The symmetric-key feature in the receive function in ntp_proto.c in ntpd in NTP 4.x before 4.2.8p2 requires a correct MAC only if the MAC field has a nonzero length, which makes it easier for man-in-the-middle attackers to spoof packets by omitting the MAC.
(CVE-2015-1798)
The symmetric-key feature in the receive function in ntp_proto.c in ntpd in NTP 3.x and 4.x before 4.2.8p2 performs state-variable updates upon receiving certain invalid packets, which makes it easier for man-in-the-middle attackers to cause a denial of service (synchronization loss) by spoofing the source IP address of a peer.
(CVE-2015-1799)
This update also addresses leap-second handling. With older ntp versions, the -x option was sometimes used as a workaround to avoid kernel inserting/deleting leap seconds by stepping the clock and possibly upsetting running applications. That no longer works with 4.2.6 as ntpd steps the clock itself when a leap second occurs. The fix is to treat the one second offset gained during leap second as a normal offset and check the stepping threshold (set by -x or tinker step) to decide if a step should be applied. See this forum post for more information on the Amazon Linux AMI’s leap-second handling.
#
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Amazon Linux AMI Security Advisory ALAS-2015-520.
#
include("compat.inc");
if (description)
{
script_id(83271);
script_version("1.3");
script_cvs_date("Date: 2018/04/18 15:09:35");
script_cve_id("CVE-2015-1798", "CVE-2015-1799");
script_xref(name:"ALAS", value:"2015-520");
script_name(english:"Amazon Linux AMI : ntp (ALAS-2015-520)");
script_summary(english:"Checks rpm output for the updated packages");
script_set_attribute(
attribute:"synopsis",
value:"The remote Amazon Linux AMI host is missing a security update."
);
script_set_attribute(
attribute:"description",
value:
"The symmetric-key feature in the receive function in ntp_proto.c in
ntpd in NTP 4.x before 4.2.8p2 requires a correct MAC only if the MAC
field has a nonzero length, which makes it easier for
man-in-the-middle attackers to spoof packets by omitting the MAC.
(CVE-2015-1798)
The symmetric-key feature in the receive function in ntp_proto.c in
ntpd in NTP 3.x and 4.x before 4.2.8p2 performs state-variable updates
upon receiving certain invalid packets, which makes it easier for
man-in-the-middle attackers to cause a denial of service
(synchronization loss) by spoofing the source IP address of a peer.
(CVE-2015-1799)
This update also addresses leap-second handling. With older ntp
versions, the -x option was sometimes used as a workaround to avoid
kernel inserting/deleting leap seconds by stepping the clock and
possibly upsetting running applications. That no longer works with
4.2.6 as ntpd steps the clock itself when a leap second occurs. The
fix is to treat the one second offset gained during leap second as a
normal offset and check the stepping threshold (set by -x or tinker
step) to decide if a step should be applied. See this forum post for
more information on the Amazon Linux AMI's leap-second handling."
);
script_set_attribute(
attribute:"see_also",
value:"https://bugzilla.redhat.com/show_bug.cgi?id=1196635"
);
script_set_attribute(
attribute:"see_also",
value:"https://forums.aws.amazon.com/ann.jspa?annID=3064"
);
script_set_attribute(
attribute:"see_also",
value:"https://alas.aws.amazon.com/ALAS-2015-520.html"
);
script_set_attribute(
attribute:"solution",
value:"Run 'yum update ntp' to update your system."
);
script_set_cvss_base_vector("CVSS2#AV:A/AC:M/Au:N/C:N/I:P/A:P");
script_set_attribute(attribute:"plugin_type", value:"local");
script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:ntp");
script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:ntp-debuginfo");
script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:ntp-doc");
script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:ntp-perl");
script_set_attribute(attribute:"cpe", value:"p-cpe:/a:amazon:linux:ntpdate");
script_set_attribute(attribute:"cpe", value:"cpe:/o:amazon:linux");
script_set_attribute(attribute:"patch_publication_date", value:"2015/05/05");
script_set_attribute(attribute:"plugin_publication_date", value:"2015/05/07");
script_end_attributes();
script_category(ACT_GATHER_INFO);
script_copyright(english:"This script is Copyright (C) 2015-2018 Tenable Network Security, Inc.");
script_family(english:"Amazon Linux Local Security Checks");
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);
flag = 0;
if (rpm_check(release:"ALA", reference:"ntp-4.2.6p5-30.24.amzn1")) flag++;
if (rpm_check(release:"ALA", reference:"ntp-debuginfo-4.2.6p5-30.24.amzn1")) flag++;
if (rpm_check(release:"ALA", reference:"ntp-doc-4.2.6p5-30.24.amzn1")) flag++;
if (rpm_check(release:"ALA", reference:"ntp-perl-4.2.6p5-30.24.amzn1")) flag++;
if (rpm_check(release:"ALA", reference:"ntpdate-4.2.6p5-30.24.amzn1")) flag++;
if (flag)
{
if (report_verbosity > 0) security_warning(port:0, extra:rpm_report_get());
else security_warning(0);
exit(0);
}
else
{
tested = pkg_tests_get();
if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
else audit(AUDIT_PACKAGE_NOT_INSTALLED, "ntp / ntp-debuginfo / ntp-doc / ntp-perl / ntpdate");
}