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Does Docker's CAP_NET_ADMIN allow a container to affect the host network, or only it's own?


connecting from docker container to docker hostHow should I configure SELinux when running nginx inside DockerTransparent proxying a single docker container to another docker containerIPTables port redirect with DockerIptables LOG rule inside a network namespaceHow does yum with Red Hat Network Subscription work inside the rhel Docker images?Configure iptables to secure a server running Docker containersSandbox docker containerTwo NICs docker host, fixed container source IP, no connection to second subnetSend received mirrored traffic using iptables to docker application?






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1















I have a docker container running a password authenticated SFTP server (client requirement - I've already lost that battle). In order to mitigate the risk of brute force attacks, I had thought to install iptables and fail2ban within the container. However, to get iptables working this requires that I allow the container NET_ADMIN rights.



I've not been able to find from the Docker documentation whether this allows the container simply to make changes to it's own network, or to amend the host network as well. All I have found is a summary, such as:



Capability Key | Capability Description
---------------|-----------------------
NET_ADMIN | Perform various network-related operations.


Reading the MAN pages linked from the Docker documentation provides a list of the capabilities that this imparts, but of course it's not written in the context of Docker ...



Perform various network-related operations:
- interface configuration;
- administration of IP firewall, masquerading, and accounting
- modify routing tables;
- bind to any address for transparent proxying;
- set type-of-service (TOS)
- clear driver statistics;
- set promiscuous mode;
- enabling multicasting;


... so I'm still unclear whether these abilities are granted at host level, or relates only to the container's network. An alternative strategy I'd come up with was to expose the container's auth.log using a shared volume and have fail2ban run on the host (I'd obviously have to set --iptables=false on the Docker engine), but I preferred the neatness of having no external host dependency and everything within a single container.



Can anyone allay my fears, or provide alternatives?










share|improve this question






















  • Have you ever figured this out?

    – Keeper Hood
    Apr 15 at 15:31

















1















I have a docker container running a password authenticated SFTP server (client requirement - I've already lost that battle). In order to mitigate the risk of brute force attacks, I had thought to install iptables and fail2ban within the container. However, to get iptables working this requires that I allow the container NET_ADMIN rights.



I've not been able to find from the Docker documentation whether this allows the container simply to make changes to it's own network, or to amend the host network as well. All I have found is a summary, such as:



Capability Key | Capability Description
---------------|-----------------------
NET_ADMIN | Perform various network-related operations.


Reading the MAN pages linked from the Docker documentation provides a list of the capabilities that this imparts, but of course it's not written in the context of Docker ...



Perform various network-related operations:
- interface configuration;
- administration of IP firewall, masquerading, and accounting
- modify routing tables;
- bind to any address for transparent proxying;
- set type-of-service (TOS)
- clear driver statistics;
- set promiscuous mode;
- enabling multicasting;


... so I'm still unclear whether these abilities are granted at host level, or relates only to the container's network. An alternative strategy I'd come up with was to expose the container's auth.log using a shared volume and have fail2ban run on the host (I'd obviously have to set --iptables=false on the Docker engine), but I preferred the neatness of having no external host dependency and everything within a single container.



Can anyone allay my fears, or provide alternatives?










share|improve this question






















  • Have you ever figured this out?

    – Keeper Hood
    Apr 15 at 15:31













1












1








1








I have a docker container running a password authenticated SFTP server (client requirement - I've already lost that battle). In order to mitigate the risk of brute force attacks, I had thought to install iptables and fail2ban within the container. However, to get iptables working this requires that I allow the container NET_ADMIN rights.



I've not been able to find from the Docker documentation whether this allows the container simply to make changes to it's own network, or to amend the host network as well. All I have found is a summary, such as:



Capability Key | Capability Description
---------------|-----------------------
NET_ADMIN | Perform various network-related operations.


Reading the MAN pages linked from the Docker documentation provides a list of the capabilities that this imparts, but of course it's not written in the context of Docker ...



