Amazon Linux 2 : amazon-ssm-agent, --advisory ALAS2-2026-3809 (ALAS-2026-3809)

#%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-2026-3809.
##

include('compat.inc');

if (description)
{
  script_id(328842);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/07/21");

  script_cve_id(
    "CVE-2026-39827",
    "CVE-2026-39829",
    "CVE-2026-39830",
    "CVE-2026-39831",
    "CVE-2026-39834",
    "CVE-2026-39835",
    "CVE-2026-41506",
    "CVE-2026-42508",
    "CVE-2026-46597"
  );
  script_xref(name:"IAVB", value:"2026-B-0120");

  script_name(english:"Amazon Linux 2 : amazon-ssm-agent, --advisory ALAS2-2026-3809 (ALAS-2026-3809)");

  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-ssm-agent installed on the remote host is prior to 3.3.4624.0-1. It is, therefore, affected by
multiple vulnerabilities as referenced in the ALAS2-2026-3809 advisory.

    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)

    The RSA and DSA public key parsers did not enforce size limits on key parameters. A crafted public key
    with an excessively large modulus or DSA parameter could cause several minutes of CPU consumption during
    signature verification. This could be triggered by unauthenticated clients during public key
    authentication. RSA moduli are now limited to 8192 bits, and DSA parameters are validated per FIPS 186-2.
    (CVE-2026-39829)

    A malicious SSH peer could send unsolicited global request responses to fill an internal buffer, blocking
    the connection's read loop. The blocked goroutine could not be released by calling Close(), resulting in a
    resource leak per connection. Unsolicited global responses are now discarded. (CVE-2026-39830)

    The Verify() method for FIDO/U2F security key types ([email protected], sk-ssh-
    [email protected]) did not check the User Presence flag. Signatures generated without physical touch
    were accepted, allowing unattended use of a hardware security key. To restore the previous behavior,
    return a no-touch-required extension in Permissions.Extensions from PublicKeyCallback. (CVE-2026-39831)

    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)

    go-git is an extensible git implementation library written in pure Go. Prior to versions 5.18.0 and
    6.0.0-alpha.2, go-git may leak HTTP authentication credentials when following redirects during smart-HTTP
    clone and fetch operations. This issue has been patched in versions 5.18.0 and 6.0.0-alpha.2.
    (CVE-2026-41506)

    Previously, a revoked 'SignatureKey' belonging to a CA was not correctly checked for revocation. Now, both
    the 'key' and 'key.SignatureKey' are checked for @revoked. (CVE-2026-42508)

    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)

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/ALAS2-2026-3809.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-2026-39827.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-39829.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-39830.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-39831.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-2026-41506.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-42508.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-46597.html");
  script_set_attribute(attribute:"solution", value:
"Run 'yum update amazon-ssm-agent' or
  or 'yum update --advisory ALAS2-2026-3809' to update your system.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:C/I:N/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:L/PR:N/UI:R/S:C/C:H/I:N/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-2026-41506");

  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:"2026/04/17");
  script_set_attribute(attribute:"patch_publication_date", value:"2026/07/20");
  script_set_attribute(attribute:"plugin_publication_date", value:"2026/07/21");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:amazon-ssm-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-ssm-agent-3.3.4624.0-1.amzn2', 'cpu':'aarch64', 'release':'AL2', 'rpm_spec_vers_cmp':TRUE},
    {'reference':'amazon-ssm-agent-3.3.4624.0-1.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-ssm-agent");
}