## TL;DR
A segfault during NSE means one script, or a corrupted script database, is crashing the whole engine rather than failing cleanly. Bisect by running version detection alone, then a single safe script, then script groups, and repair the install or exclude the one broken script so the authorized scan can finish.

```text
nmap segmentation fault during NSE script scan of authorized target
```

## Use this when
- nmap crashes with a segmentation fault as soon as -sC or a named script starts.
- Plain port scanning of the same in-scope host completes normally.

## Not for this skill when
- A script prints an error and nmap finishes. That is a script logic fault to fix in the script arguments, not a segfault.
- The crash happens on every host including loopback with no scripts loaded. Suspect a broken binary or library first.

## Steps
1. Reproduce minimally on one in-scope host: run a plain connect scan, then add -sV, then add one safe script such as http-title. Verify: Verify: you can name the exact step where the crash first appears.
2. Run with script tracing and debugging, nmap -d with --script-trace, and save the last script name printed before the fault. Verify: Verify: the log ends on the same script across two runs.
3. Refresh the script database with nmap --script-updatedb and check the nmap and OpenSSL versions for a mismatched local build. Verify: Verify: the database rebuild completes and nmap --version shows a coherent build.
4. Reinstall nmap from the distro package or rebuild it, then rerun the failing script alone against the authorized host. Verify: Verify: the single-script run finishes and writes normal output.
5. If one community script still crashes, exclude it with --script excluding that name, note the gap in coverage, and report the crash upstream with the trace. Verify: Verify: the full scan completes and the engagement log records the excluded script.

## Variant phrasings
### nmap crashes when running vuln scripts segfault
The category-level phrasing when -sC or vuln scripts trigger it.
### nmap script scan core dumped linux
The shell-message phrasing from the tester box.
### one nse script crashes whole nmap scan
The isolation phrasing after bisecting.

Compatibility: Compatibility: nmap 7.x NSE on Linux; package reinstall steps assume a distro or official build, not a hand-patched fork.

## Why it happens
NSE scripts run inside one process, so a native crash in a library a script loads, or a corrupt compiled script entry, takes nmap down with it. The port scan core is usually healthy; the fault surface grows only when the script engine loads that specific script and its dependencies.

## Edge cases / pitfalls
- Do not debug by scanning harder: one host, one script, minimal ports keeps the authorized target load low.
- A segfault after a distro upgrade often means a stale locally built nmap is picking up new system libraries; check which binary the shell resolves.
- Keep the core dump and the exact command line; both belong in the upstream report and the engagement notes.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_jVToOdYfj6xEN5dHXfeOHg