Amazon Linux 2 : python-pyasn1, --advisory ALAS2-2026-3836 (ALAS-2026-3836)

#%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-2026-3836.
##

include('compat.inc');

if (description)
{
  script_id(332047);
  script_version("1.1");
  script_set_attribute(attribute:"plugin_modification_date", value:"2026/08/04");

  script_cve_id("CVE-2026-59884", "CVE-2026-59885", "CVE-2026-59886");

  script_name(english:"Amazon Linux 2 : python-pyasn1, --advisory ALAS2-2026-3836 (ALAS-2026-3836)");

  script_set_attribute(attribute:"synopsis", value:
"The remote Amazon Linux 2 host is missing a security update.");
  script_set_attribute(attribute:"description", value:
"It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2-2026-3836 advisory.

    pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the BER decoder shared by the CER and DER
    codecs parses long-form tags by accumulating continuation octets without an upper bound on the tag ID
    size, allowing a crafted input to force construction of an arbitrarily large integer with CPU cost growing
    quadratically and to trigger unhandled ValueError exceptions in Python 3.11+ error formatting paths. Any
    application decoding untrusted BER, CER, or DER input is affected. This issue is fixed in version 0.6.4.
    (CVE-2026-59884)

    pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the BER, CER, and DER decoders process
    OBJECT IDENTIFIER and RELATIVE-OID values in quadratic time relative to the number of arcs, so a small
    crafted payload containing an OID with many arcs consumes excessive CPU per decode() call and can deny
    service to applications that decode untrusted ASN.1 data. The corresponding encoders have the same
    quadratic behavior when an application re-encodes previously decoded attacker-supplied values. This issue
    is fixed in version 0.6.4. (CVE-2026-59885)

    pyasn1 is a generic ASN.1 library for Python. Prior to 0.6.4, the univ.Real type converted its mantissa,
    base, and exponent value to a Python float using exact big-integer exponentiation. A BER, CER, or DER
    encoded REAL value only a few bytes long can carry a very large exponent, causing float conversion through
    prettyPrint(), str(), comparison, arithmetic, int(), or an explicit float() call to consume excessive CPU
    and memory and hang applications that decode untrusted ASN.1 data and then print, log, or compare decoded
    objects. This issue is fixed in version 0.6.4. (CVE-2026-59886)

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/ALAS2-2026-3836.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-2026-59884.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-59885.html");
  script_set_attribute(attribute:"see_also", value:"https://explore.alas.aws.amazon.com/CVE-2026-59886.html");
  script_set_attribute(attribute:"solution", value:
"Run 'yum update python-pyasn1' or
  or 'yum update --advisory ALAS2-2026-3836' to update your system.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:N/I:N/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:N/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-2026-59886");

  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:"2026/07/14");
  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:python2-pyasn1");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:python2-pyasn1-modules");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:python3-pyasn1");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:python3-pyasn1-modules");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:amazon:linux:2");
  script_set_attribute(attribute:"generated_plugin", value:"current");
  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':'python2-pyasn1-0.1.9-7.amzn2.0.5', 'release':'AL2', 'rpm_spec_vers_cmp':TRUE},
    {'reference':'python2-pyasn1-modules-0.1.9-7.amzn2.0.5', 'release':'AL2', 'rpm_spec_vers_cmp':TRUE},
    {'reference':'python3-pyasn1-0.1.9-7.amzn2.0.5', 'release':'AL2', 'rpm_spec_vers_cmp':TRUE},
    {'reference':'python3-pyasn1-modules-0.1.9-7.amzn2.0.5', '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, "python2-pyasn1 / python2-pyasn1-modules / python3-pyasn1 / etc");
}