nmap / nmap/npcap

Npcap installer should detect and remediate for NETCFG_E_MAX_FILTER_LIMIT

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current enhancement
Dominant language
C
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Description

As discussed in nmap/nmap#572, Windows 7 has a limit on the number of NDIS filter drivers that can be installed, defaulting to 8 but configurable up to 14. Right now, we detect the specific error and print a message to STDOUT in NPFInstall.exe, but the installer doesn't take any special action on this condition.

I propose 2 changes:

  1. When NETCFG_E_MAX_FILTER_LIMIT is returned, increment HKLM:\SYSTEM\CurrentControlSet\Control\Network\MaxNumFilters and try again.
  2. If the install continues to fail with the same error, fail in such a way that the executable installer can detect and display a useful error message to the user. Existing message is simply "Failed to create the npcap service for Win7, Win8 and Win10. Please try installing Npcap again, or use the latest official Npcap installer from https://nmap.org/npcap/"

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by locating the NETCFG_E_MAX_FILTER_LIMIT handling in NPFInstall.exe and the executable installer’s error path. Review how HKLM:\SYSTEM\CurrentControlSet\Control\Network\MaxNumFilters is accessed and how installation errors are returned. Done means the limit condition is retried with the requested remediation, and repeated failure produces an installer-detectable, useful message.

Written by the indexing model from the issue text.

Assessment

Tech stack
c
Domain
networking, operating-systems
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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