.. _run_security:
Security first
==============
If you are the only person involved in running Varnish, or if all
the people involved are trusted to the same degree, you can skip
this chapter. We have protected Varnish as well as we can from
anything which can come in through an HTTP socket.
If parts of your web infrastructure are outsourced or otherwise
partitioned along administrative lines, you need to think about
security.
Varnish provides four levels of authority, roughly related to
how and where control comes into Varnish:
* The command line arguments,
* The CLI interface,
* VCL programs, and
* HTTP requests.
Command line arguments
----------------------
The top level security decisions is decided and defined when starting
Varnish in the form of command line arguments, we use this strategy
in order to make them invulnerable to subsequent manipulation.
The important decisions to make are:
#. Who should have access to the Command Line Interface?
#. Which parameters can they change?
#. Will inline-C code be allowed?
#. If/how VMODs will be restricted?
#. How child processes will be jailed?
CLI interface access
^^^^^^^^^^^^^^^^^^^^
The command line interface can be accessed in three ways.
`varnishd` can be told to listen and offer CLI connections
on a TCP socket. You can bind the socket to pretty
much anything the kernel will accept::
-T 127.0.0.1:631
-T localhost:9999
-T 192.168.1.1:34
-T '[fe80::1]:8082'
The default is ``-T localhost:0`` which will pick a random
port number, which `varnishadm(8)` can learn from the shared
memory.
By using a "localhost" address, you restrict CLI access
to the local machine.
You can also bind the CLI port to an IP address reachable across
the net, and let other machines connect directly.
This gives you no secrecy, i.e. the CLI commands will
go across the network as ASCII text with no encryption, but
the -S/PSK authentication requires the remote end to know
the shared secret.
Alternatively you can bind the CLI port to a 'localhost' address,
and give remote users access via a secure connection to the local
machine, using ssh/VPN or similar.
If you use `ssh` you can restrict which commands each user can execute
to just `varnishadm`, or even use a wrapper scripts around `varnishadm`
to allow specific CLI commands.
It is also possible to configure `varnishd` for "reverse mode", using
the '-M' argument. In that case `varnishd` will attempt to open a
TCP connection to the specified address, and initiate a CLI connection
to your central Varnish management facility.
.. XXX:Maybe a sample command here with a brief explanation? benc
The connection in this case is also without encryption, but
the remote end must still authenticate using -S/PSK.
Finally, if you run varnishd with the '-d' option, you get a CLI
command on stdin/stdout, but since you started the process, it
would be hard to prevent you getting CLI access, wouldn't it ?
CLI interface authentication
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
By default the CLI interface is protected with a simple, yet powerful
"Pre Shared Key" authentication method, which do not provide secrecy
(ie: The CLI commands and responses are not encrypted).
The way -S/PSK works is really simple: During startup a file is
created with a random content and the file is only accessible to
the user who started `varnishd` (or the superuser).
To authenticate and use a CLI connection, you need to know the
contents of that file, in order to answer the cryptographic
challenge `varnishd` issues, see :ref:`ref_psk_auth`.
`varnishadm` uses all of this to restrict access, it will only function,
provided it can read the secret file.
If you want to allow other users, local or remote, to be able to access
CLI connections, you must create your own secret file and make it possible
for (only!) these users to read it.
A good way to create the secret file is::
dd if=/dev/random of=/etc/varnish_secret count=1
When you start `varnishd`, you specify the filename with '-S', and
it goes without saying that the `varnishd` master process needs
to be able to read the file too.
You can change the contents of the secret file while `varnishd`
runs, it is read every time a CLI connection is authenticated.
On the local system, `varnishadm` can retrieve the filename from
shared memory, but on remote systems, you need to give `varnishadm`
a copy of the secret file, with the -S argument.
If you want to disable -S/PSK authentication, specify '-S' with
an empty argument to varnishd::
varnishd [...] -S "" [...]
Parameters
^^^^^^^^^^
Parameters can be set from the command line, and made "read-only"
(using '-r') so they cannot subsequently be modified from the CLI
interface.
Pretty much any parameter can be used to totally mess up your
HTTP service, but a few can do more damage than others:
:ref:`ref_param_cc_command`
Execute arbitrary programs
:ref:`ref_param_vcc_allow_inline_c`
Allow inline C in VCL, which would any C code from VCL to be executed by Varnish.
Furthermore you may want to look at and lock down:
:ref:`ref_param_syslog_cli_traffic`
Log all CLI commands to `syslog(8)`, so you know what goes on.
:ref:`ref_param_vcc_unsafe_path`
Restrict VCL/VMODs to :ref:`ref_param_vcl_path` and :ref:`ref_param_vmod_path`
:ref:`ref_param_vmod_path`
The directory (or colon separated list of directories) where
Varnish will look for modules. This could potentially be
used to load rogue modules into Varnish.
The CLI interface
-----------------
The CLI interface in Varnish is very powerful, if you have
access to the CLI interface, you can do almost anything to
the Varnish process.
As described above, some of the damage can be limited by restricting
certain parameters, but that will only protect the local filesystem,
and operating system, it will not protect your HTTP service.
