Vulnerabilities > CVE-2017-6638 - Improper Input Validation vulnerability in Cisco Anyconnect Secure Mobility Client

047910
CVSS 7.2 - HIGH
Attack vector
LOCAL
Attack complexity
LOW
Privileges required
NONE
Confidentiality impact
COMPLETE
Integrity impact
COMPLETE
Availability impact
COMPLETE
local
low complexity
cisco
CWE-20
nessus

Summary

A vulnerability in how DLL files are loaded with Cisco AnyConnect Secure Mobility Client for Windows could allow an authenticated, local attacker to install and run an executable file with privileges equivalent to the Microsoft Windows SYSTEM account. The vulnerability is due to incomplete input validation of path and file names of a DLL file before it is loaded. An attacker could exploit this vulnerability by creating a malicious DLL file and installing it in a specific system directory. A successful exploit could allow the attacker to execute commands on the underlying Microsoft Windows host with privileges equivalent to the SYSTEM account. The attacker would need valid user credentials to exploit this vulnerability. This vulnerability affects all Cisco AnyConnect Secure Mobility Client for Windows software versions prior to 4.4.02034. Cisco Bug IDs: CSCvc97928.

Vulnerable Configurations

Part Description Count
Application
Cisco
95

Common Weakness Enumeration (CWE)

Common Attack Pattern Enumeration and Classification (CAPEC)

  • Buffer Overflow via Environment Variables
    This attack pattern involves causing a buffer overflow through manipulation of environment variables. Once the attacker finds that they can modify an environment variable, they may try to overflow associated buffers. This attack leverages implicit trust often placed in environment variables.
  • Server Side Include (SSI) Injection
    An attacker can use Server Side Include (SSI) Injection to send code to a web application that then gets executed by the web server. Doing so enables the attacker to achieve similar results to Cross Site Scripting, viz., arbitrary code execution and information disclosure, albeit on a more limited scale, since the SSI directives are nowhere near as powerful as a full-fledged scripting language. Nonetheless, the attacker can conveniently gain access to sensitive files, such as password files, and execute shell commands.
  • Cross Zone Scripting
    An attacker is able to cause a victim to load content into their web-browser that bypasses security zone controls and gain access to increased privileges to execute scripting code or other web objects such as unsigned ActiveX controls or applets. This is a privilege elevation attack targeted at zone-based web-browser security. In a zone-based model, pages belong to one of a set of zones corresponding to the level of privilege assigned to that page. Pages in an untrusted zone would have a lesser level of access to the system and/or be restricted in the types of executable content it was allowed to invoke. In a cross-zone scripting attack, a page that should be assigned to a less privileged zone is granted the privileges of a more trusted zone. This can be accomplished by exploiting bugs in the browser, exploiting incorrect configuration in the zone controls, through a cross-site scripting attack that causes the attackers' content to be treated as coming from a more trusted page, or by leveraging some piece of system functionality that is accessible from both the trusted and less trusted zone. This attack differs from "Restful Privilege Escalation" in that the latter correlates to the inadequate securing of RESTful access methods (such as HTTP DELETE) on the server, while cross-zone scripting attacks the concept of security zones as implemented by a browser.
  • Cross Site Scripting through Log Files
    An attacker may leverage a system weakness where logs are susceptible to log injection to insert scripts into the system's logs. If these logs are later viewed by an administrator through a thin administrative interface and the log data is not properly HTML encoded before being written to the page, the attackers' scripts stored in the log will be executed in the administrative interface with potentially serious consequences. This attack pattern is really a combination of two other attack patterns: log injection and stored cross site scripting.
  • Command Line Execution through SQL Injection
    An attacker uses standard SQL injection methods to inject data into the command line for execution. This could be done directly through misuse of directives such as MSSQL_xp_cmdshell or indirectly through injection of data into the database that would be interpreted as shell commands. Sometime later, an unscrupulous backend application (or could be part of the functionality of the same application) fetches the injected data stored in the database and uses this data as command line arguments without performing proper validation. The malicious data escapes that data plane by spawning new commands to be executed on the host.

