Apache 2.2.x < 2.2.21 mod_proxy_ajp DoS

#
# (C) Tenable Network Security, Inc.
#

include("compat.inc");

if (description)
{
  script_id(56216);
  script_cvs_date("Date: 2018/06/29 12:01:03");
  script_version("1.16");

  script_cve_id("CVE-2011-3348");
  script_bugtraq_id(49616);

  script_name(english:"Apache 2.2.x < 2.2.21 mod_proxy_ajp DoS");
  script_summary(english:"Checks version in Server response header.");
 
 script_set_attribute(attribute:"synopsis", value:
"The remote web server is affected by a denial of service
vulnerability.");
 script_set_attribute(attribute:"description", value:
"According to its banner, the version of Apache 2.2.x running on the
remote host is prior to 2.2.21. It is, therefore, potentially affected
by a denial of service vulnerability. An error exists in the
'mod_proxy_ajp' module that can allow specially crafted HTTP requests
to cause a backend server to temporarily enter an error state. This
vulnerability only occurs when 'mod_proxy_ajp' is used along with
'mod_proxy_balancer'.

Note that Nessus did not actually test for the flaws but instead has
relied on the version in the server's banner.");
  script_set_attribute(attribute:"see_also", value:"https://archive.apache.org/dist/httpd/CHANGES_2.2.21");
  script_set_attribute(attribute:"see_also", value:"http://httpd.apache.org/security/vulnerabilities_22.html");
  script_set_attribute(attribute:"solution", value:
"Upgrade to Apache version 2.2.21 or later.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:M/Au:N/C:N/I:N/A:P");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C");
  script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"false");

  script_set_attribute(attribute:"vuln_publication_date", value:"2011/09/14");
  script_set_attribute(attribute:"patch_publication_date", value:"2011/09/14");
  script_set_attribute(attribute:"plugin_publication_date", value:"2011/09/16");

  script_set_attribute(attribute:"plugin_type", value:"remote");
  script_set_attribute(attribute:"cpe", value:"cpe:/a:apache:http_server");
  script_end_attributes();
 
  script_category(ACT_GATHER_INFO);
  script_family(english:"Web Servers");

  script_copyright(english:"This script is Copyright (C) 2011-2018 Tenable Network Security, Inc.");

  script_dependencies("apache_http_version.nasl");
  script_require_keys("installed_sw/Apache");
  script_require_ports("Services/www", 80);

  exit(0);
}

include("global_settings.inc");
include("misc_func.inc");
include("http.inc");
include("audit.inc");
include("install_func.inc");

get_install_count(app_name:"Apache", exit_if_zero:TRUE);
port = get_http_port(default:80);
install = get_single_install(app_name:"Apache", port:port, exit_if_unknown_ver:TRUE);

# Check if we could get a version first, then check if it was
# backported
version = get_kb_item_or_exit('www/apache/'+port+'/version', exit_code:1);
backported = get_kb_item_or_exit('www/apache/'+port+'/backported', exit_code:1);

if (report_paranoia < 2 && backported) audit(AUDIT_BACKPORT_SERVICE, port, "Apache");
source = get_kb_item_or_exit('www/apache/'+port+'/source', exit_code:1);

# Check if the version looks like either ServerTokens Major/Minor
# was used
if (version =~ '^2(\\.2)?$') exit(1, "The banner from the Apache server listening on port "+port+" - "+source+" - is not granular enough to make a determination.");

if (version !~ "^\d+(\.\d+)*$") exit(1, "The version of Apache listening on port " + port + " - " + version + " - is non-numeric and, therefore, cannot be used to make a determination.");

fixed_ver = '2.2.21';
if (version =~ '^2\\.2' && ver_compare(ver:version, fix:fixed_ver) == -1)
{
  if (report_verbosity > 0)
  {
    report = 
      '\n  Version source    : ' + source +
      '\n  Installed version : ' + version +
      '\n  Fixed version     : ' + fixed_ver + '\n';
    security_warning(port:port, extra:report);
  }
  else security_warning(port);
  exit(0);
}
else audit(AUDIT_LISTEN_NOT_VULN, "Apache", port, install["version"]);