Category: System Administration

Cisco – Converting Access Point from Lightweight to Autonomous Firmware

I’ve seen a number of walkthroughs detailing how to convert an Aironet Wireless Access Point that’s using the lightweight firmware (the firmware which relies on something like a CAPWAP server to provide configuration so there’s not much in the way of local config options) to the autonomous firmware (one with local config & a management GUI). A few people encounter issues because downloading firmware requires a TACACS agreement — great if you’re a network engineer at a company, not great if you’ve bought a single access point somewhere.

While “google it and find someone who has posted the file … then verify the MD5 sum checks out” is an answer, a lot of the newer firmwares appear to have a major bug where any attempt to commit changes yields a 404 error. ap3g2-k9w7-tar.153-3.JF12.tar, ap3g2-k9w7-tar.153-3.JF15.tar, ap3g2-k9w7-tar.153-3.JPI4.tar — all very buggy.  While it may be possible to use the CLI to “copy ru star” and write the running config into the startup config … that’s going to be difficult to explain to someone else. Something else odd — the built-in Cisco account is a ‘read only’ user — this may be normal where the GUI shows it as read only but it’s actually got management permission?

What I’ve realized, in our attempt to convert into a fully functional autonomous firmware, is that the specific version referenced in one of the walkthroughs (ap3g2-k9w7-tar.153-3.JH.tar) is a deliberate selection — it’s a security update firmware release. Which means it’s available for download for anyone with a Cisco account that’s OK for encryption download (i.e. not residing in one of those countries to which American companies are not allowed to ‘export’ good encryption stuff) even if you don’t have a TACACS account.

Luckily, the JH iteration of the firmware doesn’t have the 404 error on committing changes. The Cisco account is still showing up as read-only, but we were able to make our own read-write user & implement changes.

On Federated Identity Providers

The basic idea here is that you may want someone to be able to validate your users without actually having access to your passwords or directory data. As a counter-example, a company I work with has their payroll “stuff” outsourced. Doing so required a B2B VPN that allowed the hosting company to access an internal LDAP directory. I set up an access control list for their connection so they could only authenticate users. Someone at the hosting company couldn’t download all of the e-mail addresses or phone numbers. Even so, a sufficiently motivated employee of the third-party company could get the logon and password for anyone who used their server – if it’s my code, adding the equivalent of ‘fileHandle.write(f”u:{username} p:{password}”)’ would write a log file with every cred used on the site.

Don’t contract with dodgy companies that are going to drop your user creds out to a file and do malicious stuff is a good start, but I would concede that “avoid dodgy companies” isn’t a great security paradigm.  Someone came up with this “federated identity” methodology — instead of you asking the user for their ID and password, you get a URL to redirect not-yet-logged-on users over to someone trusted to handle passwords. This is the “identify provider”, or IDP.

I access your website (called the ‘service provider’, or SP), and you see I don’t have any sort of auth cookie to get me logged in. You forward my browser, along with some header info, over to IdentityProviderSite. IdentityProviderSite says to the end user “hey, what is your username and password”, checks that what is entered, maybe does the MFA “really, prove it” thing, and then redirects the browser back to the originating website. It includes some header stuff that says “Hi, I am IdentityProviderSite and I used my trusted private key to sign this message. I promise that the person associated with this connection is really Lisa. And here’s her important info (could just be username, could be first name, last name, email address, etc) that you can also trust is right.” No idea why, but the info about the person is called an “assertion” — so you’ll see talk about mapping assertions (which is basically telling my application that the thing it calls “logonID” is going to be called “userID” or “uid” or whatever in the data coming from IdentityProviderSite). Voila, I’m now on your website and logged in even though my password never transited your system. All you ever got was a promise that the person on this connection is really Lisa.

To accomplish this, there is a ‘trust’ between an application & an identity provider — if you tried to send a web user to IdentityProviderSite without establishing such a trust, it would say “yeah, I’m not validating users for you — I have no idea who you are”. And, similarly, a web app isn’t going to just trust any random source to say “really, I promise this is Lisa”. So we go into the web application and say “I really, really want to trust IdentityProviderSite when it tells me a user’s ID” and then go into IdentityProviderSite and say “I want WebApp to be able to ask to validate users”. And there’s some crypto stuff because IdentityProviderSite signs it’s “I promise this is Lisa” message & we don’t want someone to be able to edit that to say “I promise this is Fred”.

Why, oh why, is “where to send the authenticated person back to continue on their merry way” called an Assertion Consumer Service? The “service provider” is supposed to “consume” the identity … so it’s the URL of the “assertion consumer” (i.e. the code in the application that has some clue what to do with the “I promise this is Lisa” blob of data that they call an assertion).

Does this make any sense for third-party companies that we really shouldn’t trust? Companies that aren’t located on our internal network to access our directories directly? Absolutely! Does this make any sense for our internal stuff? Stuff with direct, encrypted access to the AD directory? Eh … it goes well with the “trust no one” security principal. And points for consistency — every app’s logon will look the same. But it’s a lot of overhead / Internet traffic / complexity, too.

