Vulnerabilities > CVE-2013-6890 - Improper Authentication vulnerability in multiple products

047910
CVSS 0.0 - NONE
Attack vector
UNKNOWN
Attack complexity
UNKNOWN
Privileges required
UNKNOWN
Confidentiality impact
UNKNOWN
Integrity impact
UNKNOWN
Availability impact
UNKNOWN
debian
fedoraproject
phil-schwartz
CWE-287
nessus
exploit available
NVD
Published: 2013-12-23
Updated: 2024-11-21

Summary

denyhosts 2.6 uses an incorrect regular expression when analyzing authentication logs, which allows remote attackers to cause a denial of service (incorrect block of IP addresses) via crafted login names.

Vulnerable Configurations

Part Description Count
OS
Debian
3
OS
Fedoraproject
1
Application
Phil_Schwartz
1

Common Weakness Enumeration (CWE)

Common Attack Pattern Enumeration and Classification (CAPEC)

  • Authentication Abuse
    An attacker obtains unauthorized access to an application, service or device either through knowledge of the inherent weaknesses of an authentication mechanism, or by exploiting a flaw in the authentication scheme's implementation. In such an attack an authentication mechanism is functioning but a carefully controlled sequence of events causes the mechanism to grant access to the attacker. This attack may exploit assumptions made by the target's authentication procedures, such as assumptions regarding trust relationships or assumptions regarding the generation of secret values. This attack differs from Authentication Bypass attacks in that Authentication Abuse allows the attacker to be certified as a valid user through illegitimate means, while Authentication Bypass allows the user to access protected material without ever being certified as an authenticated user. This attack does not rely on prior sessions established by successfully authenticating users, as relied upon for the "Exploitation of Session Variables, Resource IDs and other Trusted Credentials" attack patterns.
  • Exploiting Trust in Client (aka Make the Client Invisible)
    An attack of this type exploits a programs' vulnerabilities in client/server communication channel authentication and data integrity. It leverages the implicit trust a server places in the client, or more importantly, that which the server believes is the client. An attacker executes this type of attack by placing themselves in the communication channel between client and server such that communication directly to the server is possible where the server believes it is communicating only with a valid client. There are numerous variations of this type of attack.
  • Utilizing REST's Trust in the System Resource to Register Man in the Middle
    This attack utilizes a REST(REpresentational State Transfer)-style applications' trust in the system resources and environment to place man in the middle once SSL is terminated. Rest applications premise is that they leverage existing infrastructure to deliver web services functionality. An example of this is a Rest application that uses HTTP Get methods and receives a HTTP response with an XML document. These Rest style web services are deployed on existing infrastructure such as Apache and IIS web servers with no SOAP stack required. Unfortunately from a security standpoint, there frequently is no interoperable identity security mechanism deployed, so Rest developers often fall back to SSL to deliver security. In large data centers, SSL is typically terminated at the edge of the network - at the firewall, load balancer, or router. Once the SSL is terminated the HTTP request is in the clear (unless developers have hashed or encrypted the values, but this is rare). The attacker can utilize a sniffer such as Wireshark to snapshot the credentials, such as username and password that are passed in the clear once SSL is terminated. Once the attacker gathers these credentials, they can submit requests to the web service provider just as authorized user do. There is not typically an authentication on the client side, beyond what is passed in the request itself so once this is compromised, then this is generally sufficient to compromise the service's authentication scheme.
  • Man in the Middle Attack
    This type of attack targets the communication between two components (typically client and server). The attacker places himself in the communication channel between the two components. Whenever one component attempts to communicate with the other (data flow, authentication challenges, etc.), the data first goes to the attacker, who has the opportunity to observe or alter it, and it is then passed on to the other component as if it was never intercepted. This interposition is transparent leaving the two compromised components unaware of the potential corruption or leakage of their communications. The potential for Man-in-the-Middle attacks yields an implicit lack of trust in communication or identify between two components.