Perform various network-related operations:
- interface configuration;
- administration of IP firewall, masquerading, and accounting
- modify routing tables;
- bind to any address for transparent proxying;
- set type-of-service (TOS)
- clear driver statistics;
- set promiscuous mode;
- enabling multicasting;


... so I'm still unclear whether these abilities are granted at host level, or relates only to the container's network. An alternative strategy I'd come up with was to expose the container's auth.log using a shared volume and have fail2ban run on the host (I'd obviously have to set --iptables=false on the Docker engine), but I preferred the neatness of having no external host dependency and everything within a single container.



Can anyone allay my fears, or provide alternatives?










share|improve this question














I have a docker container running a password authenticated SFTP server (client requirement - I've already lost that battle). In order to mitigate the risk of brute force attacks, I had thought to install iptables and fail2ban within the container. However, to get iptables working this requires that I allow the container NET_ADMIN rights.



I've not been able to find from the Docker documentation whether this allows the container simply to make changes to it's own network, or to amend the host network as well. All I have found is a summary, such as:



Capability Key | Capability Description
---------------|-----------------------
NET_ADMIN | Perform various network-related operations.


Reading the MAN pages linked from the Docker documentation provides a list of the capabilities that this imparts, but of course it's not written in the context of Docker ...



Perform various network-related operations:
- interface configuration;
- administration of IP firewall, masquerading, and accounting
- modify routing tables;
- bind to any address for transparent proxying;
- set type-of-service (TOS)
- clear driver statistics;
- set promiscuous mode;
- enabling multicasting;


... so I'm still unclear whether these abilities are granted at host level, or relates only to the container's network. An alternative strategy I'd come up with was to expose the container's auth.log using a shared volume and have fail2ban run on the host (I'd obviously have to set --iptables=false on the Docker engine), but I preferred the neatness of having no external host dependency and everything within a single container.



Can anyone allay my fears, or provide alternatives?







security permissions docker






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Jun 1 '16 at 18:50









DanDan

1266




1266












  • Have you ever figured this out?

    – Keeper Hood
    Apr 15 at 15:31

















  • Have you ever figured this out?

    – Keeper Hood
    Apr 15 at 15:31
















Have you ever figured this out?

– Keeper Hood
Apr 15 at 15:31





Have you ever figured this out?

– Keeper Hood
Apr 15 at 15:31










1 Answer
1






active

oldest

votes


















0














That depends on whether you set --net=host or not:



Or as the man page puts it:




--net="bridge"
Set the Network mode for the container
'bridge': create a network stack on the default Docker bridge
'none': no networking
'container:': reuse another container's network stack
'host': use the Docker host network stack. Note: the host mode gives the container full access to
local system services such as D-bus and is therefore considered
insecure.







share|improve this answer























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    1 Answer
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    active

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    active

    oldest

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    0














    That depends on whether you set --net=host or not:



    Or as the man page puts it:




    --net="bridge"
    Set the Network mode for the container
    'bridge': create a network stack on the default Docker bridge
    'none': no networking
    'container:': reuse another container's network stack
    'host': use the Docker host network stack. Note: the host mode gives the container full access to
    local system services such as D-bus and is therefore considered
    insecure.







    share|improve this answer



























      0














      That depends on whether you set --net=host or not:



      Or as the man page puts it:




      --net="bridge"
      Set the Network mode for the container
      'bridge': create a network stack on the default Docker bridge
      'none': no networking
      'container:': reuse another container's network stack
      'host': use the Docker host network stack. Note: the host mode gives the container full access to
      local system services such as D-bus and is therefore considered
      insecure.







      share|improve this answer

























        0












        0








        0







        That depends on whether you set --net=host or not:



        Or as the man page puts it:




        --net="bridge"
        Set the Network mode for the container
        'bridge': create a network stack on the default Docker bridge
        'none': no networking
        'container:': reuse another container's network stack
        'host': use the Docker host network stack. Note: the host mode gives the container full access to
        local system services such as D-bus and is therefore considered
        insecure.







        share|improve this answer













        That depends on whether you set --net=host or not:



        Or as the man page puts it:




        --net="bridge"
        Set the Network mode for the container
        'bridge': create a network stack on the default Docker bridge
        'none': no networking
        'container:': reuse another container's network stack
        'host': use the Docker host network stack. Note: the host mode gives the container full access to
        local system services such as D-bus and is therefore considered
        insecure.








        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Mar 7 '17 at 20:15









        DejDej

        53




        53



























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