We do not currently have a way to restrict specific CLI commands
to specific CLI connections. One way to get such an effect is to
"wrap" all CLI access in pre-approved scripts which use `varnishadm(1)`
to submit the sanitized CLI commands, and restrict a remote user
to only those scripts, for instance using sshd(8)'s configuration.
VCL programs
------------
There are two "dangerous" mechanisms available in VCL code: VMODs
and inline-C.
Both of these mechanisms allow execution of arbitrary code and will
thus allow a person to get access to the machine, with the
privileges of the child process.
If `varnishd` is started as root/superuser, we sandbox the child
process, using whatever facilities are available on the operating
system, but if `varnishd` is not started as root/superuser, this is
not possible. No, don't ask me why you have to be superuser to
lower the privilege of a child process...
Inline-C is disabled by default starting with Varnish version 4, so unless
you enable it, you don't have to worry about it.
The parameters mentioned above can restrict the loading of VMODs to only
be loaded from a designated directory, restricting VCL wranglers to a
pre-approved subset of VMODs.
If you do that, we are confident that your local system cannot be compromised
from VCL code.
HTTP requests
-------------
We have gone to great lengths to make Varnish resistant to anything
coming in through the socket where HTTP requests are received, and
you should, generally speaking, not need to protect it any further.
The caveat is that since VCL is a programming language which lets you
decide exactly what to do with HTTP requests, you can also decide
to do stupid and potentially dangerous things with them, including opening yourself up
to various kinds of attacks and subversive activities.
If you have "administrative" HTTP requests, for instance PURGE
requests, we strongly recommend that you restrict them to trusted
IP numbers/nets using VCL's :ref:`vcl_syntax_acl`.
Henceforth, whatever our philosopher says about Matter will apply to extension and to extension alone. It cannot be apprehended by sight, nor by hearing, nor by smell, nor by taste, for it is neither colour, nor sound, nor odour, nor juice. Neither can it be touched, for it is not a body, but it becomes corporeal on being blended with sensible qualities. And, in a later essay, he describes it as receiving all things and letting them depart again without retaining the slightest trace of their presence.483 Why then, it may be asked, if Plotinus meant extension, could he not say so at once, and save us all this trouble in hunting out his meaning? There were very good reasons why he should not. In the first place, he wished to express himself, so far as possible, in Aristotelian phraseology, and this was incompatible with the reduction of Matter to extension. In the next place, the idea of an infinite void had been already appropriated by the Epicureans, to whose system he was bitterly opposed. And, finally, the extension of ordinary327 experience had not the absolute generality which was needed in order to bring Matter into relation with that ultimate abstraction whence, like everything else, it has now to be derived. That the millionaire was genuine, ¡°in person and not a caricature,¡± as Dick put it, was evident. Both the nurse, his relative, and his wife, were chatting with him as Jeff delivered the heavy packed ball made up of the gum. 233 "I guess not," said Landor, tolerantly, as he turned[Pg 106] his horse over to his orderly; "but, anyway," he added to Ellton, "we had a picnic¡ªof a sort." Si, unable to think of anything better, went with him. The train had stopped on a switch, and seemed likely to rust fast to the rails, from the way other trains were going by in both directions. The bridge gang, under charge of a burly, red-faced young Englishman, was in the rear car, with their tools, equipments, bedding and cooking utensils. THE DEACON HAS SOME EXPERIENCES WITH THE QUADRUPED. "You are not within a mile of the truth. I know it. Look here: I believe that is Gen. Rosecrans's own cow. She's gone, and I got an order to look around for her. I've never seen her, but from the description given me I believe that's she. Who brought her here?" "Deacon, these brothers and sisters who have come here with me to-night are, like myself, deeply interested in the moral condition of the army, where we all have sons or kinsmen. Now, can't you sit right there and tell us of your observations and experiences, as a Christian man and father, from day to day, of every day that you were down there? Tell us everything, just as it happened each day, that we may be able to judge for ourselves." HAS AN ENCOUNTER WITH THE PROVOST-MARSHAL. "Wonder which one o' them is the 200th Injianny's?" said Si to Shorty. "And your mother, and Harry?" The daughter must be the girl who was talking to him now. She sat on a little stool by the fire, and had brought out some sewing. "Over at Grandturzel¡ªcan't see wot's burning from here. Git buckets and come!" These things, however, gave little concern to the worthy who commanded the Kentish division. Tyler, though an excellent blacksmith, possessed few of the qualities requisite for forming a good general. Provided there was no very sensible diminution in the number of his followers, he cared not a straw for the score or two who, after quarrelling, or perhaps fighting, withdrew in such disgust that they vowed rather to pay the full tax for ever than submit to the insolence of the rebels. One man could fight as well as another, reasoned he; and, provided he was obeyed, what mattered it by whom. Dick went and Tom came¡ªit was sure to be all one in the end. But this burst of indignation soon passed away, and upon the suggestion of the prudent Sir Robert Hailes, he sent an evasive answer, with a command that the Commons should attend him at Windsor on the Sunday following. That it was a stratagem to gain entrance to the Tower, was the opinion of several, but, after much discussion, it was decided that the man should be admitted, and that the monk should be exhibited merely to intimidate the rebels, until the result of this promised communication should be known. HoMEŮͬÐÔÁµcbcb
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