Exploit-Db

descriptionDenyHosts 'regex.py' Remote Denial of Service Vulnerability. CVE-2013-6890. Dos exploit for linux platform
idEDB-ID:38909
last seen2016-02-04
modified2013-12-19
published2013-12-19
reporterHelmut Grohne
sourcehttps://www.exploit-db.com/download/38909/
titleDenyHosts 'regex.py' Remote Denial of Service Vulnerability

Nessus

  • NASL familyFedora Local Security Checks
    NASL idFEDORA_2014-17081.NASL
    descriptionFix security bug Note that Tenable Network Security has extracted the preceding description block directly from the Fedora security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.
    last seen2020-03-17
    modified2015-01-06
    plugin id80372
    published2015-01-06
    reporterThis script is Copyright (C) 2015-2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/80372
    titleFedora 19 : denyhosts-2.6-28.fc19.1 (2014-17081)
    code
    #%NASL_MIN_LEVEL 80502
#
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were  
# extracted from Fedora Security Advisory 2014-17081.
#

include("compat.inc");

if (description)
{
  script_id(80372);
  script_version("1.5");
  script_set_attribute(attribute:"plugin_modification_date", value:"2020/03/12");

  script_cve_id("CVE-2013-6890");
  script_bugtraq_id(64478);
  script_xref(name:"FEDORA", value:"2014-17081");

  script_name(english:"Fedora 19 : denyhosts-2.6-28.fc19.1 (2014-17081)");
  script_summary(english:"Checks rpm output for the updated package.");

  script_set_attribute(
    attribute:"synopsis", 
    value:"The remote Fedora host is missing a security update."
  );
  script_set_attribute(
    attribute:"description", 
    value:
"Fix security bug

Note that Tenable Network Security has extracted the preceding
description block directly from the Fedora security advisory. Tenable
has attempted to automatically clean and format it as much as possible
without introducing additional issues."
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://bugzilla.redhat.com/show_bug.cgi?id=1045982"
  );
  # https://lists.fedoraproject.org/pipermail/package-announce/2015-January/147499.html
  script_set_attribute(
    attribute:"see_also",
    value:"http://www.nessus.org/u?91aea18d"
  );
  script_set_attribute(
    attribute:"solution", 
    value:"Update the affected denyhosts package."
  );
  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:fedoraproject:fedora:denyhosts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:fedoraproject:fedora:19");

  script_set_attribute(attribute:"patch_publication_date", value:"2014/12/16");
  script_set_attribute(attribute:"plugin_publication_date", value:"2015/01/06");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_copyright(english:"This script is Copyright (C) 2015-2020 and is owned by Tenable, Inc. or an Affiliate thereof.");
  script_family(english:"Fedora Local Security Checks");

  script_dependencies("ssh_get_info.nasl");
  script_require_keys("Host/local_checks_enabled", "Host/RedHat/release", "Host/RedHat/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/RedHat/release");
if (isnull(release) || "Fedora" >!< release) audit(AUDIT_OS_NOT, "Fedora");
os_ver = eregmatch(pattern: "Fedora.*release ([0-9]+)", string:release);
if (isnull(os_ver)) audit(AUDIT_UNKNOWN_APP_VER, "Fedora");
os_ver = os_ver[1];
if (! ereg(pattern:"^19([^0-9]|$)", string:os_ver)) audit(AUDIT_OS_NOT, "Fedora 19.x", "Fedora " + os_ver);

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

cpu = get_kb_item("Host/cpu");
if (isnull(cpu)) audit(AUDIT_UNKNOWN_ARCH);
if ("x86_64" >!< cpu && cpu !~ "^i[3-6]86$") audit(AUDIT_LOCAL_CHECKS_NOT_IMPLEMENTED, "Fedora", cpu);

