Debian DSA-2826-1 : denyhosts - remote denial of ssh service

2013-12-23T00:00:00
ID DEBIAN_DSA-2826.NASL
Type nessus
Reporter Tenable
Modified 2018-07-09T00:00:00

Description

Helmut Grohne discovered that denyhosts, a tool preventing SSH brute-force attacks, could be used to perform remote denial of service against the SSH daemon. Incorrectly specified regular expressions used to detect brute-force attacks in authentication logs could be exploited by a malicious user to forge crafted login names in order to make denyhosts ban arbitrary IP addresses.

                                        
                                            #
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were  
# extracted from Debian Security Advisory DSA-2826. The text 
# itself is copyright (C) Software in the Public Interest, Inc.
#

include("compat.inc");

if (description)
{
  script_id(71586);
  script_version("1.6");
  script_cvs_date("Date: 2018/07/09 14:30:25");

  script_cve_id("CVE-2013-6890");
  script_bugtraq_id(64478);
  script_xref(name:"DSA", value:"2826");

  script_name(english:"Debian DSA-2826-1 : denyhosts - remote denial of ssh service");
  script_summary(english:"Checks dpkg output for the updated package");

  script_set_attribute(
    attribute:"synopsis", 
    value:"The remote Debian host is missing a security-related update."
  );
  script_set_attribute(
    attribute:"description", 
    value:
"Helmut Grohne discovered that denyhosts, a tool preventing SSH
brute-force attacks, could be used to perform remote denial of service
against the SSH daemon. Incorrectly specified regular expressions used
to detect brute-force attacks in authentication logs could be
exploited by a malicious user to forge crafted login names in order to
make denyhosts ban arbitrary IP addresses."
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://packages.debian.org/source/squeeze/denyhosts"
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://packages.debian.org/source/wheezy/denyhosts"
  );
  script_set_attribute(
    attribute:"see_also",
    value:"http://www.debian.org/security/2013/dsa-2826"
  );
  script_set_attribute(
    attribute:"solution", 
    value:
"Upgrade the denyhosts packages.

For the oldstable distribution (squeeze), this problem has been fixed
in version 2.6-7+deb6u2.

For the stable distribution (wheezy), this problem has been fixed in
version 2.6-10+deb7u2."
  );
  script_set_cvss_base_vector("CVSS2#AV:N/AC:L/Au:N/C:N/I:N/A:P");
  script_set_cvss_temporal_vector("CVSS2#E:POC/RL:OF/RC:C");
  script_set_attribute(attribute:"exploitability_ease", value:"Exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"true");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:debian:debian_linux:denyhosts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:6.0");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:debian:debian_linux:7.0");

  script_set_attribute(attribute:"patch_publication_date", value:"2013/12/22");
  script_set_attribute(attribute:"plugin_publication_date", value:"2013/12/23");
  script_set_attribute(attribute:"vuln_publication_date", value:"2006/12/04");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_copyright(english:"This script is Copyright (C) 2013-2018 Tenable Network Security, Inc.");
  script_family(english:"Debian Local Security Checks");

  script_dependencies("ssh_get_info.nasl");
  script_require_keys("Host/local_checks_enabled", "Host/Debian/release", "Host/Debian/dpkg-l");

  exit(0);
}


include("audit.inc");
include("debian_package.inc");


if (!get_kb_item("Host/local_checks_enabled")) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
if (!get_kb_item("Host/Debian/release")) audit(AUDIT_OS_NOT, "Debian");
if (!get_kb_item("Host/Debian/dpkg-l")) audit(AUDIT_PACKAGE_LIST_MISSING);


flag = 0;
if (deb_check(release:"6.0", prefix:"denyhosts", reference:"2.6-7+deb6u2")) flag++;
if (deb_check(release:"7.0", prefix:"denyhosts", reference:"2.6-10+deb7u2")) flag++;

if (flag)
{
  if (report_verbosity > 0) security_warning(port:0, extra:deb_report_get());
  else security_warning(0);
  exit(0);
}
else audit(AUDIT_HOST_NOT, "affected");