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Feat/agent validate webcert#259

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Ylianst merged 8 commits intoYlianst:masterfrom
HuFlungDu:feat/agent-validate-webcert
Feb 16, 2026
Merged

Feat/agent validate webcert#259
Ylianst merged 8 commits intoYlianst:masterfrom
HuFlungDu:feat/agent-validate-webcert

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@HuFlungDu
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Added an option to have the agent validate the webcert of the server to which it is connected. This is valuable in the case of a DNS hijack or MITM, which currently is possible if a bad actor can gain access to the meshcentral agent cert, and that cert can't be rotated or expired.

This is accomplished by adding validateWebCert=true in the msh file. It will continue to run as normal until such time as that value is set.

Once this is gone over, I will create a PR in the Meshcentral repo to update the meshcore and add a config option to have this option set on your agents by default.

Old implementation didn't work, it would crash when it tried to dereference and set a null pointer (*x = i). This version works by setting the default size to destinationSize, so it will throw in the later check if no \0 is found. This function is otherwise unused in the code.
Windows doesn't respect the openssl standard, so that needed to be handled manuall.

Since this project uses a statically linked openssl, the default locations may be inaccurate. If that directory doesn't exist, it tries to get it from the system openssl via a popen. If that also fails, it will not be able to load system certs.
…ta to the callback.

This was necessary to get a handle on the agent during the connection callback.
This will cause the connection to fail if the value is set and the agent attempts to connect to a server with an invalid web certificate
Before it would override any user defined checks; now it will foil to connect if the system certs don't match, but will still run user checks if it passes those.
This will cause rejectUnauthorized to be true if you pass it in
@HuFlungDu
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@Ylianst , Can I get a description of what would need to be implemented in order for this or something that accomplishes this effect to be merged?

@Ylianst Ylianst merged commit 4a34966 into Ylianst:master Feb 16, 2026
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Ylianst commented Feb 16, 2026

I will take this, but please don't add validateWebCert=true by default since: this will break most Meshcentral installation.

  • A lot of people use Meshcentral for private use and don't have a public certificate.
  • Some IOT devices do not have up to date certificates and so, will fail to connect to the server like older Windows and Linux machines.
  • If someone can remove a trusted cert from the system, it will cause the agent to not correct, causing a denial of service issue.

The goal of the agent was to connect to the server with minimal dependency on the system's configuration and deal with situation where DNS is not available, etc. It's ok to add this check, but at the administrator's own risk.

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2 participants