flag = 0;
if (rpm_check(release:"FC19", reference:"denyhosts-2.6-28.fc19.1")) 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, "denyhosts");
}
  • NASL familyGentoo Local Security Checks
    NASL idGENTOO_GLSA-201406-23.NASL
    descriptionThe remote host is affected by the vulnerability described in GLSA-201406-23 (DenyHosts: Denial of Service) DenyHosts does not properly define the regular expressions used when parsing SSH authentication logs. Impact : A remote attacker could possibly cause a Denial of Service condition via a crafted login name. Workaround : There is no known workaround at this time.
    last seen2020-06-01
    modified2020-06-02
    plugin id76225
    published2014-06-26
    reporterThis script is Copyright (C) 2014-2018 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/76225
    titleGLSA-201406-23 : DenyHosts: Denial of Service
    code
    #
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from Gentoo Linux Security Advisory GLSA 201406-23.
#
# The advisory text is Copyright (C) 2001-2015 Gentoo Foundation, Inc.
# and licensed under the Creative Commons - Attribution / Share Alike 
# license. See http://creativecommons.org/licenses/by-sa/3.0/
#

include("compat.inc");

if (description)
{
  script_id(76225);
  script_version("1.4");
  script_cvs_date("Date: 2018/12/05 20:31:22");

  script_cve_id("CVE-2013-6890");
  script_bugtraq_id(64478);
  script_xref(name:"GLSA", value:"201406-23");

  script_name(english:"GLSA-201406-23 : DenyHosts: Denial of Service");
  script_summary(english:"Checks for updated package(s) in /var/db/pkg");

  script_set_attribute(
    attribute:"synopsis", 
    value:
"The remote Gentoo host is missing one or more security-related
patches."
  );
  script_set_attribute(
    attribute:"description", 
    value:
"The remote host is affected by the vulnerability described in GLSA-201406-23
(DenyHosts: Denial of Service)

    DenyHosts does not properly define the regular expressions used when
      parsing SSH authentication logs.
  
Impact :

    A remote attacker could possibly cause a Denial of Service condition via
      a crafted login name.
  
Workaround :

    There is no known workaround at this time."
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://security.gentoo.org/glsa/201406-23"
  );
  script_set_attribute(
    attribute:"solution", 
    value:
"All DenyHost users should upgrade to the latest version:
      # emerge --sync
      # emerge --ask --oneshot --verbose '>=app-admin/denyhosts-2.6-r9'"
  );
  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:gentoo:linux:denyhosts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:gentoo:linux");

  script_set_attribute(attribute:"patch_publication_date", value:"2014/06/25");
  script_set_attribute(attribute:"plugin_publication_date", value:"2014/06/26");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_copyright(english:"This script is Copyright (C) 2014-2018 and is owned by Tenable, Inc. or an Affiliate thereof.");
  script_family(english:"Gentoo Local Security Checks");

  script_dependencies("ssh_get_info.nasl");
  script_require_keys("Host/local_checks_enabled", "Host/Gentoo/release", "Host/Gentoo/qpkg-list");

  exit(0);
}


include("audit.inc");
include("global_settings.inc");
include("qpkg.inc");

if (!get_kb_item("Host/local_checks_enabled")) audit(AUDIT_LOCAL_CHECKS_NOT_ENABLED);
if (!get_kb_item("Host/Gentoo/release")) audit(AUDIT_OS_NOT, "Gentoo");
if (!get_kb_item("Host/Gentoo/qpkg-list")) audit(AUDIT_PACKAGE_LIST_MISSING);


flag = 0;

if (qpkg_check(package:"app-admin/denyhosts", unaffected:make_list("ge 2.6-r9"), vulnerable:make_list("lt 2.6-r9"))) flag++;

if (flag)
{
  if (report_verbosity > 0) security_warning(port:0, extra:qpkg_report_get());
  else security_warning(0);
  exit(0);
}
else
{
  tested = qpkg_tests_get();
  if (tested) audit(AUDIT_PACKAGE_NOT_AFFECTED, tested);
  else audit(AUDIT_PACKAGE_NOT_INSTALLED, "DenyHosts");
}
  • NASL familyDebian Local Security Checks
    NASL idDEBIAN_DSA-2826.NASL
    descriptionHelmut 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.
    last seen2020-03-17
    modified2013-12-23
    plugin id71586
    published2013-12-23
    reporterThis script is Copyright (C) 2013-2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/71586
    titleDebian DSA-2826-1 : denyhosts - remote denial of ssh service
    code
    #%NASL_MIN_LEVEL 80502
#
# (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("1.8");
  script_set_attribute(attribute:"plugin_modification_date", value:"2020/03/12");

