Nmap http-slowloris-check NSE Script


This page contains detailed information about how to use the http-slowloris-check NSE script. For list of all NSE scripts, visit the Nmap NSE Library.

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Script Overview

Script source code: https://github.com/nmap/nmap/tree/master/scripts/http-slowloris-check.nse
Script categories: vuln, safe
Target service / protocol: http, https
Target network port(s): 80, 443, 631, 7080, 8080, 8443, 8088, 5800, 3872, 8180, 8000
List of CVEs: CVE-2007-6750

Script Description

The http-slowloris-check.nse script 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 http://ha.ckers.org/slowloris/).

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:

Http-slowloris-check NSE Script Arguments

This is a full list of arguments supported by the http-slowloris-check.nse script:

smbdomain

The domain to log in with. If you aren't in a domain environment, then anything will (should?) be accepted by the server.

smbhash

A password hash to use when logging in. This is given as a single hex string (32 characters) or a pair of hex strings (both 32 characters, optionally separated by a single character). These hashes are the LanMan or NTLM hash of the user's password, and are stored on disk or in memory. They can be retrieved from memory using the fgdump or pwdump tools.

smbnoguest

Use to disable usage of the 'guest' account.

smbpassword

The password to connect with. Be cautious with this, since some servers will lock accounts if the incorrect password is given. Although it's rare that the Administrator account can be locked out, in the off chance that it can, you could get yourself in trouble. To use a blank password, leave this parameter off altogether.

smbtype

The type of SMB authentication to use. These are the possible options:

  • v1: Sends LMv1 and NTLMv1.
  • LMv1: Sends LMv1 only.
  • NTLMv1: Sends NTLMv1 only (default).
  • v2: Sends LMv2 and NTLMv2.
  • LMv2: Sends LMv2 only.
  • NTLMv2: Doesn't exist; the protocol doesn't support NTLMv2 alone. The default, NTLMv1, is a pretty decent compromise between security and compatibility. If you are paranoid, you might want to use v2 or lmv2 for this. (Actually, if you're paranoid, you should be avoiding this protocol altogether!). If you're using an extremely old system, you might need to set this to v1 or lm, which are less secure but more compatible. For information, see smbauth.lua.

smbusername

The SMB username to log in with. The forms "DOMAIN\username" and "username@DOMAIN" are not understood. To set a domain, use the smbdomain argument.

slaxml.debug

Debug level at which default callbacks will print detailed parsing info. Default: 3

http.host

The value to use in the Host header of all requests unless otherwise set. By default, the Host header uses the output of stdnse.get_hostname().

http.max-body-size

Limit the received body to specific number of bytes. An oversized body results in an error unless script argument http.truncated-ok or request option truncated_ok is set to true. The default is 2097152 (2MB). Use value -1 to disable the limit altogether. This argument can be overridden case-by-case with request option max_body_size.

http.max-cache-size

The maximum memory size (in bytes) of the cache.

http.max-pipeline

If set, it represents the number of outstanding HTTP requests that should be sent together in a single burst. Defaults to http.pipeline (if set), or to what function get_pipeline_limit returns.

http.pipeline

If set, it represents the number of HTTP requests that'll be sent on one connection. This can be set low to make debugging easier, or it can be set high to test how a server reacts (its chosen max is ignored).

http.truncated-ok

Do not treat oversized body as error. (Use response object flag truncated to check if the returned body has been truncated.) This argument can be overridden case-by-case with request option truncated_ok.

http.useragent

The value of the User-Agent header field sent with requests. By default it is "Mozilla/5.0 (compatible; Nmap Scripting Engine; https://nmap.org/book/nse.html)". A value of the empty string disables sending the User-Agent header field.

vulns.short

If set, vulnerabilities will be output in short format, a single line consisting of the host's target name or IP, the state, and either the CVE ID or the title of the vulnerability. Does not affect XML output.

vulns.showall

If set, the library will show and report all the registered vulnerabilities which includes the NOT VULNERABLE ones. By default the library will only report the VULNERABLE entries: VULNERABLE, LIKELY VULNERABLE, VULNERABLE (DoS) and VULNERABLE (Exploitable). This argument affects the following functions: vulns.Report.make_output(): the default output function for portule/hostrule scripts. vulns.make_output(): the default output function for postrule scripts. vulns.format_vuln() and vulns.format_vuln_table() functions.

- - -
To use these script arguments, add them to the Nmap command line using the --script-args arg1=value,[arg2=value,..] syntax. For example:

nmap --script=http-slowloris-check --script-args smbdomain=value,smbhash=value <target>

Http-slowloris-check NSE Script Example Usage

Here's an example of how to use the http-slowloris-check.nse script:

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

Http-slowloris-check NSE Script Example Output

Here's a sample output from the http-slowloris-check.nse script:

PORT   STATE SERVICE REASON
80/tcp open  http    syn-ack
| http-slowloris-check:
|   VULNERABLE:
|   Slowloris DOS attack
|     State: LIKELY VULNERABLE
|     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:
|       http://ha.ckers.org/slowloris/
|_      http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-6750

Http-slowloris-check NSE Script Example XML Output

There is no sample XML output for this module. However, by providing the -oX <file> option, Nmap will produce a XML output and save it in the file.xml file.

Author

  • Aleksandar Nikolic

References

See Also

Related NSE scripts to the http-slowloris-check.nse script:

Visit Nmap NSE Library for more scripts.

The http-slowloris-check.nse script may fail with the following error messages. Check for the possible causes by using the code snippets highlighted below found in the script source code. This can often times help in identifying the root cause of the problem.

Error determining SSL: %s

Here is a relevant code snippet related to the "Error determining SSL: %s" error message:

92:	  slowloris.state = vulns.STATE.NOT_VULN
93:	
94:	  local sd, response, Bestopt = comm.tryssl(host, port, "GET / HTTP/1.0\r\n\r\n") -- first determine if we need ssl
95:	  if sd then sd:close() end
96:	  if Bestopt == "none" then
97:	    stdnse.debug1("Error determining SSL: %s", response)
98:	    return nil
99:	  end
100:	  local HalfHTTP = (
101:	    "POST /" .. tostring(math.random(100000, 900000)) .. " HTTP/1.1\r\n" ..
102:	    "Host: " .. host.ip .. "\r\n" ..

Unable to time responses: thread died early.

Here is a relevant code snippet related to the "Unable to time responses: thread died early." error message:

147:	    end
148:	    stdnse.sleep(1)
149:	  end
150:	  -- compare times
151:	  if ( not(TimeWith) or not(TimeWithout) ) then
152:	    stdnse.debug1("Unable to time responses: thread died early.")
153:	    return nil
154:	  end
155:	  local diff = TimeWith - TimeWithout
156:	  stdnse.debug1("Time difference is: %.f",diff)
157:	  -- if second connection died 10 or more seconds after the first

Version

This page has been created based on Nmap version 7.92.

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