Vulnerabilities > CVE-2018-3761 - Improper Authentication vulnerability in Nextcloud Server

047910
CVSS 8.1 - HIGH
Attack vector
NETWORK
Attack complexity
LOW
Privileges required
NONE
Confidentiality impact
HIGH
Integrity impact
HIGH
Availability impact
NONE
network
low complexity
nextcloud
CWE-287
nessus
NVD
Published: 2018-07-05
Updated: 2023-02-28

Summary

Nextcloud Server before 12.0.8 and 13.0.3 suffer from improper authentication on the OAuth2 token endpoint. Missing checks potentially allowed handing out new tokens in case the OAuth2 client was partly compromised.

Vulnerable Configurations

Part Description Count
Application
Nextcloud
429

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.

Nessus

  • NASL familySuSE Local Security Checks
    NASL idOPENSUSE-2018-712.NASL
    descriptionThis update for nextcloud fixes the following issues : Security issues fixed : - CVE-2018-3761: Fix improper authentication on the OAuth2 token endpoint (bsc#1100344). - CVE-2018-3762: Fix improper checks of dropped permissions for incoming shares allowing a user to still request previews for files it should not have access to (bsc#1100343).
    last seen2020-06-05
    modified2018-07-12
    plugin id111037
    published2018-07-12
    reporterThis script is Copyright (C) 2018-2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/111037
    titleopenSUSE Security Update : nextcloud (openSUSE-2018-712)
    code
    #%NASL_MIN_LEVEL 80502
#
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from openSUSE Security Update openSUSE-2018-712.
#
# The text description of this plugin is (C) SUSE LLC.
#

include("compat.inc");

if (description)
{
  script_id(111037);
  script_version("1.3");
  script_set_attribute(attribute:"plugin_modification_date", value:"2020/06/04");

  script_cve_id("CVE-2018-3761", "CVE-2018-3762");

  script_name(english:"openSUSE Security Update : nextcloud (openSUSE-2018-712)");
  script_summary(english:"Check for the openSUSE-2018-712 patch");

  script_set_attribute(
    attribute:"synopsis", 
    value:"The remote openSUSE host is missing a security update."
  );
  script_set_attribute(
    attribute:"description", 
    value:
"This update for nextcloud fixes the following issues :

Security issues fixed :

  - CVE-2018-3761: Fix improper authentication on the OAuth2
    token endpoint (bsc#1100344).

  - CVE-2018-3762: Fix improper checks of dropped
    permissions for incoming shares allowing a user to still
    request previews for files it should not have access to
    (bsc#1100343)."
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://bugzilla.opensuse.org/show_bug.cgi?id=1100343"
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://bugzilla.opensuse.org/show_bug.cgi?id=1100344"
  );
  script_set_attribute(
    attribute:"solution", 
    value:"Update the affected nextcloud package."
  );
  script_set_cvss_base_vector("CVSS2#AV:N/AC:M/Au:N/C:P/I:P/A:N");
  script_set_cvss3_base_vector("CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:novell:opensuse:nextcloud");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:novell:opensuse:15.0");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:novell:opensuse:42.3");

  script_set_attribute(attribute:"patch_publication_date", value:"2018/07/11");
  script_set_attribute(attribute:"plugin_publication_date", value:"2018/07/12");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_copyright(english:"This script is Copyright (C) 2018-2020 and is owned by Tenable, Inc. or an Affiliate thereof.");
  script_family(english:"SuSE Local Security Checks");

  script_dependencies("ssh_get_info.nasl");
  script_require_keys("Host/local_checks_enabled", "Host/SuSE/release", "Host/SuSE/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/SuSE/release");
if (isnull(release) || release =~ "^(SLED|SLES)") audit(AUDIT_OS_NOT, "openSUSE");
if (release !~ "^(SUSE15\.0|SUSE42\.3)$") audit(AUDIT_OS_RELEASE_NOT, "openSUSE", "15.0 / 42.3", release);
if (!get_kb_item("Host/SuSE/rpm-list")) audit(AUDIT_PACKAGE_LIST_MISSING);



flag = 0;

