During a Nessus scan of a network it was showing lots of insecurities with an NSClient configuarion on a windows machine we were monitoring via Nagios.
OS: Windows 2016 NSClient: 0.3.x Nagios: 4.0.7
Looking at one particular issue (SSLv2 and SSLv3) showing on the report:
The remote service accepts connections encrypted using SSL 2.0 and/or SSL 3.0. These versions of SSL are affected by several cryptographic flaws, including:
– An insecure padding scheme with CBC ciphers.
– Insecure session renegotiation and resumption schemes.
An attacker can exploit these flaws to conduct man-in-the-middle attacks or to decrypt communications between the affected service and clients.
Although SSL/TLS has a secure means for choosing the highest supported version of the protocol (so that these versions will be used only if the client or server support nothing better), many web browsers implement this in an unsafe way that allows an attacker to downgrade a connection (such as in POODLE). Therefore, it is recommended that these protocols be disabled entirely.
NIST has determined that SSL 3.0 is no longer acceptable for secure communications. As of the date of enforcement found in PCI DSS v3.1, any version of SSL will not meet the PCI SSC's definition of 'strong cryptography'.
Consult the application's documentation to disable SSL 2.0 and 3.0.
Use TLS 1.1 (with approved cipher suites) or higher instead.
- SSLv3 is enabled and the server supports at least one cipher.
Port Hosts 5666 / tcp
Our Nagios server connects to the NS Client on the Windows machine via 12489. Port 5666 is not required. However NRPE listener was seemingly started by default. As we did not require this port to be listening we just stopped the NRPE service from starting:
1) Open the nsclient/NCSA config file (eg C:\Program Files\NSClient++\NSC) and comment out the NRPEListener.dll like so
Note: in later versions of the NSClient you can just disable the SSL values but as we didnt even require NRPE to be listening we simply stopped the service.