Nessus

NASL familyWindows
NASL idCISCO_ANYCONNECT_CSCVC97928.NASL
descriptionThe version of Cisco AnyConnect Secure Mobility Client installed on the remote Windows host is prior to 4.4.02034. It is, therefore, affected by a local privilege escalation vulnerability due to improper validation of paths and filenames of dynamic-link library (DLL) files before they are loaded. A local attacker can exploit this, via a specially crafted DLL file, to escalate privileges and execute commands with SYSTEM level privileges.
last seen2020-06-01
modified2020-06-02
plugin id100790
published2017-06-14
reporterThis script is Copyright (C) 2017-2019 and is owned by Tenable, Inc. or an Affiliate thereof.
sourcehttps://www.tenable.com/plugins/nessus/100790
titleCisco AnyConnect Secure Mobility Client < 4.4.02034 Local Privilege Escalation
code
#
# (C) Tenable Network Security, Inc.
#

include("compat.inc");

if (description)
{
  script_id(100790);
  script_version("1.7");
  script_cvs_date("Date: 2019/11/13");

  script_cve_id("CVE-2017-6638");
  script_bugtraq_id(98938);
  script_xref(name:"CISCO-SA", value:"cisco-sa-20170607-anyconnect");
  script_xref(name:"CISCO-BUG-ID", value:"CSCvc97928");

  script_name(english:"Cisco AnyConnect Secure Mobility Client < 4.4.02034 Local Privilege Escalation");
  script_summary(english:"Checks the version of the Cisco AnyConnect client.");

  script_set_attribute(attribute:"synopsis", value:
"A VPN application installed on the remote host is affected by a
privilege escalation vulnerability.");
  script_set_attribute(attribute:"description", value:
"The version of Cisco AnyConnect Secure Mobility Client installed on
the remote Windows host is prior to 4.4.02034. It is, therefore,
affected by a local privilege escalation vulnerability due to improper
validation of paths and filenames of dynamic-link library (DLL) files
before they are loaded. A local attacker can exploit this, via a
specially crafted DLL file, to escalate privileges and execute
commands with SYSTEM level privileges.");
  # https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170607-anyconnect
  script_set_attribute(attribute:"see_also", value:"http://www.nessus.org/u?b76d8a8e");
  script_set_attribute(attribute:"see_also", value:"https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvc97928");
  script_set_attribute(attribute:"solution", value:
"Upgrade to Cisco AnyConnect Secure Mobility Client version 4.4.02034
or later.");
  script_set_cvss_base_vector("CVSS2#AV:L/AC:L/Au:N/C:C/I:C/A:C");
  script_set_cvss_temporal_vector("CVSS2#E:U/RL:OF/RC:C");
  script_set_cvss3_base_vector("CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H");
  script_set_cvss3_temporal_vector("CVSS:3.0/E:U/RL:O/RC:C");
  script_set_attribute(attribute:"cvss_score_source", value:"CVE-2017-6638");

  script_set_attribute(attribute:"exploitability_ease", value:"No known exploits are available");
  script_set_attribute(attribute:"exploit_available", value:"false");

  script_set_attribute(attribute:"vuln_publication_date", value:"2017/06/07");
  script_set_attribute(attribute:"patch_publication_date", value:"2017/04/12");
  script_set_attribute(attribute:"plugin_publication_date", value:"2017/06/14");

  script_set_attribute(attribute:"plugin_type", value:"local");
  script_set_attribute(attribute:"cpe", value:"cpe:/a:cisco:anyconnect_secure_mobility_client");
  script_end_attributes();

  script_category(ACT_GATHER_INFO);
  script_family(english:"Windows");

  script_copyright(english:"This script is Copyright (C) 2017-2019 and is owned by Tenable, Inc. or an Affiliate thereof.");

  script_dependencies("cisco_anyconnect_vpn_installed.nasl");
  script_require_keys("installed_sw/Cisco AnyConnect Secure Mobility Client", "SMB/Registry/Enumerated");
  script_require_ports(139, 445);

  exit(0);
}

include("vcf.inc");

get_kb_item_or_exit("SMB/Registry/Enumerated");

app_info = vcf::get_app_info(app:"Cisco AnyConnect Secure Mobility Client", win_local:TRUE);

constraints = [{ "fixed_version" : "4.4.2034.0" }];

vcf::check_version_and_report(app_info:app_info, constraints:constraints, severity:SECURITY_HOLE);