Amazon Linux 2 : dnsmasq (ALAS-2021-1587)

##
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Amazon Linux 2 Security Advisory ALAS-2021-1587.
##

include('compat.inc');

if (description)
{
  script_id(145454);
  script_version("1.3");
  script_set_attribute(attribute:"plugin_modification_date", value:"2022/12/05");

  script_cve_id("CVE-2020-25684", "CVE-2020-25685", "CVE-2020-25686");
  script_xref(name:"ALAS", value:"2021-1587");
  script_xref(name:"CEA-ID", value:"CEA-2021-0003");

  script_name(english:"Amazon Linux 2 : dnsmasq (ALAS-2021-1587)");

  script_set_attribute(attribute:"synopsis", value:
"The remote Amazon Linux 2 host is missing a security update.");
  script_set_attribute(attribute:"description", value:
"The version of dnsmasq installed on the remote host is prior to 2.76-16. It is, therefore, affected by multiple
vulnerabilities as referenced in the ALAS2-2021-1587 advisory.

  - A flaw was found in dnsmasq before version 2.83. When getting a reply from a forwarded query, dnsmasq
    checks in the forward.c:reply_query() if the reply destination address/port is used by the pending
    forwarded queries. However, it does not use the address/port to retrieve the exact forwarded query,
    substantially reducing the number of attempts an attacker on the network would have to perform to forge a
    reply and get it accepted by dnsmasq. This issue contrasts with RFC5452, which specifies a query's
    attributes that all must be used to match a reply. This flaw allows an attacker to perform a DNS Cache
    Poisoning attack. If chained with CVE-2020-25685 or CVE-2020-25686, the attack complexity of a successful
    attack is reduced. The highest threat from this vulnerability is to data integrity. (CVE-2020-25684)

  - A flaw was found in dnsmasq before version 2.83. When getting a reply from a forwarded query, dnsmasq
    checks in forward.c:reply_query(), which is the forwarded query that matches the reply, by only using a
    weak hash of the query name. Due to the weak hash (CRC32 when dnsmasq is compiled without DNSSEC, SHA-1
    when it is) this flaw allows an off-path attacker to find several different domains all having the same
    hash, substantially reducing the number of attempts they would have to perform to forge a reply and get it
    accepted by dnsmasq. This is in contrast with RFC5452, which specifies that the query name is one of the
    attributes of a query that must be used to match a reply. This flaw could be abused to perform a DNS Cache
    Poisoning attack. If chained with CVE-2020-25684 the attack complexity of a successful attack is reduced.
    The highest threat from this vulnerability is to data integrity. (CVE-2020-25685)

  - A flaw was found in dnsmasq before version 2.83. When receiving a query, dnsmasq does not check for an
    existing pending request for the same name and forwards a new request. By default, a maximum of 150
    pending queries can be sent to upstream servers, so there can be at most 150 queries for the same name.
    This flaw allows an off-path attacker on the network to substantially reduce the number of attempts that
    it would have to perform to forge a reply and have it accepted by dnsmasq. This issue is mentioned in the
    Birthday Attacks section of RFC5452. If chained with CVE-2020-25684, the attack complexity of a
    successful attack is reduced. The highest threat from this vulnerability is to data integrity.
    (CVE-2020-25686)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version
number.");
  script_set_attribute(attribute:"see_also", value:"https://alas.aws.amazon.com/AL2/ALAS-2021-1587.html");
  script_set_attribute(attribute:"see_also", value:"https://access.redhat.com/security/cve/CVE-2020-25684");
  script_set_attribute(attribute:"see_also", value:"https://access.redhat.com/security/cve/CVE-2020-25685");
  script_set_attribute(attribute:"see_also", value:"https://access.redhat.com/security/cve/CVE-2020-25686");
  script_set_attribute(attribute:"solution", value:
"Run 'yum update dnsmasq' to update your system.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:M/Au:N/C:N/I:P/A:N");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2020-25686");

  script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");

