joel Esler | Talos: Manager | jesler at cisco.com<mailto:jesler at cisco.com>

On Sep 7, 2017, at 1:56 AM, Berkay Koyutürk <berkay.koyuturk at labrisnetworks.com<mailto:berkay.koyuturk at labrisnetworks.com>> wrote:

Hi everybody,

As title says above I have a problem with file_inspect preprocessor. I am running snort with inline mod with file configurations below:

#file config

config file: \
  file_type_depth 0, \
  file_signature_depth 0, \
  file_capture_memcap 1000, \
  file_capture_max 4294967295, \
  file_block_timeout 1, \
  file_capture_min 0

#file_inspect preprocessor

preprocessor file_inspect: \
   signature, \
   capture_disk /root/captured_files 1024, \
   capture_queue_size 5000, \
   blacklist sha_blacklist, \
   greylist sha_greylist


alert ( msg: “File signature “; sid: 1; gid: 147; rev: 1; metadata: rule-type preproc; )

With these configurations I can successfully block downloading files if its sha256 sum is in sha_blacklist file. My problem is , while snort running it keeps holding this files on its memory and after a while for example 33 files with 10MB each, it stops blocking files even cant see them anymore. My snort exit stats is below:

 Total file type callbacks:            0
 Total file signature callbacks:       33
 Total files would saved to disk:      33
 Total files saved to disk:            0
 Total file data saved to disk:        0         bytes
 Total files duplicated:               33
 Total files reserving failed:         0
 Total file capture min:               0
 Total file capture max:               0
 Total file capture memcap:            0
 Total files reading failed:           0
 Total file agent memcap failures:     0
 Total files sent:                     0
 Total file data sent:                 0
 Total file transfer failures:         0
File type stats:
        Type              Download   (Bytes)      Upload (Bytes)
           Total          0          0            0 0

File signature stats:
        Type              Download   Upload
Undecided file type, continue...(  0)          33 0
           Total          33         0

File type verdicts:
       UNKNOWN:           0
           LOG:           0
          STOP:           0
         BLOCK:           0
        REJECT:           0
       PENDING:           0
  STOP CAPTURE:           0
         Total:           0

File signature verdicts:
       UNKNOWN:           0
           LOG:           0
          STOP:           0
         BLOCK:           33
        REJECT:           0
       PENDING:           0
  STOP CAPTURE:           0
         Total:           33

Total files processed:             33
Total files data processed:        346030080 bytes
Total files buffered:              33
Total files released:              33
Total files freed:                 0
Total files captured:              33
Total files within one packet:     0
Total buffers allocated:           10560
Total buffers freed:               0
Total buffers released:            10560
Maximum file buffers used:         379
Total buffers free errors:         0
Total buffers release errors:      0
Total memcap failures:             0
Total memcap failures at reserve:  0
Total reserve failures:            0
Total file capture size min:       0
Total file capture size max:       0
Total capture max before reserve:  0
Total file signature max:          0
Maximum buffers can allocate:      31976
Number of buffers in use:          0
Number of buffers in free list:    21416
Number of buffers in release list: 10560

With this stat above I downloaded 52 files and first 36 are blocked but after that snort didn't even see them .I am using snort version with daq inline mod. Am I forgetting some sort of configuration or is it a bug? Thanks for help

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