The basic process flow when a user attempts to use a site is:

  1. A client attempts to access some web resource to which they are not already authenticated
  2. The end web application redirects the client to the Identity Provider.
  3. The Identity Provider authenticates the user.
  4. The Identity Provider redirects the client to the Assertion Consumer Service (ACS) on the web resource by sending a SAML response over HTTP POST.
  5. The web server processes the SAML response.
  6. The client is redirected to the actual web application URL
  7. The web server authorizes the user to access the requested web resource.
  8. The application server sends the HTTP response back to client.

Useful DNF Commands

Beyond basic stuff like “dnf install somepackage” or downloading an rpm and using “dnf install my.package.rpm”, this is a running list of useful dnf commands.

List installed packages (similar to rpm -qa):

dnf list installed

List packages with updates available:

dnf check-update

Update everything but the kernel:
dnf update -x kernel*

Find package that provides something:

[lisa@rhel1 ~/]# dnf whatprovides cdrskin
Last metadata expiration check: 2:35:57 ago on Fri 12 Aug 2022 11:37:43 AM EDT.
cdrskin-1.5.2-2.fc32.x86_64 : Limited cdrecord compatibility wrapper to ease migration to libburn
Repo : fedora
Matched from:
Provide : cdrskin = 1.5.2-2.fc32

cdrskin-1.5.4-2.fc32.x86_64 : Limited cdrecord compatibility wrapper to ease migration to libburn
Repo : updates
Matched from:
Provide : cdrskin = 1.5.4-2.fc32

Package info, including version

[lisa@rhel1 ~/]# dnf info sendmail
Last metadata expiration check: 2:37:19 ago on Fri 12 Aug 2022 11:37:43 AM EDT.
Available Packages
Name : sendmail
Version : 8.15.2
Release : 43.fc32
Architecture : x86_64
Size : 730 k
Source : sendmail-8.15.2-43.fc32.src.rpm
Repository : fedora
Summary : A widely used Mail Transport Agent (MTA)
URL : http://www.sendmail.org/
License : Sendmail
Description : The Sendmail program is a very widely used Mail Transport Agent (MTA).
: MTAs send mail from one machine to another. Sendmail is not a client
: program, which you use to read your email. Sendmail is a
: behind-the-scenes program which actually moves your email over
: networks or the Internet to where you want it to go.
:
: If you ever need to reconfigure Sendmail, you will also need to have
: the sendmail-cf package installed. If you need documentation on
: Sendmail, you can install the sendmail-doc package.

Show history:

[lisa@rhel1 ~/]# dnf history
ID     | Command line                                                                                                      | Date and time    | Action(s)      | Altered
------------------------------------------------------------------------------------------------------------------------------------------------------------------------
   102 | remove liberation-fonts                                                                                           | 2021-11-28 18:44 | Removed        |    3
   101 | remove chromedriver                                                                                               | 2021-11-28 18:44 | Removed        |    2
   100 | remove google-chrome-stable                                                                                       | 2021-11-28 18:44 | Removed        |    1  < 99 | install liberation-fonts | 2021-11-28 18:42 | Install | 1 >
    98 | install chromedriver                                                                                              | 2021-11-28 18:38 | Install        |    2
    97 | remove mediainfo                                                                                                  | 2021-11-16 13:31 | Removed        |    4
    96 | install mediainfo                                                                                                 | 2021-11-16 13:29 | Install        |    4

 

Which brings up an interesting command — you can undo a history step instead of trying to uninstall the list of things you just installed.

dnf history undo 98 -y

Adding Sony SNC-DH220T Camera to Zoneminder

We recently picked up a mini dome IP camera — much better resolution than the old IP cams we got when Anya was born — and it took a little trial-and-error to get it set up in Zoneminder. The first thing we did was update the firmware using Sony’s SNCToolbox, configure the camera as we wanted it, and add a “Viewer” user for zoneminder.

With all that done, the trick is to add an FFMPEG source with the right RTSP address. On the ‘General’ tab, select “Ffmpeg” as the source type:

On the ‘Source’ tab, you need to use the right source path. For video stream one, that is rtsp://zmuser:password@mycamera.example.com/media/video1 — change video1 to video2 for the second video stream, if available. And, obviously, use the account you created on your camera for zoneminder and whatever password. Since it’s something that gets stored in clear text, I make a specific zmuser account with a password we don’t use elsewhere. We’ve used both ‘TCP’ and ‘UDP’ successfully, although there was a lot of streaking with UDP.

Save, give it a minute, and voila … you’ve got a Sony SNC-DH220T camera in Zoneminder!

