Amazon Linux 2 : amazon-cloudwatch-agent, --advisory ALAS2-2026-3844 (ALAS-2026-3844)

#%NASL_MIN_LEVEL 80900
##
# (C) Tenable, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Amazon Linux 2 Security Advisory ALAS-2026-3844.
##

include('compat.inc');

if (description)
{
  script_id(331987);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/08/04");

  script_cve_id(
    "CVE-2026-27145",
    "CVE-2026-39822",
    "CVE-2026-39827",
    "CVE-2026-39828",
    "CVE-2026-39832",
    "CVE-2026-39834",
    "CVE-2026-39835",
    "CVE-2026-42504",
    "CVE-2026-42505",
    "CVE-2026-42507",
    "CVE-2026-46597",
    "CVE-2026-46598"
  );
  script_xref(name:"IAVB", value:"2026-B-0120");
  script_xref(name:"IAVB", value:"2026-B-0146");
  script_xref(name:"IAVB", value:"2026-B-0193");

  script_name(english:"Amazon Linux 2 : amazon-cloudwatch-agent, --advisory ALAS2-2026-3844 (ALAS-2026-3844)");

  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 amazon-cloudwatch-agent installed on the remote host is prior to 1.300069.1-1. It is, therefore, affected
by multiple vulnerabilities as referenced in the ALAS2-2026-3844 advisory.

    (*x509.Certificate).VerifyHostname previously called matchHostnames in a loop over all DNS Subject
    Alternative Name (SAN) entries. This caused strings.Split(host, .) to execute repeatedly on the same
    input hostname. With a large DNS SAN list, verification costs scaled quadratically based on the number of
    SAN entries multiplied by the hostname's label count. Because x509.Verify validates hostnames before
    building the certificate chain, this overhead occurred even for untrusted certificates. (CVE-2026-27145)

    On Unix systems, opening a file in an os.Root improperly follows symlinks to locations outside of the Root
    when the final path component of the a path is a symbolic link and the path ends in /. For example,
    'root.Open(symlink/)' will open symlink even when symlink is a symbolic link pointing outside of the
    root. (CVE-2026-39822)

    An authenticated SSH client that repeatedly opened channels which were rejected by the server caused
    unbounded memory growth, eventually crashing the server process and affecting all connected users.
    Rejected channels are now properly removed from the connection's internal state and released for garbage
    collection. (CVE-2026-39827)

    When an SSH server authentication callback returned PartialSuccessError with non-nil Permissions, those
    permissions were silently discarded, potentially dropping certificate restrictions such as force-command
    after a second factor succeeded. Returning non-nil Permissions with PartialSuccessError now results in a
    connection error. (CVE-2026-39828)

    When adding a key to a remote agent constraint extensions such as [email protected]
    were not serialized in the request. Destination restrictions were silently stripped when forwarding keys,
    allowing unrestricted use of the key on the remote host. The client now serializes all constraint
    extensions. Additionally, the in-memory keyring returned by NewKeyring() now rejects keys with unsupported
    constraint extensions instead of silently ignoring them. (CVE-2026-39832)

    When writing data larger than 4GB in a single Write call on an SSH channel, an integer overflow in the
    internal payload size calculation caused the write loop to spin indefinitely, sending empty packets
    without making progress. The size comparison now uses int64 to prevent truncation. (CVE-2026-39834)

    SSH servers which use CertChecker as a public key callback without setting IsUserAuthority or
    IsHostAuthority could be caused to panic by a client presenting a certificate. CertChecker now returns an
    error instead of panicking when these callbacks are nil. (CVE-2026-39835)

    Decoding a maliciously-crafted MIME header containing many invalid encoded-words can consume excessive
    CPU. (CVE-2026-42504)

    Handshakes which used Encrypted Client Hello could be de-anonymized by a passive network observer due to a
    disclosure of pre-shared key identities in the unencrypted client hello. (CVE-2026-42505)

    When returning errors, functions in the net/textproto package would include its input as part of the
    error. This might allow an attacker to inject misleading content to errors that are printed or logged.
    (CVE-2026-42507)

    An incorrectly placed cast from bytes to int allowed for server-side panic in the AES-GCM packet decoder
    for well-crafted inputs. (CVE-2026-46597)

    For certain crafted inputs, a 'ed25519.PrivateKey' was created by casting malformed wire bytes, leading to
    a panic when used. (CVE-2026-46598)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues 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/ALAS2-2026-3844.html");
  script_set_attribute(attribute:"see_also", value:"https://alas.aws.amazon.com/faqs.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-27145.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-39822.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-39827.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-39828.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-39832.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-39834.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-39835.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-42504.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-42505.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-42507.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-46597.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-46598.html");
  script_set_attribute(attribute:"solution", value:
"Run 'yum update amazon-cloudwatch-agent' or
  or 'yum update --advisory ALAS2-2026-3844' to update your system.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:N/I:C/A:C");
  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:H/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2026-39834");

  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:"2026/05/12");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/08/04");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/08/04");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:amazon-cloudwatch-agent");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:amazon:linux:2");
  script_set_attribute(attribute:"generated_plugin", value:"current");
  script_set_attribute(attribute:"stig_severity", value:"I");
  script_end_attributes();

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

  script_copyright(english:"This script is Copyright (C) 2026 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("rpm2.inc");

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

var alas_release = get_kb_item("Host/AmazonLinux/release");
if (isnull(alas_release) || !strlen(alas_release)) audit(AUDIT_OS_NOT, "Amazon Linux");
var os_ver = pregmatch(pattern: "^AL(A|\d+|-\d+)", string:alas_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);

var pkgs = [
    {'reference':'amazon-cloudwatch-agent-1.300069.1-1.amzn2', 'cpu':'aarch64', 'release':'AL2', 'rpm_spec_vers_cmp':TRUE},
    {'reference':'amazon-cloudwatch-agent-1.300069.1-1.amzn2', 'cpu':'x86_64', 'release':'AL2', 'rpm_spec_vers_cmp':TRUE}
];

var flag = 0;
foreach var package_array ( pkgs ) {
  var reference = NULL;
  var _release = NULL;
  var sp = NULL;
  var _cpu = NULL;
  var el_string = NULL;
  var rpm_spec_vers_cmp = NULL;
  var epoch = NULL;
  var allowmaj = NULL;
  var exists_check = NULL;
  var cves = 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['sp'])) sp = package_array['sp'];
  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['epoch'])) epoch = package_array['epoch'];
  if (!empty_or_null(package_array['allowmaj'])) allowmaj = package_array['allowmaj'];
  if (!empty_or_null(package_array['exists_check'])) exists_check = package_array['exists_check'];
  if (!empty_or_null(package_array['cves'])) cves = package_array['cves'];
  if (reference && _release && (!exists_check || rpm_exists(release:_release, rpm:exists_check))) {
    if (rpm_check(release:_release, sp:sp, cpu:_cpu, reference:reference, epoch:epoch, el_string:el_string, rpm_spec_vers_cmp:rpm_spec_vers_cmp, allowmaj:allowmaj, cves:cves)) flag++;
  }
}

if (flag)
{
  security_report_v4(
      port       : 0,
      severity   : SECURITY_HOLE,
      extra      : rpm_report_get()
  );
  exit(0);
}
else
{
  var tested = pkg_tests_get();
  if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
  else audit(AUDIT_PACKAGE_NOT_INSTALLED, "amazon-cloudwatch-agent");
}