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nessusThis script is Copyright (C) 2021-2024 and is owned by Tenable, Inc. or an Affiliate thereof.ALA_ALAS-2021-1492.NASL
HistoryApr 07, 2021 - 12:00 a.m.

Amazon Linux AMI : screen (ALAS-2021-1492)

2021-04-0700:00:00
This script is Copyright (C) 2021-2024 and is owned by Tenable, Inc. or an Affiliate thereof.
www.tenable.com
38

CVSS2

7.5

Attack Vector

NETWORK

Attack Complexity

LOW

Authentication

NONE

Confidentiality Impact

PARTIAL

Integrity Impact

PARTIAL

Availability Impact

PARTIAL

AV:N/AC:L/Au:N/C:P/I:P/A:P

CVSS3

9.8

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

AI Score

9.8

Confidence

High

EPSS

0.015

Percentile

86.7%

The version of screen installed on the remote host is prior to 4.0.3-19.7. It is, therefore, affected by a vulnerability as referenced in the ALAS-2021-1492 advisory.

  • encoding.c in GNU Screen through 4.8.0 allows remote attackers to cause a denial of service (invalid write access and application crash) or possibly have unspecified other impact via a crafted UTF-8 character sequence. (CVE-2021-26937)

Note that Nessus has not tested for this issue but has instead relied only on the application’s self-reported version number.

##
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Amazon Linux AMI Security Advisory ALAS-2021-1492.
##

include('compat.inc');

if (description)
{
  script_id(148377);
  script_version("1.3");
  script_set_attribute(attribute:"plugin_modification_date", value:"2024/01/05");

  script_cve_id("CVE-2021-26937");
  script_xref(name:"ALAS", value:"2021-1492");

  script_name(english:"Amazon Linux AMI : screen (ALAS-2021-1492)");

  script_set_attribute(attribute:"synopsis", value:
"The remote Amazon Linux AMI host is missing a security update.");
  script_set_attribute(attribute:"description", value:
"The version of screen installed on the remote host is prior to 4.0.3-19.7. It is, therefore, affected by a vulnerability
as referenced in the ALAS-2021-1492 advisory.

  - encoding.c in GNU Screen through 4.8.0 allows remote attackers to cause a denial of service (invalid write
    access and application crash) or possibly have unspecified other impact via a crafted UTF-8 character
    sequence. (CVE-2021-26937)

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/ALAS-2021-1492.html");
  script_set_attribute(attribute:"see_also", value:"https://access.redhat.com/security/cve/CVE-2021-26937");
  script_set_attribute(attribute:"solution", value:
"Run 'yum update screen' to update your system.");
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:P");
  script_set_cvss_temporal_vector("CVSS2#E:POC/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:P/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2021-26937");

  script_set_attribute(attribute:"exploitability_ease", value:"Exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"true");

  script_set_attribute(attribute:"vuln_publication_date", value:"2021/02/09");
  script_set_attribute(attribute:"patch_publication_date", value:"2021/04/07");
  script_set_attribute(attribute:"plugin_publication_date", value:"2021/04/07");

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

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

  script_copyright(english:"This script is Copyright (C) 2021-2024 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 != "A")
{
  if (os_ver == 'A') os_ver = 'AMI';
  audit(AUDIT_OS_NOT, "Amazon Linux AMI", "Amazon Linux " + os_ver);
}

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

pkgs = [
    {'reference':'screen-4.0.3-19.7.amzn1', 'cpu':'i686', 'release':'ALA', 'rpm_spec_vers_cmp':TRUE},
    {'reference':'screen-4.0.3-19.7.amzn1', 'cpu':'x86_64', 'release':'ALA', 'rpm_spec_vers_cmp':TRUE},
    {'reference':'screen-debuginfo-4.0.3-19.7.amzn1', 'cpu':'i686', 'release':'ALA', 'rpm_spec_vers_cmp':TRUE},
    {'reference':'screen-debuginfo-4.0.3-19.7.amzn1', 'cpu':'x86_64', 'release':'ALA', 'rpm_spec_vers_cmp':TRUE}
];

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_HOLE,
      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, "screen / screen-debuginfo");
}
VendorProductVersionCPE
amazonlinuxscreenp-cpe:/a:amazon:linux:screen
amazonlinuxscreen-debuginfop-cpe:/a:amazon:linux:screen-debuginfo
amazonlinuxcpe:/o:amazon:linux

CVSS2

7.5

Attack Vector

NETWORK

Attack Complexity

LOW

Authentication

NONE

Confidentiality Impact

PARTIAL

Integrity Impact

PARTIAL

Availability Impact

PARTIAL

AV:N/AC:L/Au:N/C:P/I:P/A:P

CVSS3

9.8

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality Impact

HIGH

Integrity Impact

HIGH

Availability Impact

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

AI Score

9.8

Confidence

High

EPSS

0.015

Percentile

86.7%