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Red Hat Reports a Flow in Sudo


Red Hat reports a flow in sudo. They found a heap-based buffer overflow in the way sudo parses command line arguments. This flaw is exploitable by any local user. Counts for normal users and system users, sudo-ers and non-sudo-ers, without authentication. Meaning: the attacker does not need to know the user’s password. Successful exploitation of this flaw could lead to privilege escalation. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.

Read here the complete article.

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Zabbix Getting your notifications via Signal

Recently, Whatsapp pushed their new privacy policy where they announced to share more data with Facebook, causing an exodus to other platforms, where Signal is one of the more popular ones, among Telegram. Both are great alternatives, but I prefer Signal due to the open-source part, end to end encryption, and last but not least: their business model (living on donations instead of selling your data) and not to forget: we can use Zabbix getting your notifications via Signal.

Typically, Zabbix is sending notifications to whatever medium you’ve chosen if a problem is detected. We all know the Email messages, the various webhook integrations with Slack/MS Teams/ Jira, etc, perhaps even some text message integrations and such. Now, if we’re migrating to Signal, we suddenly have access to the Signal API and can utilize it to receive Zabbix notifications. Nice!

There is only one drawback. You need a separate phone number to register against Signal. Don’t use your own phone number – unless you want to lose the ability to use Signal ;(

There are various ways to get a phone number for this purpose:

  • Use the phone number of your current SMS gateway
  • Use the company phone number (a lot of cloud PBX are providing the option to receive the verification email)
  • Purchase a prepaid phone number.
  • Use a service like Twilio

You just need to receive one text message, the rest of the communications will go via the internet

Time to get rid of Whatsapp and move to Signal! But… How to use Signal to get your notifications?


Although we could built everything from scratch, talking to the API of Signal, there is a nice implementation available in order to talk to Signal within a few minutes: Signal-cli

Although this github page is very comprehensive in order to get Signal-cli installed, but of course it is not doing anything with Zabbix.

Configuration tasks

For this guide, we’re using:

  • Centos 8
  • Zabbix 5.2

signal-cli installation

First, lets install the Signal-cli utility, and in order to do so we need to resolve the dependency of Java by installing the openjdk application:

dnf -y install java-11-openjdk-devel.x86_64

After this installation, we should be good to continue with the installation of signal-cli. According to their installation guide, this should be sufficient:

export VERSION="0.7.3"
sudo tar xf signal-cli-"${VERSION}".tar.gz -C /opt
sudo ln -sf /opt/signal-cli-"${VERSION}"/bin/signal-cli /usr/local/bin/

At the time of writing, the most recent version is 0.7.3, and that’s what we’re installing here. If in the future a new version is released, of course you should install that!

If everything went as expected, we should be able to register ourself to Signal.

signal-cli registration

Since we want to execute these commands by Zabbix, we must make sure the registration is done with the correct user on the Zabbix server, otherwise you will get the following error message:

Unregistered user error

(ERROR App – User +19293771253 is not registered.)

In order to prevent this error, lets do the authentication against Signal as Zabbix user:

Important: The USERNAME (your phone number) must include the country calling code, i.e. the number must start with a “+” sign and you must replace everything between the  < > in the following examples with your own values

runuser -l zabbix -c 'signal-cli -u <NUMBER> register'

Now, check for incoming test messages on this phone number. Within seconds you should receive a 6 digit code in the following format: xxx-xxx

Once you’ve received the text, it’s time to complete the registration:

runuser -l zabbix -c 'signal-cli -u <NUMBER> verify <CODE>'

Since we’re running these commands as a different user, we won’t see the output of them. Let’s just test!

Sending messages from the command line is straight forward:

runuser -l zabbix -c 'signal-cli -u <NUMBER> send -m <MESSAGE> <RECEIVER NUMBER>'

You will see the message id as output. Simply ignore it, since it’s not relevant at this point.

Within seconds:

It works! Great.

So now we’ve got this part covered, time to get the AlertScript set up, before heading to the frontend.

Zabbix AlertScript setup

Ok, so now we’ve got the registration done, we need to make sure Zabbix can utilise it. In order to do so, we use a very old method. Although it would’ve made more sense to use the webhook option, that means I had to built the communication with Signal from scratch.