 

 

Using Screen to Access Console Port

We needed to console into some Cisco access points — RJ45 to USB to plug into the device console port and the laptop’s USB port? Check! OK … now what? Turns out you can use the screen command as a terminal emulator. The basic syntax is screen <port> <baud rate> — since the documentation said to use 9600 baud and the access point showed up on /dev/ttyUSB0, this means running:

 

screen /dev/ttyUSB0 9600

More completely, screen <port> <baud rate>,<7 or 8 bits per byte>,<enable or disable sending flow control>,<enable or disable rcving flow control>,<keep or clear the eight bit in each byte>

screen /dev/ttyUSB0 9600,cs8,ixon,ixoff,istrip 
- or - 
screen /dev/ttyUSB0 9600,cs7,-ixon,-ixoff,-istrip

NGINX Auth Proxy

This example uses Kerberos for SSO authentication using Docker-ized NGINX. To instantiate the sandbox container, I am mapping the conf.d folder into the container and publishing ports 80 and 443

docker run -dit --name authproxy -v /usr/nginx/conf.d:/etc/nginx/conf.d -p 80:80 -p 443:443 -d centos:latest

Shell into the container, install Kerberos, and configure it to use your domain (in this example, it is my home domain.

docker exec -it authproxy bash

# Fix the repos – this is a docker thing, evidently …
cd /etc/yum.repos.d/
sed -i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS-*
sed -i 's|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g' /etc/yum.repos.d/CentOS-*
# And update everything just because
dnf update
# Install required stuff
dnf install vim wget git gcc make pcre-devel zlib-devel krb5-devel

Install NGINX from source and include the spnego-http-auth-nginx-module module

wget http://nginx.org/download/nginx-1.21.6.tar.gz
gunzip nginx-1.21.6.tar.gz
tar vxf nginx-1.21.6.tar
cd nginx-1.21.6/
git clone https://github.com/stnoonan/spnego-http-auth-nginx-module.git
dnf install gcc make pcre-devel zlib-devel krb5-devel
./configure --add-module=spnego-http-auth-nginx-module
make
make install

Configure Kerberos on the server to use your domain:

root@aadac0aa21d5:/# cat /etc/krb5.conf
includedir /etc/krb5.conf.d/
[logging]
default = FILE:/var/log/krb5libs.log
kdc = FILE:/var/log/krb5kdc.log
admin_server = FILE:/var/log/kadmind.log
[libdefaults]
dns_lookup_realm = false
ticket_lifetime = 24h
renew_lifetime = 7d
forwardable = true
rdns = false
default_realm = EXAMPLE.COM
# allow_weak_crypto = true
# default_tgs_enctypes = arcfour-hmac-md5 des-cbc-crc des-cbc-md5
# default_tkt_enctypes = arcfour-hmac-md5 des-cbc-crc des-cbc-md5
default_ccache_name = KEYRING:persistent:%{uid}
[realms]
EXAMPLE.COM= {
   kdc = DC01.EXAMPLE.COM
   admin_server = DC01.EXAMPLE.COM
}

Create a service account in AD & obtain a keytab file:

ktpass /out nginx.keytab /princ HTTP/docker.example.com@example.com -SetUPN /mapuser nginx /crypto AES256-SHA1 /ptype KRB5_NT_PRINCIPAL /pass Th2s1sth3Pa=s -SetPass /target dc01.example.com

Transfer the keytab file to the NGINX server. Add the following to the server{} section or location{} section to require authentication:

auth_gss on;
auth_gss_keytab /path/to/nginx/conf/nginx.keytab;
auth_gss_delegate_credentials on;

You will also need to insert header information into the nginx config:

proxy_pass http://www.example.com/authtest/;
proxy_set_header Host "www.example.com"; # I need this to match the host header on my server, usually can use data from $host
proxy_set_header X-Original-URI $request_uri; # Forward along request URI
proxy_set_header X-Real-IP $remote_addr; # pass on real client's IP
proxy_set_header X-Forwarded-For "LJRAuthPrxyTest";
proxy_set_header X-Forwarded-Proto $scheme;
proxy_set_header Authorization $http_authorization;
proxy_pass_header Authorization;
proxy_set_header X-WEBAUTH-USER $remote_user;
proxy_read_timeout 900;

Run NGINX: /usr/local/nginx/sbin/nginx

In and of itself, this is the equivalent of requiring authentication – any user – to access a site. The trick with an auth proxy is that the server must trust the header data you inserted – in this case, I have custom PHP code that looks for X-ForwardedFor to be “LJRAuthPrxyTest” and, if it sees that string, reads X-WEBAUTH-USER for the user’s logon name.

In my example, the Apache site is configured to only accept connections from my NGINX instance:

<RequireAll>
     Require ip 10.1.3.5
</RequireAll>

This prevents someone from playing around with header insertion and spoofing authentication.

Some applications allow auth proxying, and the server documentation will provide guidance on what header values need to be used.

 

Using urandom to Generate Password

Frequently, I’ll use password generator websites to create some pseudo-random string of characters for system accounts, database replication,etc. But sometimes the Internet isn’t readily available … and you can create a decent password right from the Linux command line using urandom.

If you want pretty much any “normal” character, use tr to pull out all of the other characters:

'\11\12\40-\176'

Or remove anything outside of upper case, lower case, and number characters using

a-zA-Z0-9

Pass the output to head to grab however many characters you actually want. Voila — a quick password.