Asterisk DoS Vulnerability (AST-2021-005)

# SPDX-FileCopyrightText: 2021 Greenbone AG
# Some text descriptions might be excerpted from (a) referenced
# source(s), and are Copyright (C) by the respective right holder(s).
#
# SPDX-License-Identifier: GPL-2.0-only

CPE = "cpe:/a:digium:asterisk";

if (description)
{
  script_oid("1.3.6.1.4.1.25623.1.0.145420");
  script_version("2023-12-19T05:05:25+0000");
  script_tag(name:"last_modification", value:"2023-12-19 05:05:25 +0000 (Tue, 19 Dec 2023)");
  script_tag(name:"creation_date", value:"2021-02-19 04:16:47 +0000 (Fri, 19 Feb 2021)");
  script_tag(name:"cvss_base", value:"4.3");
  script_tag(name:"cvss_base_vector", value:"AV:N/AC:M/Au:N/C:N/I:N/A:P");
  script_tag(name:"severity_vector", value:"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H");
  script_tag(name:"severity_origin", value:"NVD");
  script_tag(name:"severity_date", value:"2021-02-24 17:03:00 +0000 (Wed, 24 Feb 2021)");

  script_cve_id("CVE-2021-26906");

  script_tag(name:"qod_type", value:"remote_banner_unreliable");

  script_tag(name:"solution_type", value:"VendorFix");

  script_name("Asterisk DoS Vulnerability (AST-2021-005)");

  script_category(ACT_GATHER_INFO);

  script_copyright("Copyright (C) 2021 Greenbone AG");
  script_family("Denial of Service");
  script_dependencies("gb_digium_asterisk_sip_detect.nasl");
  script_mandatory_keys("digium/asterisk/detected");

  script_tag(name:"summary", value:"Asterisk is prone to a denial of service vulnerability in the
  PJSIP channel driver.");

  script_tag(name:"vuldetect", value:"Checks if a vulnerable version is present on the target host.");

  script_tag(name:"insight", value:"Given a scenario where an outgoing call is placed from Asterisk
  to a remote SIP server it is possible for a crash to occur.

  The code responsible for negotiating SDP in SIP responses incorrectly assumes that SDP negotiation
  will always be successful. If a SIP response containing an SDP that can not be negotiated is
  received a subsequent SDP negotiation on the same call can cause a crash.

  If the 'accept_multiple_sdp_answers' option in the 'system' section of pjsip.conf is set to 'yes'
  then any subsequent non-forked SIP response with SDP can trigger this crash.

  If the 'follow_early_media_fork' option in the 'system' section of pjsip.conf is set to 'yes' (the
  default) then any subsequent SIP responses with SDP from a forked destination can trigger this
  crash.

  If a 200 OK with SDP is received from a forked destination it can also trigger this crash, even if
  the 'follow_early_media_fork' option is not set to 'yes'.

  In all cases this relies on a race condition with tight timing where the second SDP negotiation
  occurs before termination of the call due to the initial SDP negotiation failure.");

  script_tag(name:"affected", value:"Asterisk Open Source 13.x, 16.x, 17.x, 18.x and 16.x Certified
  Asterisk.");

  script_tag(name:"solution", value:"Update to version 13.38.2, 16.16.1, 17.9.2, 18.2.1, 16.8-cert6
  or later.");

  script_xref(name:"URL", value:"https://downloads.asterisk.org/pub/security/AST-2021-005.html");

  exit(0);
}

include("host_details.inc");
include("revisions-lib.inc");
include("version_func.inc");

if (!port = get_app_port(cpe: CPE))
  exit(0);

if (!version = get_app_version(cpe: CPE, port: port))
  exit(0);

if (version =~ "^13\.") {
  if (version_is_less(version: version, test_version: "13.38.2")) {
    report = report_fixed_ver(installed_version: version, fixed_version: "13.38.2");
    security_message(port: port, data: report, proto: "udp");
    exit(0);
  }
}

if (version =~ "^16\.") {
  if (version =~ "^16\.[0-9]cert") {
    if (revcomp(a: version, b: "16.8cert6") < 0) {
      report = report_fixed_ver(installed_version: version, fixed_version: "16.8-cert6");
      security_message(port: port, data: report, proto: "udp");
      exit(0);
    }
  }
  else {
    if (version_is_less(version: version, test_version: "16.16.1")) {
      report = report_fixed_ver(installed_version: version, fixed_version: "16.16.1");
      security_message(port: port, data: report, proto: "udp");
      exit(0);
    }
  }
}

if (version_in_range(version: version, test_version: "17.0", test_version2: "17.9.1")) {
  report = report_fixed_ver(installed_version: version, fixed_version: "17.9.2");
  security_message(port: port, data: report, proto: "udp");
  exit(0);
}

if (version_in_range(version: version, test_version: "18.0", test_version2: "18.2.0")) {
  report = report_fixed_ver(installed_version: version, fixed_version: "18.2.1");
  security_message(port: port, data: report, proto: "udp");
  exit(0);
}

exit(99);