So AlertScripts it is. In your terminal/SSH session with the Zabbix server open a new file with this command: vi /usr/lib/zabbix/alertscripts/ and insert the following contents:

signal-cli -u '+19293771253' send -m "$1" $2

 That’s right. just 2 lines. After saving the file, change the owner and set the permissions:

chown zabbix:zabbix /usr/lib/zabbix/alertscripts/
chmod 7000 /usr/lib/zabbix/alertscripts/

and it’s time to move to our frontend.

Zabbix mediatype configuration

In the frontend, go to Administration -> Mediatypes and create a new mediatype:

Signal Mediatype
Name: Signal
Type: Script
Script name:
Script parameters:

don’t forget to configure some Message templates as well (second tab in the Mediatype configuration). You can just use the defaults if you click on ‘add’

Zabbix media configuration

Next step. Navigate to Administration -> Users (or just open your own user profile) and create a new media:

Type: Signal
Sendto: <your number>
When active / severity as per needs

Important: The USERNAME (your phone number) must include the country calling code, i.e. the number must start with a “+” sign

We’re almost there, just some configuration on the actions

Zabbix action configuration

This step is only needed if you are sending notifications right now via a specific mediatype. If you configured the ‘send only to’ option to ‘- All -‘ there is nothing to change, and it will work straight away!

Otherwise, navigate to Configuration -> Actions and find the action you want to change, and in the Operations, Recovery operations and Update operations change the ‘send only to’ option to ‘Signal’

Save your action and it’s time to test – Generate some problem to confirm the implementation actually works.

Wrap up

That’s it. By now you should have a working implementation where Zabbix is sending notifications to Signal. The setup was extremely straight forward and easy to configure. Nevertheless, if you need help getting this going, we (Opensource ICT Solutions) offer consultancy services as well, and are more than happy to help you out!

Partner News

Managing Windows with Puppet

Managing windows with Puppet, not possible? Puppet manages over 2.2 million Windows servers across the world!

There is a lot more to effectively managing Windows than Group Policy and SCCM, and Puppet is here to help.

Join Puppet on 25 February 2021 from 10:00am SGT | 1:00pm AEDT for our upcoming webinar to find out the richness of our ecosystem for managing Windows with Puppet. Click here to register.

Find out here about our Puppet training offerings.

Partner News

Zabbix agent supports Microsoft Exchange Server 2016

Microsoft Exchange Server is a mail server and calendaring server developed by Microsoft. It runs exclusively on Windows Server operating systems. Explore the new official template for Microsoft Exchange Server 2016.

Click here for more information.

Partner News

Puppet CEO is gearing up to take the company public.


She has her hands full. She’s overseeing an ambitious open source-based company on the cusp of going public with $40 million in fresh capital. These come from funds led by Blackrock in the bank, and busy adding purpose built business solutions for compliance, security, and self-service at the company.

The former VMware executive is among the rare breed of CIOs (for two years at observability platform New Relic) to have stepped into the CEO role. Along with 25 years of experience scaling companies globally in a range of leadership roles, she retains hands-on technical chops, having started out as a software engineer at Accenture (“back when COBOL was cool”; The Stack: “COBOL‘s still cool”; Wassenaar: “I’m very employable…”).

Puppet CEO Yvonne Wassenaar: “People tend to commingle public cloud with cloud native…”

She has been at the helm of Portland, Oregon-headquartered  Puppet since January 2019. There she has sharpened focus on specialised tools for larger commercial organisations, and overseen the addition of a wide range of new offerings at the open source-based software configuration management (CM) and deployment provider. Traditionally used to “pull the strings” on multiple application servers simultaneously – as Puppet eyes a chunk of the growing compliance and security markets.

The CEO is gearing up to take the company public later this year. She believes it is ready for after strong numbers last year. She tells The Stack: “In 2020, Puppet’s revenue was north of $100 million. It was growing as we added new customers. We also expanded within our existing enterprise customers and increased the average size of our deals. Our renewal rates are close to 90% and our expansion rates are close to 120%.  Gross margins are +80% and we have a strong profit/loss position for a company of our size”.

To read the full article, click here.

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Let Zabbix Experts Assist You

Zabbix is a powerful open-source monitoring solution, but that’s not the only thing that makes it stand out. Zabbix company develops the software and provides a range of technical services to make the monitoring easy and scalable. Let Zabbix experts assist you @ Open-Future.

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