  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:"https://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_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_copyright(english:"This script is Copyright (C) 2013-2020 and is owned by Tenable, Inc. or an Affiliate thereof.");
  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");
  • NASL familyFedora Local Security Checks
    NASL idFEDORA_2014-17067.NASL
    descriptionFix security bug Note that Tenable Network Security has extracted the preceding description block directly from the Fedora security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.
    last seen2020-03-17
    modified2015-01-06
    plugin id80371
    published2015-01-06
    reporterThis script is Copyright (C) 2015-2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/80371
    titleFedora 20 : denyhosts-2.6-29.fc20.1 (2014-17067)
    code
    #%NASL_MIN_LEVEL 80502
#
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were  
# extracted from Fedora Security Advisory 2014-17067.
#

include("compat.inc");

if (description)
{
  script_id(80371);
  script_version("1.5");
  script_set_attribute(attribute:"plugin_modification_date", value:"2020/03/12");

  script_cve_id("CVE-2013-6890");
  script_bugtraq_id(64478);
  script_xref(name:"FEDORA", value:"2014-17067");

  script_name(english:"Fedora 20 : denyhosts-2.6-29.fc20.1 (2014-17067)");
  script_summary(english:"Checks rpm output for the updated package.");

  script_set_attribute(
    attribute:"synopsis", 
    value:"The remote Fedora host is missing a security update."
  );
  script_set_attribute(
    attribute:"description", 
    value:
"Fix security bug

Note that Tenable Network Security has extracted the preceding
description block directly from the Fedora security advisory. Tenable
has attempted to automatically clean and format it as much as possible
without introducing additional issues."
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://bugzilla.redhat.com/show_bug.cgi?id=1045982"
  );
  # https://lists.fedoraproject.org/pipermail/package-announce/2015-January/147504.html
  script_set_attribute(
    attribute:"see_also",
    value:"http://www.nessus.org/u?b382b69f"
  );
  script_set_attribute(
    attribute:"solution", 
    value:"Update the affected denyhosts package."
  );
  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:fedoraproject:fedora:denyhosts");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:fedoraproject:fedora:20");

  script_set_attribute(attribute:"patch_publication_date", value:"2014/12/16");
  script_set_attribute(attribute:"plugin_publication_date", value:"2015/01/06");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_copyright(english:"This script is Copyright (C) 2015-2020 and is owned by Tenable, Inc. or an Affiliate thereof.");
  script_family(english:"Fedora Local Security Checks");

  script_dependencies("ssh_get_info.nasl");
  script_require_keys("Host/local_checks_enabled", "Host/RedHat/release", "Host/RedHat/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/RedHat/release");
if (isnull(release) || "Fedora" >!< release) audit(AUDIT_OS_NOT, "Fedora");
os_ver = eregmatch(pattern: "Fedora.*release ([0-9]+)", string:release);
if (isnull(os_ver)) audit(AUDIT_UNKNOWN_APP_VER, "Fedora");
os_ver = os_ver[1];
if (! ereg(pattern:"^20([^0-9]|$)", string:os_ver)) audit(AUDIT_OS_NOT, "Fedora 20.x", "Fedora " + os_ver);

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

cpu = get_kb_item("Host/cpu");
if (isnull(cpu)) audit(AUDIT_UNKNOWN_ARCH);
if ("x86_64" >!< cpu && cpu !~ "^i[3-6]86$") audit(AUDIT_LOCAL_CHECKS_NOT_IMPLEMENTED, "Fedora", cpu);

flag = 0;
if (rpm_check(release:"FC20", reference:"denyhosts-2.6-29.fc20.1")) 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, "denyhosts");
}

References