if ( rpm_check(release:"SUSE15.0", reference:"nextcloud-13.0.4-lp150.2.3.1") ) flag++;
if ( rpm_check(release:"SUSE42.3", reference:"nextcloud-13.0.4-9.1") ) 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, "nextcloud");
}
  • NASL familySuSE Local Security Checks
    NASL idOPENSUSE-2019-511.NASL
    descriptionThis update for nextcloud fixes the following issues : Security issues fixed : - CVE-2018-3761: Fix improper authentication on the OAuth2 token endpoint (bsc#1100344). - CVE-2018-3762: Fix improper checks of dropped permissions for incoming shares allowing a user to still request previews for files it should not have access to (bsc#1100343).
    last seen2020-05-31
    modified2019-03-27
    plugin id123216
    published2019-03-27
    reporterThis script is Copyright (C) 2019-2020 and is owned by Tenable, Inc. or an Affiliate thereof.
    sourcehttps://www.tenable.com/plugins/nessus/123216
    titleopenSUSE Security Update : nextcloud (openSUSE-2019-511)
    code
    #
# (C) Tenable Network Security, Inc.
#
# The descriptive text and package checks in this plugin were
# extracted from openSUSE Security Update openSUSE-2019-511.
#
# The text description of this plugin is (C) SUSE LLC.
#

include("compat.inc");

if (description)
{
  script_id(123216);
  script_version("1.3");
  script_set_attribute(attribute:"plugin_modification_date", value:"2020/05/26");

  script_cve_id("CVE-2018-3761", "CVE-2018-3762");

  script_name(english:"openSUSE Security Update : nextcloud (openSUSE-2019-511)");
  script_summary(english:"Check for the openSUSE-2019-511 patch");

  script_set_attribute(
    attribute:"synopsis",
    value:"The remote openSUSE host is missing a security update."
  );
  script_set_attribute(
    attribute:"description",
    value:
"This update for nextcloud fixes the following issues :

Security issues fixed :

  - CVE-2018-3761: Fix improper authentication on the OAuth2
    token endpoint (bsc#1100344).

  - CVE-2018-3762: Fix improper checks of dropped
    permissions for incoming shares allowing a user to still
    request previews for files it should not have access to
    (bsc#1100343)."
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://bugzilla.opensuse.org/show_bug.cgi?id=1100343"
  );
  script_set_attribute(
    attribute:"see_also",
    value:"https://bugzilla.opensuse.org/show_bug.cgi?id=1100344"
  );
  script_set_attribute(
    attribute:"solution",
    value:"Update the affected nextcloud package."
  );
  script_set_cvss_base_vector("CVSS2#AV:N/AC:M/Au:N/C:P/I:P/A:N");
  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:R/S:U/C:H/I:H/A:N");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C");
  script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"p-cpe:/a:novell:opensuse:nextcloud");
  script_set_attribute(attribute:"cpe", value:"cpe:/o:novell:opensuse:15.0");

  script_set_attribute(attribute:"vuln_publication_date", value:"2018/07/05");
  script_set_attribute(attribute:"patch_publication_date", value:"2019/03/23");
  script_set_attribute(attribute:"plugin_publication_date", value:"2019/03/27");
  script_set_attribute(attribute:"generated_plugin", value:"current");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_copyright(english:"This script is Copyright (C) 2019-2020 and is owned by Tenable, Inc. or an Affiliate thereof.");
  script_family(english:"SuSE Local Security Checks");

  script_dependencies("ssh_get_info.nasl");
  script_require_keys("Host/local_checks_enabled", "Host/SuSE/release", "Host/SuSE/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/SuSE/release");
if (isnull(release) || release =~ "^(SLED|SLES)") audit(AUDIT_OS_NOT, "openSUSE");
if (release !~ "^(SUSE15\.0)$") audit(AUDIT_OS_RELEASE_NOT, "openSUSE", "15.0", release);
if (!get_kb_item("Host/SuSE/rpm-list")) audit(AUDIT_PACKAGE_LIST_MISSING);



flag = 0;

if ( rpm_check(release:"SUSE15.0", reference:"nextcloud-13.0.4-lp150.2.3.1") ) 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, "nextcloud");
}

References