  script_set_attribute(attribute:"vuln_publication_date", value:"2021/01/19");
  script_set_attribute(attribute:"patch_publication_date", value:"2021/01/25");
  script_set_attribute(attribute:"plugin_publication_date", value:"2021/01/26");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:dnsmasq");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:dnsmasq-debuginfo");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:dnsmasq-utils");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:amazon:linux:2");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_family(english:"Amazon Linux Local Security Checks");

  script_copyright(english:"This script is Copyright (C) 2021-2022 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("ssh_get_info.nasl");
  script_require_keys("Host/local_checks_enabled", "Host/AmazonLinux/release", "Host/AmazonLinux/rpm-list");

  exit(0);
}

include("audit.inc");
include("global_settings.inc");
include("rpm.inc");

if (!get_kb_item("Host/local_checks_enabled")) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);

release = get_kb_item("Host/AmazonLinux/release");
if (isnull(release) || !strlen(release)) audit(AUDIT_OS_NOT, "Amazon Linux");
os_ver = pregmatch(pattern: "^AL(A|\d)", string:release);
if (isnull(os_ver)) audit(AUDIT_UNKNOWN_APP_VER, "Amazon Linux");
os_ver = os_ver[1];
if (os_ver != "2")
{
  if (os_ver == 'A') os_ver = 'AMI';
  audit(AUDIT_OS_NOT, "Amazon Linux 2", "Amazon Linux " + os_ver);
}

if (!get_kb_item("Host/AmazonLinux/rpm-list")) audit(AUDIT_PACKAGE_LIST_MISSING);

pkgs = [
    {'reference':'dnsmasq-2.76-16.amzn2.1.1', 'cpu':'aarch64', 'release':'AL2'},
    {'reference':'dnsmasq-2.76-16.amzn2.1.1', 'cpu':'i686', 'release':'AL2'},
    {'reference':'dnsmasq-2.76-16.amzn2.1.1', 'cpu':'x86_64', 'release':'AL2'},
    {'reference':'dnsmasq-debuginfo-2.76-16.amzn2.1.1', 'cpu':'aarch64', 'release':'AL2'},
    {'reference':'dnsmasq-debuginfo-2.76-16.amzn2.1.1', 'cpu':'i686', 'release':'AL2'},
    {'reference':'dnsmasq-debuginfo-2.76-16.amzn2.1.1', 'cpu':'x86_64', 'release':'AL2'},
    {'reference':'dnsmasq-utils-2.76-16.amzn2.1.1', 'cpu':'aarch64', 'release':'AL2'},
    {'reference':'dnsmasq-utils-2.76-16.amzn2.1.1', 'cpu':'i686', 'release':'AL2'},
    {'reference':'dnsmasq-utils-2.76-16.amzn2.1.1', 'cpu':'x86_64', 'release':'AL2'}
];

flag = 0;
foreach package_array ( pkgs ) {
  reference = NULL;
  release = NULL;
  cpu = NULL;
  el_string = NULL;
  rpm_spec_vers_cmp = NULL;
  allowmaj = NULL;
  if (!empty_or_null(package_array['reference'])) reference = package_array['reference'];
  if (!empty_or_null(package_array['release'])) release = package_array['release'];
  if (!empty_or_null(package_array['cpu'])) cpu = package_array['cpu'];
  if (!empty_or_null(package_array['el_string'])) el_string = package_array['el_string'];
  if (!empty_or_null(package_array['rpm_spec_vers_cmp'])) rpm_spec_vers_cmp = package_array['rpm_spec_vers_cmp'];
  if (!empty_or_null(package_array['allowmaj'])) allowmaj = package_array['allowmaj'];
  if (reference && release) {
    if (rpm_check(release:release, cpu:cpu, reference:reference, el_string:el_string, rpm_spec_vers_cmp:rpm_spec_vers_cmp, allowmaj:allowmaj)) flag++;
  }
}

if (flag)
{
  security_report_v4(
      port       : 0,
      severity   : SECURITY_WARNING,
      extra      : rpm_report_get()
  );
  exit(0);
}
else
{
  tested = pkg_tests_get();
  if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
  else audit(AUDIT_PACKAGE_NOT_INSTALLED, "dnsmasq / dnsmasq-debuginfo / dnsmasq-utils");
}