Palo Alto Networks Knowledgebase: SMB Traffic is Blocked and the Windows Explorer Window Hangs While Accessing a Shared Folder

SMB Traffic is Blocked and the Windows Explorer Window Hangs While Accessing a Shared Folder

Created On 02/07/19 23:44 PM - Last Updated 02/07/19 23:44 PM


Server Message Block (SMB) traffic is blocked and the Windows Explorer window hangs while accessing a shared folder.



This can happen when there is a file blocking profile, with a block action used in a Security Rule that is matched by that session.



Under Security Policies > Actions, if a session goes through the Palo Alto Networks firewall and matches a specific allow policy, according to the defined criteria, the action defined in the policy will be taken.

In the example below, the Security Policy Rule that is matched is "allow_all", which has a profile for file blocking.

Screen Shot 2014-08-20 at 4.01.20 PM.png


The File Blocking Profile is blocking all PE files (which includes .exe, .msi), any file in that session that matches the file type will take the session into the discard state.

Screen Shot 2014-08-20 at 4.01.56 PM.png


As soon as a user opens the shared folder that has .exe file in it, that session opening will go into discard state and no other files will be able to move between the machines.


> show session all filter destination



ID          Application    State   Type Flag  Src[Sport]/Zone/Proto (translated IP[Port])

Vsys                                          Dst[Dport]/Zone (translated IP[Port])


152568       ms-ds-smb      DISCARD FLOW  NS[49158]/Trust-L3/6  ([32047])

vsys1                                [445]/Untrust-L3  ([445])



See the following example, session is set to discard state by security policy check:

> show session id 152568


Session          152568


        c2s flow:

                source: [Trust-L3]


                proto:       6

                sport:       49158           dport:      445

                state:       INIT            type:       FLOW

                src user:    unknown

                dst user:    unknown


        s2c flow:

                source: [Untrust-L3]


                proto:       6

                sport:       445             dport:      32047

                state:       INIT            type:       FLOW

                src user:    unknown

                dst user:    unknown


        start time                    : Thu Apr 17 17:12:56 2014

        timeout                       : 90 sec

        total byte count(c2s)         : 44292

        total byte count(s2c)         : 50073

        layer7 packet count(c2s)      : 182

        layer7 packet count(s2c)      : 176

        vsys                          : vsys1

        application                   : ms-ds-smb 

        rule                          : allow_all

        session to be logged at end   : True

        session in session ager       : False

        session synced from HA peer   : False

        address/port translation      : source + destination

        nat-rule                      : NAT_all_inside_to_out(vsys1)

        layer7 processing             : completed

        URL filtering enabled         : True

        URL category                  : any

        session via syn-cookies       : False

        session terminated on host    : False

        session traverses tunnel      : False

        captive portal session        : False

        ingress interface             : ethernet1/2

        egress interface              : ethernet1/1

        session QoS rule              : N/A (class 4)

        tracker stage firewall        : mitigation block cont url


As soon as the folder is opened, the SMB session will go into the discard state. If the same folder has .txt files, and if trying to copy them, it will fail because the SMB session is already discarded. This is going to happen even if there is no blocking policy for the .txt files.

The user will experience this as their Windows Explorer application hangs and does not return any results after the share folder was opened.


As shown below, the global counters confirms that information too:

> show counter global filter packet-filter yes delta yes


Global counters:

Elapsed time since last sampling: 58.678 seconds


name                                   value     rate severity  category  aspect    description


pkt_recv                                1511       25 info      packet    pktproc   Packets received

pkt_sent                                 349        5 info      packet    pktproc   Packets transmitted

session_allocated                          2        0 info      session   resource  Sessions allocated

session_installed                          2        0 info      session   resource  Sessions installed

session_discard                            4        0 info      session   resource  Session set to discard by security policy check

flow_fwd_mtu_exceeded                     21        0 info      flow      forward   Packets lengths exceeded MTU

flow_ipfrag_frag                          42        0 info      flow      ipfrag    IP fragments transmitted

flow_host_pkt_xmt                       1248       21 info      flow      mgmt      Packets transmitted to control plane

flow_host_vardata_rate_limit_ok         1227       20 info      flow      mgmt      Host vardata not sent: rate limit ok

appid_ident_by_dport                       1        0 info      appid     pktproc   Application identified by L4 dport

appid_proc                                 2        0 info      appid     pktproc   The number of packets processed by Application identification

appid_use_dfa_1                            2        0 info      appid     pktproc   The number of packets using the second DFA table

appid_skip_terminal                        2        0 info      appid     pktproc   The dfa result is terminal

nat_dynamic_port_xlat                      2        0 info      nat       resource  The total number of dynamic_ip_port NAT translate called

dfa_sw                                   326        5 info      dfa       pktproc   The total number of dfa match using software

ctd_run_pattern_match_failure              2        0 info      ctd       pktproc   Run pattern match failure

aho_sw                                   507        8 info      aho       pktproc   The total usage of software for AHO

ctd_appid_reassign                         5        0 info      ctd       pktproc   appid was changed

ctd_pkt_slowpath                         318        5 info      ctd       pktproc   Packets processed by slowpath

ctd_detector_discard                       2        0 info      ctd       pktproc   session discarded by detector

log_pkt_diag_us                        23585      401 info      log       system    Time (us) spend on writing packet-diag logs


Total counters shown: 21




This is expected behavior because of the nature of the SMB. If there is a Security Rule with a block profile attached to it for SMB sessions, it is best to not mix file types that are supposed to be blocked, with a policy with allowed files.


owner: ialeksov

  • Print
  • Copy Link

Choose Language