Script http-slowloris-check

Script types: portrule
Categories: vuln, safe

Script Summary

Tests a web server for vulnerability to the Slowloris DoS attack without actually launching a DoS attack.

Slowloris was described at Defcon 17 by RSnake (see

This script opens two connections to the server, each without the final CRLF. After 10 seconds, second connection sends additional header. Both connections then wait for server timeout. If second connection gets a timeout 10 or more seconds after the first one, we can conclude that sending additional header prolonged its timeout and that the server is vulnerable to slowloris DoS attack.

A "LIKELY VULNERABLE" result means a server is subject to timeout-extension attack, but depending on the http server's architecture and resource limits, a full denial-of-service is not always possible. Complete testing requires triggering the actual DoS condition and measuring server responsiveness.

You can specify custom http User-agent field with http.useragent script argument.

Idea from Qualys blogpost:

See also:

Script Arguments


See the documentation for the slaxml library., http.max-body-size, http.max-cache-size, http.max-pipeline, http.pipeline, http.truncated-ok, http.useragent

See the documentation for the http library.

smbdomain, smbhash, smbnoguest, smbpassword, smbtype, smbusername

See the documentation for the smbauth library.

vulns.short, vulns.showall

See the documentation for the vulns library.

Example Usage

nmap --script http-slowloris-check  <target>

Script Output

80/tcp open  http    syn-ack
| http-slowloris-check:
|   Slowloris DOS attack
|     IDs:  CVE:CVE-2007-6750
|       Slowloris tries to keep many connections to the target web server open and hold
|       them open as long as possible.  It accomplishes this by opening connections to
|       the target web server and sending a partial request. By doing so, it starves
|       the http server's resources causing Denial Of Service.
|     Disclosure date: 2009-09-17
|     References:



  • Aleksandar Nikolic

License: Same as Nmap--See